Fluorescent Dyes in Organometallic Chemistry: Coumarin-tagged

NHC-Metal Complexes

Oliver Halter and Herbert Plenio

Organometallic Chemistry, Technische Universität Darmstadt, Alarich-Weiss-Str. 12,

64287 Darmstadt, Germany

e-mail: plenio@tu-darmstadt.de

Concept

Conclusions

Results

Synthesis

Solution of

Complex

Monitoring of changes in the fluorescence emission

Fluorescence intensity vs. time plotfor the reactions of [IrCl(cod)(9)]

(black) and [RhCl(cod)(9)] (red)(c= 2·10-6 mol·L-1 C2H4Cl2, 25 oC) with

an excess of CO gas (excess)

Fluorescence traces for the reaction of[IrCl(cod)(9)] (c= 2·10-6 mol·L-1 C2H4Cl2,

25 oC) with an excess of CO gas (excess)

Monitoring of the Reaction of [MCl(cod)(9)] (M=Ir, Rh) Complexes with CO

+L2

-L1

• Monitoring of ligand exchange reactions on the metal center;

• Design of fluorescent sensor and chemodosimeter

• Advantage: coumarin is an UV-excitable fluorophore

• Coumarin is easily available

Manipulation of electron density at

metals center lead to changes in

the brightness of the coumarin

We have synthesized coumarin-tagged NHC-metal complexes.

Complexes are characterized by very different fluorescence properties: strongly quenched complexes ( < 1%) with Ru or electron-rich Ir and Rh,a partially quenched Pd complex and a strongly fluorescent Au complex.

The manipulation of the electron density at the transition metals appears to modulate the efficiency of PET quenching, since electron-richtransition metals lead to decreased fluorescence, while electron-deficient metal centers lead to enhanced fluorescence emission.

Improved CO-sensitive molecular probes have been developed, which are characterized by a very good turn-on ratio and UV-excitablefluorophore.

O. Halter and H. Plenio, Eur. J. Inorg. Chem. 2018, 2935–294

• [(9)RhCl(CO)2] is more than 20 times brighter than [(9)RhCl(cod)]

• Less than 3 s it takes for the conversion of [(9)Rh(cod)] to [(9)Rh(CO)2] and 30 s

for Ir complex

• The addition of thiol and hünig base to [AuCl(9)] leads to formation of well-

known gold thiolato complex with almost quenched fluorescence because of

significantly increased electron density at the gold.

• The substitution reaction of cod with two molecules of CO converts weakly

fluorescent into strongly fluorescent complexes

Fluorescence-time trace for the reaction ofthiol (RC6H4SH) with [AuCl(9)] in C2H4Cl2(c = 1.0·10-6 mol·L-1), and hünig base.

Systematic Modulation of the Fluorescence Brightness in Coumarin tagged

NHC-Gold-Thiolates

0 2 4 6 8 10 12 14 16 18 20 22 240,0

0,2

0,4

0,6

0,8

1,0

flu

ore

scen

ce i

ntn

esit

y a

t 554 n

m

time/ min

NMe2

OMetBu

Me

HCl

CF3

-1,0 -0,8 -0,6 -0,4 -0,2 0,0 0,2 0,4 0,6

-1,4

-1,2

-1,0

-0,8

-0,6

-0,4

-0,2

log

. re

l. f

luo

res

ce

nc

e i

nte

ns

ity

Hammett parameter

Equation y = a + b*x

Weight No Weighting

Residual Sum of Squares

0,03572

Adj. R-Square 0,94178

Value Standard Error

D Intercept -0,71435 0,03294

D Slope 0,79615 0,0804

OMe

NMe2

CF3

ClH

MetBu

350 400 450 500 550 600 6500

2

4

6

8

10

12

14

16

18

20

22

flu

ore

sc

en

ce

in

ten

sit

y a

t 4

56

nm

wavelength/ nm

7 min

4 min2.5 min

0.9 min

0.7 Min

0 1 2 3 4 5 6 7 8 9 10 11 12

0

2

4

6

8

10

12

14

16

18

20

22

flu

ore

sc

en

ce

in

ten

sit

y a

t 4

56

nm

time/ min

M= Rh

M=Ir

+ CO

Determination of Quantum Yield

Log (Relative fluor. intens.) vs

Hammett parameter plot for thereaction of [AuCl(9)] with different

para-substituted thiophenols.

Table 1. Fluorescence quantum yields of the azolium salts 9·HCl

and of the respective metal complexes.

Compound φ (QY) λabs [nm] λem [nm]

9·HCl 0.80 422 456

[AuCl(9)] 0.77 422 456

[Pd(allyl)Cl(9)] 0.41 422 456

[PdCl2(Cl-py)(9)] 0.06 422 456

[RuCl2(ind)(9)(SIMes)] 0.005 422 456

[IrCl(cod)(9)] 0.05 422 456

[IrCl(CO)2(9)] 0.29 422 456

[RhCl(cod)(9)] 0.016 422 456

[RhCl(CO)2(9)] 0.31 422 456

All compounds 9: lmax= 422 nm, lem= 456 nm, c= 1.0·10-6 mol·L-1

in 1,2-dichloroethane, standard coumarin 153

Synthesis of Coumarin tagged Azolium salt and respective Metal NHC Complexes

Synthesis of metal complexes : a) [AuCl(Me2S)], 9·HCl, K2CO3, 60°C, acetone; b) 9·HCl, [PdCl(allyl)]2 and

K2CO3 acetone, 60 °C, 4 h; c) PdCl2, 9·HCl, 3-Cl-pyridine solvent, K2CO3, 80°C, 24 h; d) 9·HCl, Ag2O, 40°C,CH2Cl2 then [(SIMes)RuCl2(ind)(py)], (ind= 2-phenylindene-1-ylidene), 60°C, toluene; e) [RhCl(cod)]2,

acetone, 60°C, 9·HCl, K2CO3 or [IrCl(cod)]2, CH2Cl2, 40°C, 3·HCl, Ag2O; f) CO, 30 min, rt, CH2Cl2.

Solution of [Rh(Cl)(cod)(9)] (1·10-4 M in

CH2Cl2), irradiated with broadband UV-

light. Left: exposed to the ambient

atmosphere. Right: exposed to pure CO

gas for 5 min.

Application of the developed CO Gas Sensor under UV-light