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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: [email protected]
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