cyclometallated photoconductors: attractive complexes for optoelectronic applications dr. nicolas...
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Cyclometallated Photoconductors:
Attractive Complexes
for
Optoelectronic Applications
Dr. Nicolas Godbert
LASCAMM
Unità INSTM della Calabria
Universita’ della Calabria
Dipartimento di Chimica
CEMIF.CAL
NN
N
O(CH2)5CH3
(CH2)5CH3
OPd
AZPONAZPON BEPONBEPON
N
O(CH2)5CH3
(CH2)5CH3
OPd
N
Dissolved in PIBMA (60 %)
J. Am. Chem. Soc, 2001, 5598-5599
Amorphous State
Adv. Mater., 2002, 1233-1236
Efficiency max around Tg: 24ºC
New Class of Photorefractive Materials
Photogeneration Transport
Trapping
Space Charge Field Induction
Refractive Index Modulation
Photorefractivity
Photorefractive Photoconductors
INVESTIGATIONS TOWARDS IMPROVEMENTS OF PHOTOCONDUCTION
Charge Mobility: Holes or Electrons
Should depends on chemical structure (HOMO/LUMO)and the physical organization of the material
Photogeneration
Should depends on chemical Structure of the compounds
NN
N
O(CH2)5CH3
(CH2)5CH3
OPd
AZPON-Pd
PYPON-Pt
BEPON-Pd PYPON-Pd
AZPON-Pt BEPON-Pt
Selected Materials
NN
N
O(CH2)5CH3
(CH2)5CH3
OPt
N
O(CH2)5CH3
(CH2)5CH3
OPd
N
N
O(CH2)5CH3
(CH2)5CH3
OPt
N
N
O(CH2)5CH3
(CH2)5CH3
OPd
N
N
O(CH2)5CH3
(CH2)5CH3
OPt
N
300 400 500 600
Photoconduction
Absorption
Wavelength (nm)
Abs
/I (
S c
m W
-1)
Photoconduction of 1 micron thick film
High absorption Low absorption
At 330 nm
If < 0.1 Io
At 300 nm At 450 nm
N
O(CH2)5CH3
(CH2)5CH3
OPd
N
Photoconduction Palladium vs. Platinum
450 500 550 600
Ab
s
/I (
S c
m W
-1)
Wavelength (nm)
Photoconduction
Absorption
Pypon Pd: 6.9 m thick film
max: 460 nm
450 500 550 600
Abs
/I (
S c
m W
-1)
Wavelength (nm)
Absoprtion
Photoconduction
max: 470 nm
Pypon Pt: 7.2 m thick film
0 10 20 30 40 50 60 70 801E-13
1E-12
1E-11
1E-10
1E-9
1E-8
E (V/m)
/I(
S c
m W
-1)
PYPON-Pt (470 nm) PYPON-Pd (460 nm)
Difference of2 orders of magnitude
BEPONPYPON
HOMO HOMO LUMOLUMO
AZPON
HOMOCyclometalated Moiety
LUMOSchiff Base Moiety
PHOTOGENERATION
PHOTOGENERATION
HOMO/LUMO localisations
HOMO/LUMO distribution space separated
HOMO situated on the Schiff Base Moiety
LUMO situated on the Cyclometalated Moiety
NN
N
OMe
Me
OPd
N
OMe
Me
OPt
N
Twisted Excited State
A comparison between S0 and S1 geometries
PHOTOGENERATION
Quantum Efficiency of Photogeneration
: 533 nm
Structural Properties: Palladium versus Platinum
0 2 4 6 8 101E-6
1E-5
1E-4
1E-3
0,01
0,1
1
10
100
Electric Field1/2 (V/m)1/2
Qu
antu
m E
ffic
ency
%
BEPON-Pt BEPON-Pd
N
Oc6H13
C6H13
OM
N
• Neglecting trapping • Weak Absorpion
Intrinsec photoconduction
• E. Hendrickx, et al, J. Chem. Phys., 112, 9557 (2000).
METAL ROLE: ELECTRONIC TRANSITIONS
UV-Vis Spectrum DeconvolutionBEPON-Pd
16,33
0
5000
10000
15000
20000
25000
30000
35000
220 240 260 280 300 320 340 360 380 400 420 440 460 480 500 520 540 560 580 600 620 640 660 680 700 720 740 760 780 800
0
10
20
30
40
50
60
70
80
90
100e g1 g2 g4g5 g6 g7 g8g10 g12 g11 g9calc W/2+Lambda(max) Singlet lambdaTriplet rms
Jablonski Jablonski Electronic LevelElectronic Level
DiagramDiagram
METAL ROLE: ELECTRONIC TRANSITIONS
Probable Intersystem Crossing
Singlet States
Triplet States
Ground Statephoton
AbsorptionAbsorption
Intersystem Crossing (ISC)Intersystem Crossing (ISC)
FluorescenceFluorescence
PhosphorescencePhosphorescence
non-Radiative Decaynon-Radiative Decay
ZPd= 46 ZPt = 78
METAL ROLE: ELECTRONIC TRANSITIONS
ISC probability increases with the Z4
20 25 30 35 40 45 50 55
INT
EN
SIT
Y (
a.u
.)
TIME (ns)
Decay Fit
BEPON-Pd
= ~ 4 ns
20 25 30 35 40 45 50 55
0
5
10
15BEPON-Pt SOLUTION
INT
EN
SIT
Y (
a.u
.)
TIME (ns)
Decay Fit
BEPON-Pt
100 102 104 106 108 110
INT
EN
SIT
Y (
a.u
.)
TIME (s)
Decay Fit
= ~ 5 ns
= ~ 4 s
SOLUTIONSOLUTION
FILMFILM
215 220 225 230 235 240
INT
EN
SIT
Y (
au.)
TIME (ns)
= ~ 4 ns
em: 466 nm em: 480 nm
em: 538 nm em: 566 nm
EMISSION DECAYS
= 1,3 10-9 cm2V-1s-1
100 1000
1E-11
1E-10
Cu
rren
t (A
)
Applied Voltage (V)
ISCLC = 9CV2/8d3
@ 35 V/m
MOBILITY: BEPON-Pd
Space Charge Limited Current
d = 10 m
Towards Optoelectronic Applications
Tuning of Absoprtion Properties
Chemical Modifications on Ligands
Increasing Mobility of charges
From UV to near IR photoconduction
Control of material supramolecular organisation
Increasing Life Time of Excited States
D A D+ A-
e-
e(h)
h
Tuning of Absorption Properties
400 500 600 700 800
0
1
2
3
4
AB
S
Wavelength (nm)
Bepon Azpon derivative 1 Azpon derivative 2 Azpon derivative 3 Azpon derivative 4
N
O(CH2)5CH3
(CH2)5CH3
OPd
N
NN
N
(CH2)5CH3
OPd
NN
N
(CH2)5CH3
OPd
OMe
NN
N
(CH2)5CH3
OPd
OMeOMe
NN
N
(CH2)5CH3
OPd
OMe
Bepon Azpon derivative 1
Azpon derivative 2 Azpon derivative 3
Azpon derivative 4Tuning of the HOMO level: Schiff Base
Tuning of the LUMO level: CM Ligand
Increasing Mobility of charges
N
O
ONN
Pd
O
O
O
O
OC12H25
C12H25O
C12H25O
C12H25O
C12H25OOC12H25
O
OOC12H25
OC12H25
OC12H25
OOC12H25
OC12H25
OC12H25
N
OC12H25
ONN
Pd
O
O
OC12H25
C12H25O
C12H25O
C12H25O
C12H25OOC12H25
O
OOC12H25
OC12H25
OC12H25
OC12H25
300 400 500 600 700 800 900
0,0
0,5
1,0
1,5
2,0
2,5
3,0
Ab
s o
f 2,4
mic
ron
th
ick f
ilm
wavelength (nm)
Discotic ester linkage Discotic ether linkage
Increasing Life Time of Excited States
a bc
C
H
N
O
S
Cl
Pd
N
PdO
O
S
S
S
S
Me
Me
Me
Me
Collaborating with Dr N. Bellec and Prof. D. LorcyUniversity of Rennes I (France)
First Pd Complexe covalently linked to TTF donnor moiety
Acknowledgments
Prof. Mauro Ghedini and Prof. Attilio Golemme
Dr Roberto Termine, Dr. Mara Talarico and Dr Iolinda Aiello
LASCAMM
Unità INSTM della Calabria
For funding !
Dr. Mario Amati, Dr. Sandra Belviso and Prof. Francesco Lelj,
Dr Nathalie Bellec and Prof. Dominique Lorcy