chapter iii synthesis, characterization...

CHAPTER – III

SYNTHESIS, CHARACTERIZATION AND PHOTO-LUMINESCENT

PROPERTIES OF SCHIFF BASE METAL COMPLEXES

Schiff bases have been playing an important role in the development of coordination

chemistry. Schiff base metal complexes have been studied extensively because of their wide

range of applications in various fields. These are widely applicable for their catalytic activity

in a large number of homogeneous and heterogeneous reactions.

Schiff base was reported first of all, by Hugo Schiff in 1864 [1]. Schiff bases have a

general formula with azomethine group as RHC=NR‘ where R and R‘ are alkyl, aryl, cyclo

alkyl or heterocyclic groups which may be variously substituted. These can be prepared by

condensation reaction of primary amines and carbonyl compounds in different solvents with

the elimination of water molecules and resulting in formation of imines with a characteristic

C=N double bond. The presence of dehydrating agents normally favours the formation of

Schiff bases. MgSO4 or Na2SO4 are commonly employed as a dehydrating agent. Schiff bases

are stable solids, though care should be taken in the purification steps as it undergoes

degradation. Chromatographic purification of Schiff bases on silica gel is not recommended

as they undergo hydrolysis. In such cases it is better to purify the Schiff base by

crystallization methods. The nitrogen atom of azomethine group is sp2 hybridized containing

a lone pair of electrons. These are of chemical importance and impart excellent chelating

ability when used in combination with one or more donor atoms close to the azomethine

group. The chelating ability of Schiff bases combined with an ease of preparation and

flexibility in varying chemical environment about the C=N group makes it an interesting

ligand in co-ordination chemistry [2, 3]. The Schiff base compounds of salicylaldehyde

derivative with diamine are N2O2 compounds and so called as salen ligands. This term is

originally used for salicyldehyde and ethylenediamine and now is used in the literature to

describe the class of (O, N, N, O) tetradentate bis Schiff base ligands.

Most common Schiff bases have NO or N2O2-donor atoms but the oxygen atoms can

be replaced by sulphur, nitrogen, or selenium atoms. Stereogenic centres can also be

introduced in the synthetic design of Schiff bases macrocyclic and supramolecular chemistry

[4, 5]. Schiff base ligands form stable metal complexes with most transition metal ions

prepared by treating metal salts with Schiff base ligands under suitable experimental

conditions. Cozzi [6] have reported various synthetic routes commonly employed for

preparation of Schiff base metal complexes. There are numerous literature reviews on the

synthesis and characterization of metal complexes [4, 7-9].

H

R

O H2N R'

H2OH

R

N R'

Aldehyde or ketone Primary amine Schiff base

Figure 3.1 Formations of Schiff-Bases

R R'

O

R"NH2

R

O

N

R'

H

R"

H

R"NH2

R

O

N

R'

H

R"

N

H

HH

R"

R

OH

N

R'

H

R"

N

H

HR"

H

R

O

N

R'

R"

H

HH

R"NH2

N

R

R' R"

Figure 3.2 Mechanism of Schiff base synthesis

Mechanism of condensation of carbonyl compounds with amines [5]

Organic electroluminescent devices are useful in flat panel displays since Tang and

Van Slyke reported on high performance organic electronic devices [10]. Their discovery was

based on employing a multilayer device structure containing an emitting layer and a carrier

transport layer of suitable organic materials. Organic dyes, chelate metal complexes and

polymers are the major categories of materials used in the fabrication of organic EL devices.

Transition-metal complexes have been increasingly used in the design of functional

molecular materials. In this regard, phosphorescent d6 and d

8 metal complexes containing p-

conjugated ligands with N and/or C donor atoms have been extensively studied and used in

the development of high-performance organic light emitting diodes (OLEDs) [11-13].

Materials applications of transition-metal Schiff base complexes are less developed. The

Schiff base ligands can be easily prepared and structurally modified. They have been

demonstrated to have immense practical applications, such as in the development of metal

catalysts for highly enantio-selective organic transformation reactions [14-19].

Schiff base complexes are now-a-days used as electroluminescent materials for flat

panel displays [20, 21]. Schiff base complexes with transition and non-transition metals are

used as promising materials for optoelectronic applications in flat panel displays due to their

outstanding photo and electroluminescent (PL and EL) properties, and the ease of synthesis

that readily allows structural modification for optimization of material properties [22-30].

Metal complexes offer many attractive properties, such as displaying a double role of

electron transport and light emission, higher thermal stability and their ease of sublimation.

Moreover, an attractive feature of these complexes is the ability to generate a much greater

diversity of tunable properties and their color emission by virtue of the coordinated metal

centre or by modifying the backbone substituents of ligands [20]. The introduction of

different substituent resulted in tuning of the optical properties of the Schiff base complexes

[31-34]. The highest occupied molecular orbital (HOMO) and the lowest unoccupied

molecular orbital (LUMO) are associated with the electron and hole transport properties of

the substances. The highest occupied molecular orbitals (HOMO) are mainly localized on the

oxygen atoms and lowest unoccupied molecular orbital (LUMO) are located on the nitrogen

moieties of the salicylidene moiety of salen ligands. The energy gap between HOMO‘s and

LUMO‘s changes by addition of different substituent on the ligands that is useful for color

tuning purposes.

Metal zinc complexes of Schiff base became attractive for their interesting fluorescent

properties in particular; the salicylideneamine-zinc (II) complexes exhibit photoluminescence

as well as electroluminescence [22-29]. Aluminum complexes with 8-hydroxy-quinoline and

its derivatives as Alq3 are excellent metal-chelate complexes widely used as emitting

materials and electron transporting materials in OLEDs [10, 35-37].

Salicylaldehyde schiff bases are similar to 8-hydroxyquinoline in structure in which

they have at least one hydroxyl group, a coordination nitrogen atom, and a delocalised π

conjugated system [38]. Therefore, organic metal-chelate complexes of salicylaldehyde schiff

base ligands also exhibit good luminescent properties [39–41]. Kim et. al. [40] had reported

the photoluminescence (PL) and EL of the aromatic bridged azomethine metal complexes

with beryllium, magnesium and zinc. The results indicated that some of the complexes have

complicated structures which exist as dimer or dinuclear complexes due to its rigid

conformation of the aromatic bridged structures. These complexes exhibit strong blue or

blue-green emission, but they were insoluble in common organic solvents except for

dimethylsulfoxide which has higher boiling point (b. p. 189 °C), and most of them were

difficultly sublimated in vacuum. Most of the complexes were difficultly used for fabricating

EL devices by thermal vacuum deposition or spin-coating method. To improve the properties

of solubility, stability and electron transporting capability of schiff base zinc complexes, Yu

et. al. [42, 43] reported schiff base complexes in which the ligands were condensated from

conjugated aromatic aldehydes and oxa-alkyldiamines (diglycolamine or triglycolamine).

These complexes contained hetero atoms in flexible alkyl chain, and provide coordination

atoms for metal ions, but also increase the polarity of the molecules. So the ligand backbone

may play an important role in improving stability of the complexes compared with longer

alkyl chain schiff base ligands. 2-Hydroxy-1-naphthaldehyde was used to increase the

conjugated system of the complexes which can improve their electron transport ability. Photo

physical properties of zinc (II)–Schiff base complexes containing hetero atoms in flexible

alkyl chain bridge have been reported by Yu et. al. [42, 43]. These complexes displayed

excellent blue fluorescence both in solution and in the solid state.

In the past several years, phosphorescent platinum (II) emitters were reported as

electro-phosphorescent dopant materials [44-48]. The photo-physical and electroluminescent

properties of platinum (II) Schiff base complexes were revealed which showed that they can

be useful candidates for electro-phosphorescent high-performance OLED applications [49].

The three primary color red, green and blue are used for full color displays. The blue

emitting materials are one of the color for the development of full color displays based either

on the ‗color changing medium‘ technology or the RGB filtered white emission [50-56]. The

efficiency, durability and high driven voltages for blue materials lead to poor performance of

organic electro luminescent devices (OLEDs). It was much more difficult to obtain highly

efficient blue-light emission due to its intrinsic characteristic of the large band gap of the

emitting material. This problem could be overcome by choosing selective organic

compounds, dyes or polymers such as oxadiazole [57], cyclopentadiene derivatives [58],

distylpyrazine [59], polyalkylfluorene [60], poly (p-phenylene) [61], polypyridines [62]

which emit blue light. Many blue fluorescent dyes had been explored which exhibited

excellent performance, such as distyrylarylene derivatives and the common way to improve

efficiency and stability of OLEDs was to use the fluorescent dye doping technique [59, 63,

64]. However, the doping method was rather inconvenient for device fabrication because it

was difficult to control the deposition rate in co-evaporation process and the doping ratio. In

particular organic metal complexes have attracted a lot of attentions for OLEDs applications.

However, the major disadvantages of metal-chelate complexes were the lack of suitable blue

emitting complexes.

The effect of conjugation enhancement, introduction of electron donating substituent,

and complexation on the photo-luminescent and thermal properties of tetradentate Schiff

bases of salicylaldehyde and o-vanillin derivatives and their zinc (II) complexes were well

studied by Kotova et. al [65]. Peculiarities of the synthesis of the zinc (II) complexes with

Schiff bases were considered. From density functional calculations it was confirmed that the

luminescence of these Schiff base compounds was due to the π—π* transition between

orbitals of the organic ligand and enhancement of conjugation of the chain and introduction

of electron donating substituents lead to a decrease of the energy gap and results in a

bathochromic shift of the emission maximum. Molecular geometries of salen zinc complexes

had been studied extensively [66-68]. The variability of PL and EL properties of Zn salen

complexes could originate from the molecular conformational change [69].

Mixed ligand complexes of aluminium and gallium with tridentate ligands of Schiff

bases were reported and these had better properties than Alq3. Salicylidene-o-aminophenolato

(8-quinolinato) aluminum had high efficiency as a host material for red light emitting

devices. [70]. Binuclear gallium complex with mixed ligands based on tridentate ligands of a

Schiff base and 8-hydroxyquinoline, bis(salicylidene-o-aminophenolato)-bis(8-quinolinato)-

bis-gallium (III), exhibited a combination of both intra molecular and intermolecular

interactions of the quinoline ligands, which was different from Gaq3. The binuclear complex

possessed higher luminescent efficiency and excellent thermal stability, therefore, had great

potential as an active material for OLEDs [71]. Gallium complexes with N-salicylidene-o-

aminophenol (saph2) Schiff bases, acac and alcohol acting as complex-stabilizing agents were

prepared for their use to fabricate small molecules OLED devices. Here alcohol molecules

might be lost during thermal evaporation but this did not affect functioning of the complexes

as emitting layer in the construction of SMOLEDs. The crystallographic data of the complex

showed that the geometry of the complex was planar while PL data showed a dramatic

enhancement of the emission intensity. Substitution of Methyl (EDG) or Br (EWG) saph2

shifts the EL emission to larger or smaller wavelength, respectively, and both PL and EL

intensities were enhanced by substitution [72]. Kawamoto and his co-workers reported the

synthesis of Zn (II) and Cd (II) complexes with 2-substituted benzothiazolines. Zn (II)

afforded tetrahedral mononuclear complexes, [Zn(R-Ph-C (H) =N-C6H4-S)2] with a N2S2

donor set and a distorted tetrahedral geometry. It has been found that the electronic properties

of the substituents, as well as their positions on the pendent phenyl rings of the Schiff base

ligands affect the electronic absorption spectra of the complexes. All the complexes were

luminescent in CH2Cl2/toluene glass at 77 K [73]. Recently Wang et. al reported Schiff base

zinc complexes with N-(2-hydroxybenzidene)-p-aminodimethylaniline and N-(2-hydroxy-1-

naphthidene)-p-aminodimethylaniline, these complexes exhibited good solubility in organic

solvents, excellent thermal stabilities and were suitably used for the fabrication of OLEDs.

Keeping this in view, the use of metal complexes for the fabrication of small

molecular organic light emitting devices and the suitability of Schiff base complexes for their

use in these devices as emitting layer, we have synthesized some Schiff base ligands with

salicylaldehyde and diamines. The metal complexes of these ligands with zinc and beryllium

metals were prepared and characterized. The photo-physical properties of these metal

complexes were studied and are presented in this chapter.

3.1 Synthesis of the ligands:

The ligands Schiff bases were synthesized by the standard procedure by the reaction

of salicylaldehyde with diamines under reflux in methanol [75]. The metal complexes were

synthesized using general procedure.

Schiff bases were synthesized using salicylaldehyde and amine derivatives as shown in

scheme 3.1 to 3.5.

3.1.1 Bis(salicylidene)ethylene-1, 2-diammine

[salen]

The Schiff base was synthesized by the reaction of salicylaldehyde and

ethylenediamine in 2:1 molar ratio in methanol. A solution of Salicylaldehyde (2 mmol) was

taken in 20 ml methanol then a methanolic solution of ethylene-1, 2-diamine (1 mmol) was

added dropwise with stirring to the reaction mixture. The mixture was stirred for 2 h at 60oC.

Progress of the reaction was monitored by thin layer chromatography. The yellow colored

precipitates were formed after completion of the reaction. The precipitates formed were

filtered and washed with deionised water. The product was then purified by re-crystallisation

with methanol and then dried in oven at 75oC temperature. The yield of the product was very

high ~ (87 %). The synthetic route is given below (Scheme 3.1):

CHO

OH

H2N(CH2)2NH2

Methanol, 60 oC

OH

CH=N N=HC

HO2 h

2

Scheme 3.1 Synthetic route of [salen]

3.1.2 Bis(salicylidene)propylene-1,3-diammine

[salpen]

A solution of Salicylaldehyde (2 mmol) was taken in 20 ml methanol then a

methanolic solution of propylene-1, 3-diamine (1 mmol) was added dropwise with stirring to

the reaction mixture. The mixture was stirred for 2 h at 60oC. Progress of the reaction was

monitored by thin layer chromatography. The yellow colored precipitates were formed after

completion of the reaction. The precipitates formed were filtered and washed with deionised

water. The product was then purified by re-crystallisation with methanol and then dried in

oven at 75oC temperature. The yield of the product was very high ~ (86 %). The reaction

process is given below (Scheme 3.2):

CHO

OH

H2NCH2CH2CH2NH2

Methanol, 60 oC

OH

CH=N N=HC

HO2 h2

Scheme 3.2 Synthetic route of [salpen]

3.1.3 Bis(salicylidene)butylene-1,4-diammine

[salbutene]

The Schiff base was synthesized as according to the process mentioned earlier. To a

methanolic solution of Salicyldehyde (2 mmol) and methanolic solution of butylene-1, 4-

diammine (1 mmol) was added dropwise with stirring. After 2 h of stirring at 60oC yellow

colored precipitates were formed. The precipitates formed were filtered and washed with

deionised water. The product was then purified by re-crystallisation with methanol and then

dried in oven at 75oC temperature. The yield of the product was ~ (84 %).

CHO

OH

H2N(CH2)4NH2

Methanol, 60oC

OH

CH=N N=HC

HO2 h2

(CH2)4

Scheme 3.3 Synthetic route of [salbutene]

3.1.4 Bis(salicylidene)hexylene-1, 6-diammine

[salhexene]

The Schiff base was synthesized by the reaction of salicylaldehyde and hexylene-1,6-

diamine in 2:1 molar ratio in methanol. A solution of Salicylaldehyde (2 mmol) was taken in

20 ml methanol then a methanolic solution of hexylene-1, 6-diamine (1 mmol) was added

dropwise with stirring to the reaction mixture. The mixture was stirred for 2 h at 60oC.

Progress of the reaction was monitored by thin layer chromatography. The yellow colored

precipitates were formed after completion of the reaction. The precipitates formed were

filtered and washed with deionised water. The product was then purified by re-crystallisation

with methanol and then dried in oven at 75oC temperature. The yield of the product was ~ (84

%). Scheme is shown below:

CHO

OH

H2N(CH2)6NH2

Methanol, 60 oC

OH

CH=N N=HC

HO2 h

2

(CH2)6

Scheme 3.4 Synthetic route of [salhexene]

3.1.5 Bis(salicylidene)heptylene-1,7-diammine

[salheptene]

In similar way Schiff base was synthesised by adding drop wise solution of heptylene-

1,7-diamine (1 mmol) in absolute methanol to a methanolic solution of salicylaldehyde (2

mmol) in a conical flask with magnetic stirring at 60 oC for 2 h. The product formation was

checked by thin layer chromatography. The yellow colored precipitates formed were filtered

and washed with deionised water. The compound was recrystallized with methanol and dried

in oven. The yield of the product was ~ (83 %). Scheme is shown below here (Scheme 3.5):

CHO

OH

H2N(CH2)7NH2

Methanol, 60 oC

OH

CH=N N=HC

HO2 h

2

(CH2)7

Scheme 3.5 Synthetic route of [salheptene]

3.2 Synthesis of the zinc metal complexes:

The zinc metal complexes were prepared with the above synthesized Schiff bases.

3.2.1 Bis(salicylidene)ethylene-1,2-diaminatozinc(II)

[Zn(salen)]

The metal complex was prepared by reaction of ligand bis (salicylidene) ethylene-1,

2-diamine (salen) with zinc acetate (ligand and metal) at 1:1 molar ratio in methanol. The

Schiff base ligand (1 mmol) was taken in 50 ml methanol and heated on a magnetic stirrer at

60 oC for 1 hour. The aqueous solution of zinc acetate (1 mmol) was added drop wise to the

flask with magnetic stirring. The mixture was kept at 60 oC temp for 2 hour on magnetic

stirrer. After 2 h of stirring a cream colored precipitate of the complex separated from the

reaction mixture which were filtered, washed with deionised water, ethanol and dried at 100

oC. The cream colored metal chelate gave bluish green light under UV lamp excitation

source.

OH

CH=N N=HC

HO

Zn(ac)2

O

CH=N N=HC

O

Zn60 oC, 2 h stirring

Scheme 3.6 Synthetic route of [Zn(salen)]

3.2.2 Bis(salicylidene)propylene-1,3-diaminatozinc(II)

[Zn(salpen)]

The metal complex was prepared by reaction of ligand bis (salicylidene) propylene-1,

3-diamine (salpen) with zinc acetate (ligand and metal) at 1:1 molar ratio in methanol. The

Schiff base ligand (salpen) (1 mmol) was taken in 50 ml methanol and heated on a magnetic

stirrer at 60 oC for 1 hour. The aqueous solution of zinc acetate (1 mmol) was added drop

wise to the flask with magnetic stirring. The mixture was kept at 60 oC temp for 2 h on

magnetic stirrer. After 2 h of stirring cream colored precipitate of the complex separated out

from the reaction mixture which were filtered, washed with deionised water and ethanol and

then dried at 100 oC. The cream colored metal chelate gave bluish green light under UV lamp

excitation source.

OH

CH=N N=HC

HO

Zn(ac)2

O

CH=N N=HC

O


Scheme 3.7 Synthetic route of [Zn (salpen)]

3.2.3 Bis(salicylidene)butylene-1,4-diaminatozinc(II)

[Zn(salbutene)]

The metal complex was obtained by reaction of ligand and zinc acetate in methanol as

above procedure. The Schiff base ligand (salbutene) (1 mmol) was taken in 50 ml methanol

and heated on a magnetic stirrer at 60 oC for 1 hour. The aqueous solution of zinc acetate (1

mmol) was added drop wise to the flask with magnetic stirring. The mixture was kept at 60

oC temp for 2 h on magnetic stirrer. After 2 h of stirring cream colored precipitate of the

complex separated out from the reaction mixture which were filtered, washed with deionised

water and ethanol and then dried at 100 oC. The cream colored metal chelate gave bluish light

under UV lamp excitation source.

3.2.4 Bis(salicylidene)hexylene-1,6-diaminatozinc(II)

[Zn(salhexene)]

The Schiff base ligand (salhexene) (1 mmol) was taken in 50 ml methanol and heated

on a magnetic stirrer for at 60 oC for 1 hour. The aqueous solution of zinc acetate (1 mmol)

was dropwise added to the flask with magnetic stirring. The mixture was kept at 60 oC temp

for 2 h on magnetic stirrer. After 2 h of stirring cream colored precipitate of the complex

separated out from the reaction mixture which were filtered, washed with deionised water and

ethanol and then dried at 100 oC. The cream colored metal chelate gave bluish light under UV

lamp excitation source.

OH

CH=N N=HC

HO60 oC, 2 h stirring

Zn(ac)2

O

CH=N N=HC

O

Zn

(CH2)4(CH2)4

Scheme 3.8 Synthetic route of [Zn(salbutene)]

OH

CH=N N=H

HO

Zn(ac)2

O

CH=N N=HC

O


(CH2)6 (CH2)6

Scheme 3.9 Synthetic route of [Zn(salhexene)]

3.2.5 Bis(salicylidene)heptylene-1,7-diaminatozinc(II)

[Zn (salheptene)]

The Schiff base ligand (salheptene) (1 mmol) was taken in 50 ml methanol and heated

on a magnetic stirrer at 60 oC for 1 hour. The aqueous solution of zinc acetate (1 mmol) was

dropwise added to the flask with magnetic stirring. The mixture was kept at 60 oC temp for 2

h on magnetic stirrer. After 2 h of stirring cream colored precipitate of the complex separated

out from the reaction mixture which were filtered, washed with deionised water and ethanol

and then dried at 100 oC. The cream colored metal chelate gave bluish light under UV lamp

excitation source.

OH

CH=N N=HC

HO

Zn(ac)2

O

CH=N N=HC

O


(CH2)7 (CH2)7

Scheme 3.10 Synthetic route of [Zn(salheptene)]

Characterization of ligands and metal complexes

3.3 Structural characterization

The ligands and zinc metal complexes were characterized with CHN analysis, NMR,

FTIR spectral techniques.

3.3.1 [salen]

CHN Analysis:

The C, H, N analysis of the compound indicated the formula of the compound to be

bis(salicylidene)ethylene-1,2-diamine (C16H16N2O2)

(found: C, 71.60; H, 5.98; N, 10.47; calc.: C, 71.64; H, 5.97; N, 10.45%)

FTIR Analysis:

The broad characteristics peak at 3050 cm-1

represented the O-H stretching vibration.

This peak was at the lower side due to internal hydrogen bonding. The peak centred at 2955

cm-1

was attributed to the stretching vibration of C-H bond in the aromatic ring. The peak at

1678 cm-1

represented the C=N vibrational absorption. The peaks at 1219 cm-1

represented the

C-O stretching vibrations. The characteristics peaks from 600 to 800 cm-1

showed the

presence of benzene rings.

1HNMR:

The 1HNMR spectral studies of bis(salicylidene)ethylene-1,2-diamine taken in CDCl3

showed the peaks for hydrogens were present at 13.20 (s 2H) for hydroxyl protons; 8.33 (s 2

H) for azomethine protons and 7.29-6.80 (m 8H), 3.90 (s 4H).

3.3.2 [salpen]

CHN Analysis:


bis (salicylidene)propylene-1,3-diamine (C17H18N2O2)


FTIR Analysis:


represented the O-H stretching vibration

and showed that there was internal hydrogen bonding. The peak cantered at 2944 cm-1

was

assigned to the stretching vibration of C-H bond in the aromatic ring. The peak at 1656 cm-1

showed the C=N vibrational absorption. The peaks at 1209 cm-1

represented the C-O

stretching vibrations and the characteristics peaks of benzene rings from 600 to 800 cm-1

showed the presence of benzene rings.

1HNMR

The 1HNMR spectral studies of bis(salicylidene)propylene-1,3-diamine taken CDCl3

showed the peaks for hydrogens were present at 13.51 (s 2H) for hydroxyl protons; 8.34 (s

2H) for azomethine protons and 7.31-6.80 (m 8H), 3.69 (m 4H), 2.13 (m 2H).

3.3.3 [salbutene]

CHN Analysis:


bis (salicylidene)butylene-1,4-diamine (C18H20N2O2)


FTIR Analysis:


represented the O-H stretching vibration,

it was internally hydrogen bonded. The peak centred at 2944 cm-1

was attributed to the

stretching vibration of C-H bond in the aromatic ring. The peak at 1672 cm-1

represented the

C=N vibrational absorption. The peaks at 1210 cm-1

represented the C-O stretching

vibrations. The characteristics peaks of benzene rings were present from 600 to 800 cm-1

.

1HNMR

The 1HNMR spectral studies of bis(salicylidene)butylene-1,4-diamine taken in CDCl3


2H) for azomethine protons and 7.33-6.80 (m 8H), 3.71 (m 4H), 2.14 (m 4H).

3.3.4 [salhexene]

CHN Analysis


bis (salicylidene)hexylene-1,6-diamine (C20H24N2O2)


FTIR Analysis


represented the O-H stretching vibration,

this was internally hydrogen bonded. The peak centred at 2964 cm-1



represented the

C=N stretching vibration. The peaks at 1214 cm-1

represented the C-O stretching vibrations.

The characteristics peaks of benzene rings from 600 to 800 cm-1

showed the presence of

benzene rings.

1HNMR

The 1HNMR spectral studies of bis(salicylidene)hexylene-1,6-diamine taken in CDCl3


2H) for azomethine protons and 7.31-6.80 (m 8H), 3.60 (s 4H), 2.55 (m 4H), 1.70 (m 2H),

1.44(m 2H).

3.3.5 [salheptene]

CHN Analysis


bis (salicylidene) heptylene-1, 7-diamine (C21H26N2O2)


FTIR Analysis:


represented the O-H stretching vibration

was hydrogen bonded. The peak centered at 2984 cm-1

was attributed to the stretching

vibration of C-H bond in the aromatic ring. The peak at 1646 cm-1

represented the C=N

vibrational absorption. The peaks at 1212 cm-1

represented the C-O stretching vibrations. The

characteristics peaks from 600 to 800 cm-1


1HNMR

The 1HNMR spectral studies of bis(salicylidene)heptylene-1,7-diamine taken in

CDCl3 showed the peaks for hydrogens were present at 13.60 (s 2H) for hydroxyl protons;

8.45 (s 2H) for azomethine protons and 7.32-6.80 (m 8H), 3.63 (s 4H), 2.58 (m 4H), 1.73 (m

2H), 1.48(m 2H), 1.38 (m 2H).

3.3.6 [Zn(salen)]

CHN Analysis

The C, H, N analysis of the complex indicated the formula of the complex to be Bis

(salicylidene)ethylene-1,2-diaminato zinc (II) (C16H14N2O2Zn)

(found: C, 57.89, H, 4.25, N, 8.47, cal: C, 57.93, H, 4.22, N, 8.44% )

1HNMR

The 1HNMR spectral studies of the complex taken in DMSOD6 showed that the peaks

for aromatic hydrogens were present at 3.91 (m 4H), 6.94-7.30 (m 8H), 8.34 (s 2H). The

singlet peak due to hydroxyl proton at 13.2 (s 2H) {which was present in bis(salicylidene)

ethylene-1,2-diamine} were absent in the 1HNMR spectra of the complex and confirmed the

formation of the complex. The results showed that the peaks shifted significantly downfield

against the 1HNMR peak values of the ligand itself, indicated the formation of the reported

complex.

FTIR Analysis:


was absent in the spectra which confirmed

the formation of the complex. The peak centered at 2904 cm-1

was attributed to the stretching

vibration of C-H bond in the aromatic ring. The peak at 1620 cm-1

represented the C=N

vibrational absorption. There was shift in the stretching frequency due to donation of electron

density as compared to ligand. The peaks at 1197 cm-1


vibrations, it also shifted to low value as compared to ligand. The characteristics peaks of

benzene rings from 600 to 800 cm-1

showed the presence of benzene rings. This confirmed

the formation of the zinc complex.

3.3.7 [Zn(salpen)]

CHN Analysis:

The C, H, N analysis of the complex indicated the formula of the complex to be Zn

(salpen) (C17H16N2O2Zn)

(found: C, 59.01; H, 4.65; N,8.12; calc.: C, 59.06; H, 4.63; N, 8.106%)

1HNMR


for aromatic hydrogens were present at 2.56 (m 2H), 3.68 (m 2H), 3.83 (m 2H), 6.83-7.25 (m

8H), 8.32 (s 2H). The singlet peak due to hydroxyl proton at 13.15 (s 2H) {which was present

in bis(salicylidene)propylene-1,3-diamine} were absent in the 1HNMR spectra of the

complex and confirmed the formation of the complex. The results showed that the peaks

shifted significantly downfield against the 1HNMR peak values of the ligand itself, indicated

the formation of the reported complex.

FTIR Analysis:


were absent in the spectra which

confirmed the formation of the complex. The peak centred at 2904 cm-1



represented the

C=N vibrational absorption. There was shift in the stretching frequency due to donation of

electron density as compared to ligand. The peak at 1195 cm-1


vibrations also shift to low value. The characteristics peaks from 600 to 800 cm-1

showed the

presence of benzene rings.

3.3.8 [Zn(salbutene)]

CHN Analysis


(salbutene) (C18H18N2O2Zn)

(found: C, 60.06, H, 5.02, N, 7.75, cal: C, 60.10, H, 5.0, N, 7.79% )

1HNMR

The 1HNMR spectral studies of the Bis(salicylidene)butylene-1,4-diaminatozinc(II)

taken in DMSOD6 showed that the peaks for aromatic hydrogens were present at 2.15 (m

4H), 3.72 (m 4H), 6.89-7.30 (m 8H), 8.35 (s 2H). The singlet peak due to hydroxyl proton at

13.43 (s 2H) {which was present in Bis(salicylidene)butylene-1,4-diamine} were absent in

the 1HNMR spectra of the complex and confirmed the formation of the complex. The results

showed that the peaks shifted significantly downfield against the 1HNMR peaks values of the

ligand itself, taken from literature indicated the formation of the reported complex.

FTIR Analysis






represented the

C=N vibrational absorption. There was shift in the stretching frequency due to donation of

electron density as compared to ligand. The peaks at 1186 cm-1

represented the C-O

stretching vibrations also shift to lower value. The characteristics peaks from 600 to 800 cm-1


3.3.9 [Zn(salhexene)]

CHN Analysis


(salhexene) (C20H22N2O2Zn)

(found: C, 61.92, H, 5.69, N, 7.25, cal: C, 61.95, H, 5.67, N, 7.22% )

1HNMR


for aromatic hydrogens were present at 1.45 (m 2H), 1.71 (m 2H), 2.56 (m 4H), 3.60 (m 4H),

6.87-7.30 (m 8H), 8.41 (s 2H). The singlet peak due to hydroxyl proton at 13.54 (s 2H)

{which was present in bis(salicylidene)hexylene-1,6-diamine} were absent in the 1HNMR

spectra of the complex and confirmed the formation of the complex. The results showed that

the peaks shifted significantly downfield against the 1HNMR peak values of the ligand itself,

indicated the formation of the reported complex

FTIR Analysis






represented the

C=N stretching vibration. There was shift in the stretching frequency due to donation of


represented the C-O

stretching vibrations also shifted to low value. The characteristics peaks from 600 to 800 cm-1


3.3.10 [Zn(salheptene)]

CHN Analysis


(salheptene) (C21H24N2O2Zn)

(found: C, 62.74, H, 5.99, N, 7.00, cal: C, 62.78, H, 5.97, N, 6.97% )

1HNMR



3.68 (m 4H), 6.83-7.30 (m 8H), 8.45 (s 2H). The singlet peak due to hydroxyl proton at 13.60

(s 2H) {which was present in bis(salicylidene)heptylene-1,7-diamine} were absent in the

1HNMR spectra of the complex and confirmed the formation of the complex. The results

showed that the peaks shifted significantly downfield against the 1HNMR peak values of the

ligand itself, indicated the formation of the reported complex.

FTIR Analysis






represents the



represented the C-O

stretching vibrations also shift to lower value. The characteristics peaks from 600 to 800 cm-1


3.4 Solubility

All the zinc Schiff bases were insoluble in common organic solvents. They are

sparingly soluble in methanol. However the complexes showed good solubility in DMSO

solvent.

3.5 Thermal characterization (TGA)

Thermo-gravimetric analysis (TGA) of the samples was carried out to investigate the

thermal stability of the metal organic framework. The TGA of zinc metal complexes was

done over a temperature range from 25-600 oC at a scan rate of 10

oC/min in nitrogen

atmosphere.

3.5.1 [Zn(salen)]

Curve of fig. 3.3 corresponds to TGA of Zn(salen) in nitrogen atmosphere. It can be

seen from the TGA data that complex exhibited good thermal stability. The onset temperature

of weight loss was 320 oC and 10% weight loss occurred at 350

oC. At 380

oC the complex

weight loss occurred and decomposed completely.

3.5.2 [Zn(salpen)]

Curve of fig. 3.4 corresponds to TGA of Zn(saplen) in nitrogen atmosphere. It can be



oC. At 460

oC the complex



Curve of fig. 3.5 corresponds to TGA of Zn(sabutene) in nitrogen atmosphere. It can

be seen from the TGA data that complex exhibited good thermal stability. The onset

temperature of weight loss was 230 oC and 10% weight loss occurred at 350

oC. At 370

oC

the complex weight loss occurred and decomposed completely.

Figure: 3.3 TGA graph of Zn(salen)

Figure: 3.4 TGA graph of Zn(salpen)

Figure: 3.5 TGA graph of Zn(salbutene)


100 200 300 400 500 600 700 800 900 100040

50

60

70

80

90

100

Per

cen

tag

e W

t lo

ss

Temperature (oC)

TGA Curve

100 200 300 400 500 600 700 800 900 100040

50

60

70

80

90

100

Per

cen

tag

e W

t lo

ss

Temperature (oC)

TGA Curve

100 200 300 400 500 60070

75

80

85

90

95

100

Per

cen

tag

e W

t lo

ss

Temperature (oC)

TGA Curve

Curve of fig. 3.6 corresponds to TGA of Zn(salhexene) in nitrogen atmosphere. It can



oC. At 380

oC the

complex weight loss occurred and decomposed completely.


Curve of fig. 3.7 corresponds to TGA of Zn(salheptene) in nitrogen atmosphere. It can



oC. At 390

oC


Figure: 3.6 TGA graph of Zn(salhexene)

Figure: 3.7 TGA graph of Zn(salheptene)

3.6 UV-Visible absorption and photoluminescence (PL) characterization

100 200 300 400 500 60065

70

75

80

85

90

95

100

Per

cen

tag

e W

t lo

ss

Temperature (oC)

TGA Curve

100 200 300 400 500 600

50

60

70

80

90

100

Per

cen

tag

e W

t lo

ss

Temperature (oC)

TGA Curve

The UV-visible absorption bands of the zinc complexes match closely with the

protonated ligand precursor. The electronic spectra of zinc complexes show metal perturbed

ligand centered transitions. The metal complexes show absorption peaks due to n → π٭ and π

→ π٭ electronic transitions. The band gap energy was measured from the absorption

spectrum. Upon excitation at absorption wavelengths these materials fluoresced in the visible

region of the spectra. The complexes showed good luminescence in solid state as well as

solution state. As there are no d-d transitions in zinc complexes and the emission of light is

assigned as relaxation from higher energy level to the lower energy level due to ligand

centered transitions.

3.6.1 [Zn(salen)]

Excitation and emission spectra were recorded on Horiba Jobin YVON Fluolog

Model No FL 3-11 spectro fluorometer. The excitation and emission spectra of the complex

were taken in methanol solvent. Fig. 3.8 shows the excitation and emission spectra of the

complex. Curve (a) and Curve (b) are the excitation and emission spectra of the complex

respectively. Two absorption peaks one at 271 nm and another at 360 nm were observed. It

implies clearly that low energy peak belongs to the n → π٭ transitions localized on the

aromatic ring of the ligand and a high energy peak at 271 nm belongs to the ligand centred π

→ π٭ transitions.

Figure 3.8 UV-vis absorption and photo-luminescent emission of [Zn(salen)]

300 400 500 600 700 800

0.0

0.4

0.8

1.2

1.6

2.0

2.4

2.8

Inte

nsi

ty(a

.u.)

Wavelength(nm)

UV-vis

Figure 3.9 Square of absorption vs energy curve of [Zn(salen)]

The optical band gap of the complex was calculated by plotting graph between

absorbance2 Vs energy [76] as shown in fig. 3.9, it was found 3.03 (eV). Complex exhibited

strong fluorescence at 447 nm in the spectrum upon excitation at 271 nm and 360 nm

wavelengths. In emission spectrum, broad peak at 447 nm resulting in a bright blue emission

had a considerable intensity as shown in curve B of fig. 3.8. The emitted color of

photoluminescence was blue having CIE (1931) color coordinates at x = 0.15, y = 0.11.

3.6.2 [Zn (salpen)]

The excitation and emission spectra of the complex were taken in methanol solvent.

Fig. 3.10 shows the excitation and emission spectra of the complex. Curve (a) and Curve (b)

are the excitation and emission spectra of the complex respectively. Two absorption peaks

one at 263 nm and another at 349 nm were observed. It implies clearly that low energy peak

at 349 nm belongs to the n → π٭ transitions localized on the aromatic ring of the ligand and a

high energy peak at 263 nm belongs to the ligand centred π → π٭ transitions. The optical

band gap of the complex was calculated by plotting graph between absorbance2 Vs energy, it

was found 3.14 (eV) as shown in fig. 3.11. Complex exhibited strong fluorescence at 440 nm

in the spectrum upon excitation at 267 nm and 354 nm wavelengths. In emission spectrum,

broad peak at 440 nm resulting in a bright blue emission had a considerable intensity as

shown in fig. 3.10. The emitted color of photoluminescence was blue having CIE (1931)

color coordinates at x = 0.15, y = 0.11.

1.5 2.0 2.5 3.0 3.5 4.0 4.5

0.0

0.2

0.4

0.6

0.8

1.0

Optical band gapA

bso

rba

nce

2

Energy(eV)

[Zn(salen)]

Figure 3.10 UV-vis and photo-luminescent [Zn(salpen)]

Figure 3.11 Square of absorption vs energy curve of [Zn(salpen)]






at 354 belongs to the n → π٭ transitions localized on the aromatic ring of the ligand and a


band gap of the complex was calculated by plotting graph between absorbance2 Vs energy

shown in fig. 3.13, it was found 3.15 (eV).

300 400 500 600 700 800

0.0

0.2

0.4

0.6

0.8

1.0

No

rm

ali

zed

In

ten

sity

(a.u

.)

Wavelength(nm)

UV-Vis

1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

0.00

0.05

0.10

0.15

0.20

0.25

0.30

Optical band gap

Ab

sorb

an

ce2

Energy(eV)

[Zn(salpen)]

Figure 3.12 UV-visible and PL of [Zn(salbutene)]

Complex exhibited strong fluorescence at 436 nm in the spectrum upon excitation at

267 nm and 354 nm wavelengths. In emission spectrum, broad peak at 436 nm resulting in a

bright blue emission had a considerable intensity as shown in fig. 3.12. The emitted color of

photoluminescence was blue having CIE (1931) color coordinates at x = 0.15, y = 0.07.

Figure 3.13 Square of absorption vs energy curve of [Zn(salbutene)]


The excitation and emission spectra of the complex were taken in methanol solvent. Fig. 3.14

shows the excitation and emission spectra of the complex. Curve (a) and Curve (b) are the

excitation and emission spectra of the complex respectively. Two absorption peaks one at 261

nm and another at 347 nm were observed. It implies clearly that low energy peak at 347 nm

300 400 500 600 700 8000.0

0.2

0.4

0.6

0.8

1.0N

orm

ali

zed

In

ten

sity

(a.u

.)

Wavelength(nm)

UV-vis

1.5 2.0 2.5 3.0 3.5 4.0 4.5

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Optical band gap

Ab

sorb

an

ce2

Energy(eV)

[Zn(salbutene)]

belongs to the n → π٭ transitions localized on the aromatic ring of the ligand and a high

energy peak at 261 nm belongs to the ligand centred π → π٭ transitions. The optical band

gap of the complex was calculated by plotting graph between absorbance2 Vs energy shown

in fig. 3.15, it was found 3.74 (eV). Complex exhibited strong fluorescence at 433 nm in the

spectrum upon excitation at 261 nm and 347 nm wavelengths. In emission spectrum, broad

peak at 433 nm resulting in a bright blue emission had a considerable intensity as shown in

fig. 3.14. The emitted color of photoluminescence was blue having CIE (1931) color

coordinates at x = 0.15, y = 0.09.

Figure 3.14 UV-vis absorption and PL emission spectra of [Zn(salhexene)]

Figure 3.15 Square of absorption vs energy curve of [Zn(salhexene)]

250 300 350 400 450 500 550 600 650 700

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

No

rm

ali

zed

In

ten

sity

(a.u

.)

Wavelength(nm)

UV-Vis

1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

Optical band gap

Ab

sorb

an

ce2

Energy(eV)

[Zn(salhexene)]







high energy peak at 268 nm belongs to the ligand centred π → π٭ transitions.

Figure 3.16 UV-vis and PL of [Zn (salheptene)]


absorbance2 Vs energy, it was found 3.98 (eV) shown in fig. 3.17. Complex exhibited strong

fluorescence at 430 nm in the spectrum upon excitation at 261 nm and 347 nm wavelengths.

In emission spectrum, broad peak at 430 nm resulting in a bright blue emission had a

considerable intensity as shown in fig. 3.16. The emitted color of photoluminescence was

blue having CIE (1931) color coordinates at x = 0.15, y = 0.13.

300 400 500 600 700 800

0.1

0.2

0.3

0.4

0.5

0.6

No

rma

lize

d I

nte

nsi

ty(a

.u.)

Wavelength(nm)

UV-Vis

Figure 3.17 Square of absorption vs energy curve of [Zn(salheptene)]

Table: 3.1 Photo-physical properties of zinc metal complexes

Compound UV-vis absorption, λmax(nm) PL

λmax(nm)

CIE

X/Y

Color of

Emitted Light π- π*, n- π

*,

[Zn(salen)] 271 360 447 x=0.15, y=0.11 Blue

[Zn(salpen)] 263 349 440 x=0.15, y=0.11 Blue

[Zn(salbutene)] 267 354 436 x=0.15, y=0.07 Blue

[Zn(salhexene)] 261 347 433 x=0.15, y=0.09 Blue

[Zn(salheptene)] 265 353 430 x=0.15, y=0.13 Blue

Figure 3.18 Combined UV-visible spectra Schiff base zinc complexes

1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Optical band gap

Ab

sorb

an

ce2

Energy(eV)

[Zn(salheptene)]

300 400 500 600 700 800

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

No

rma

lize

d I

nte

nsi

ty(a

.u.)

Wavelength(nm)

[Zn(salen)]

[Zn(salpen)]

[Zn(salbutene)]

[Zn(salhexene)]

[Zn(salheptene)]

Figure 3.19 Combined photo-luminescent spectra of zinc Schiff base complexes

3.6.6 Discussion-

Schiff bases are known for their complex formation with various metal ions and for

their applications as emissive materials in organic light emitting diodes. In the present work

schiff base complexes of salicylaldehyde and diamines had synthesized and their

photophysical properties were studied. A series of Schiff base ligands of salicylaldehyde and

different diamines had synthesized, zinc complexes had been prepared with these ligands.

This was done to tune the color for the fabrication of full color displays for use of these metal

complexes as emissive layer in OLEDs. These complexes emit blue light under UV-visible

radiations absorption. [Zn(salen)] complex emit at 447 nm, [Zn(salpen)] emit at 440 nm,

[Zn(salbutene)] emit at 436 nm, [Zn(salhexene)] emit at 433, [Zn(salheptene)] emit at 430

nm. All these metal complexes had high thermal stability. On increasing the number of alkyl

groups in bridging chain in Schiff base ligands, there was blue shift in emission wavelengths

of complexes, this might be due to slight decrease in conjugation chain.

Synthesis and Characterization of Beryllium complexes

3.7 Synthesis

The beryllium metal complexes were synthesized with above synthesized Schiff

bases.

3.7.1 Bis(salicylidene)ethylene-1,2-diaminatoberyllium(II)

[Be(salen)]

350 400 450 500 550 600 650

0.0

0.2

0.4

0.6

0.8

1.0

No

rma

lize

d I

nte

nsi

ty(a

.u.)

Wavelength(nm)

[Zn(salen)]

[Zn(salpen)]

[Zn(salbutene)]

[Zn(salhexene)]

[Zn(salheptene)]

The metal complex was prepared by reaction of ligand Bis (salicylidene) ethylene-1,

2-diamine (salen) with beryllium sulphate (ligand and metal) at 1:1 molar ratio in methanol.

The ligand (salbutene) was prepared by adding dropwise solution of ethylene-1, 2-diamine

(1mM) in absolute methanol to a methanolic solution of salicylaldehyde (2mM) with

magnetic stirring at 60 oC for 2 h. The beryllium metal complex was then prepared by drop

wise addition of aqueous beryllium sulphate (1mM) to the above solution with stirring at 60

oC. After 2 h of stirring a cream colored precipitate of the complex was separated from the

reaction mixture which was filtered and dried at 100 oC.

3.7.2 Bis(salicylidene)butylene-1,4-diaminatoberyllium(II)

[Be(salbutene)]

The metal complex was obtained by reaction of ligand Bis (salicylidene) butylene-1,

4-diamine (salbutene) with beryllium sulphate (ligand and metal) at 1:1 molar ratio in

methanol. The ligand (salbutene) was prepared by adding drop wise solution of butylene-1, 4-

diamine (1mM) in absolute methanol to a methanolic solution of salicylaldehyde (2mM) with

magnetic stirring at 60 oC for 2 h. The beryllium metal complex was then prepared by drop

wise addition of aqueous beryllium sulphate (1mM) to the above solution with stirring at 60

oC. After 2 h of stirring a cream colored precipitate of the complex was separated from the

reaction mixture which was filtered and dried at 100 oC.

OH

CH=N N=HC

HO60 oC, 2 h stirring

BeSO4

O

CH=N N=HC

OBe

Scheme 3.11 Synthetic route of [Be(salen)]

OH

CH=N N=HC

HO600C,2 hrs stirring

BeSO4

O

CH=N N=HC

O

Be

(CH2)4 (CH2)4

Scheme 3.12 Synthetic route of [Be(salbutene)]

3.8 Structural Characterization

3.8.1 [Be(salen)]

CHN Analysis

The C, H, N analysis of the complex indicated the formula of the complex to be Be

(salen) (C16H14N2O2Be)

(found: C, 69.75, H, 5.12, N, 10.20, cal: C, 69.81, H, 5.09, N, 10.18% )

FTIR Analysis






represented the



represented the C-O

stretching vibrations. The characteristics peaks from 600 to 800 cm-1


benzene rings.

1HNMR

The 1HNMR spectral studies of the complex taken in CDCl3 showed that the peaks for

aromatic hydrogens were present at 3.92 (m 4H), 6.93-7.30 (m 8H), 8.33 (s 2H). The singlet

peak due to hydroxyl proton at 13.2 (s 2H) {which was present in bis(salicylidene) ethylene-

1, 2-diamine} were absent in the 1HNMR spectra of the complex and confirmed the

formation of the complex. The results showed that the peaks shifted significantly downfield

against the 1HNMR peak values of the ligand itself, indicated the formation of the reported

complex

3.8.2 [Be(salbutene)]

CHN Analysis

The C, H, N analysis of the complex indicated the formula of the complex to be Be

(salbutene) (C18H18N2O2Be)

(found: C, 71.18, H, 5.96, N, 9.28, cal: C, 71.287, H, 5.94, N, 9.24% )

1HNMR

The 1HNMR spectral studies of the Be(salbutene) taken in CDCl3 showed that the peaks


6.64-7.35 (m 8H), 8.22 (s 2H). The singlet peak due to hydroxyl proton at 13.2(s 2H) {which

was present in Bis(salicylidene)butylene-1,4-diamine} were absent in the 1HNMR spectra of

the complex and confirmed the formation of the complex. The results showed that the peaks

shifted significantly downfield against the 1HNMR peaks values of the ligand itself, taken

from literature indicated the formation of the reported complex.

FTIR Analysis






represented the



represented the C-O

stretching vibrations. The characteristics peaks from 600 to 800 cm-1


benzene rings.

3.9 Thermal characterization (TGA)

Thermo-gravimetric analysis (TGA) of the samples was carried out to investigate the

thermal stability of the metal organic framework. The TGA of beryllium metal complexes

was done over a temperature range from 25-600 oC at a scan rate of 10

oC/min in nitrogen

atmosphere.

3.9.1 [Be(salen)]

Curve of fig.3.20 corresponds to TGA of Be(salen) in nitrogen atmosphere. It can be



oC. At 330

oC the complex



Curve of fig.3.21 corresponds to TGA of Be(salbutene) in nitrogen atmosphere. It can



oC. At 330

oC


Figure: 3.20 TGA graph of Be(salen)

Figure: 3.21 TGA graph of Be(salbutene)

3.10 UV-visible and photo-luminescent characterization

3.10.1 [Be(salen)]


Figure 3.22 shows the excitation and emission spectra of the complex. Curve (a) and Curve

(b) are the excitation and emission spectra of the complex respectively. Two absorption peaks



high energy peak at 268 nm belongs to the ligand centred π → π٭ transitions.

100 200 300 400 500 60030

40

50

60

70

80

90

100

Per

cen

tag

e W

t lo

ss

Temperature (oC)

TGA Curve

100 200 300 400 500 600

40

50

60

70

80

90

100

Per

cen

tag

e W

t lo

ss

Temperature (oC)

TGA Curve

Figure 3.22 UV-visible and PL of [Be(salen)]


absorbance2 Vs energy shown in fig. 3.23, it was found 3.12 (eV). Complex exhibited strong

fluorescence at 425 nm in the spectrum upon excitation at 268 nm and 347 nm wavelengths.

In emission spectrum, broad peak at 425 nm resulting in a bright blue emission had a

considerable intensity as shown in fig. 3.22. The emitted color of photoluminescence was

blue having CIE (1931) color coordinates at x = 0.30, y = 0.15.

Figure 3.23 Square of absorption vs energy curve of [Be(salen)]



Figure 3.24 shows the excitation and emission spectra of the complex. Curve (a) and Curve

300 400 500 600 700 8000.00

0.05

0.10

0.15

0.20

0.25N

orm

ali

zed

In

ten

sity

(a.u

)

Wavelength(nm)

UV-vis

1.5 2.0 2.5 3.0 3.5 4.0 4.5

0.0

0.1

0.2

0.3

0.4

0.5

Optical band gap

Ab

sorp

tio

n2

Energy(eV)

[Be(salen)]

(b) are the excitation and emission spectra of the complex respectively. Two absorption peaks


at 353 belongs to the n → π٭ transitions localized on the aromatic ring of the ligand and a


band gap of the complex was calculated by plotting graph between absorbance2 Vs energy

shown in fig. 3.25, it was found 3.14 (eV). Complex exhibited strong fluorescence at 425 nm

in the spectrum upon excitation at 268 nm and 353 nm wavelengths. In emission spectrum,

broad peak at 425 nm resulting in a bright blue emission had a considerable intensity as

shown in fig. 3.24. The emitted color of photoluminescence was blue having CIE (1931)

color coordinates at x = 0.16, y = 0.058.

Figure 3.24 UV-vis absorption and PL of [Be(salbutene)]

Figure 3.25 Square of absorption vs energy curve of [Be(salbutene)]

300 400 500 600 700 8000.0

0.2

0.4

0.6

0.8

1.0

No

rma

lize

d I

nte

nsi

ty(a

.u.)

Wavelength(nm)

UV-Vis

1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

0.0

0.2

0.4

0.6

0.8

1.0

Optical band gap

Ab

sorb

an

ce2

Energy(eV)

[Be(salpen)]

Table: 3.2 Photo-physical properties of beryllium metal complexes

Compound UV-vis absorption, λmax(nm) PL

λmax(nm)

CIE

X/Y

Color of

Emitted Light π- π*, n- π

*,

[Be(salen)] 268 347 425 x=0.30, y=0.15 Blue

[Be(salbutene)] 268 353 425 x=0.16, y=0.06 Blue

Figure 3.26 Combined UV-visible spectra of Schiff base beryllium complexes

Figure 3.27 Combined photo-luminescent spectra of Schiff base beryllium complexes

300 400 500 600 700 8000.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

No

rma

lize

d I

nte

nsi

ty(a

.u.)

Wavelength(nm)

[Be(salen)]

[Be(salbutene)]

350 400 450 500 550 600 6500.0

0.2

0.4

0.6

0.8

1.0

No

rma

lize

d I

nte

nsi

ty(a

.u.)

Wavelength(nm)

[Be(salen)]

[Be(salbutene)]

3.11.3 Discussion-

The blue emitting materials are one of the colors for the development of full color

displays based either on the ‗color changing medium‘ technology or the RGB filtered white

emission. Salicylaldehyde Schiff base ligands are similar in structure with 8-

hydroxyquinoline ligand in having at least one hydroxyl group, a coordination nitrogen atom,

and a delocalised π-conjugated system. Keeping this in view, beryllium complexes with

Schiff base ligands had synthesized. These emit blue light under UV excitation with high

intensity. [Be(salen)] emit at 425 nm, [Be(salbutene)] emit at 425 nm, the emission spectrum

of [Be(salen)] was in broad range than [Be(salbutene)] PL spectrum. Beryllium complexes

emit at lower wavelength as compared to the zinc complexes this may be due to increase in

covalent bonding with increase in size as compared to ionic nature. These complexes could

be used as blue light emitting materials for optoelectronic applications.

3.12 Conclusion-

In conclusion some N, O donating azomethine ligands with salicylaldehyde and

different diamines had synthesized. Zinc and beryllium complexes were synthesized with

these ligands. These complexes could be suitable emission source for fabrication of organic

light emitting devices. These complexes showed high luminescence intensity under UV

excitation. The color was tuned by using different bridging ligand as different derivatives of

diamines. With increase in methyl group in bridging group there occurs blue shift in emission

wavelength. The synthesized metal chelates showed excellent luminescent properties emitting

blue light as reported here. Beryllium complexes emit at lower wavelength than zinc Schiff

base complexes. The blue light emitting zinc complexes are less reported, synthesized zinc

complexes can be used as blue light emitting materials for display applications.

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chapter iii synthesis, characterization...

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