Universita’ della Calabria
Dipartimento di Chimica
LASCAMM


Unità INSTM della Calabria
CEMIF.CAL
Cyclometallated Photoconductors:
Attractive Complexes
for
Optoelectronic Applications
Dr. Nicolas Godbert
New Class of Photorefractive Materials
AZPON
BEPON
O(CH2)5CH3
O(CH 2)5CH3
N
N
N
O
Pd
O
Pd
N
(CH2)5CH3
Dissolved in PIBMA (60 %)
J. Am. Chem. Soc, 2001, 5598-5599
N
(CH2)5CH3
Amorphous State
Efficiency max around Tg: 24ºC
Adv. Mater., 2002, 1233-1236
Photorefractivity
Photogeneration
Transport
Trapping
Space Charge Field Induction
Refractive Index Modulation
Photorefractive
Photoconductors
INVESTIGATIONS
TOWARDS IMPROVEMENTS OF PHOTOCONDUCTION
Photogeneration
Should depends on chemical Structure of the compounds
Charge Mobility: Holes or Electrons
Should depends on chemical structure (HOMO/LUMO)
and the physical organization of the material
Selected Materials
O(CH2)5CH3
O(CH 2)5CH3
N
N
N
O
Pd
N
Pd
N
BEPON-Pd
N
N
O
Pt
(CH2)5CH3
AZPON-Pt
(CH2)5CH3
PYPON-Pd
O(CH2)5CH3
N
O
Pt
N
N
O(CH2)5CH3
O(CH2)5CH3
N
O
(CH2)5CH3
(CH2)5CH3
AZPON-Pd
N
O
Pd
O(CH2)5CH3
N
(CH2)5CH3
BEPON-Pt
O
Pt
N
(CH2)5CH3
PYPON-Pt
Absorption
-1
O(CH2)5CH3
N
O
Abs
Pd
N
(CH2)5CH3
Photoconduction
300
At 300 nm
400
500
Wavelength (nm)
At 330 nm
High absorption
/I (S cm W )
Photoconduction of 1 micron thick film
600
At 450 nm
If < 0.1 Io
Low absorption
Photoconduction Palladium vs. Platinum
lmax: 460 nm
-1
/I (S cm W )
Photoconduction
Abs
Abs
-1
/I (S cm W )
lmax: 470 nm
Photoconduction
Absorption
Absoprtion
450
500
550
600
450
Wavelength (nm)
500
550
600
Wavelength (nm)
Pypon Pd: 6.9 mm thick film
Pypon Pt: 7.2 mm thick film
-1
/I(S cm W )
1E-8
1E-9
1E-10
Difference of
2 orders of magnitude
PYPON-Pt (470 nm)
PYPON-Pd (460 nm)
1E-11
1E-12
1E-13
0
10
20
30
40
50
E (V/mm)
60
70
80
PHOTOGENERATION
LUMO
Schiff Base Moiety
HOMO
Cyclometalated Moiety
AZPON
HOMO
LUMO
PYPON
HOMO
LUMO
BEPON
PHOTOGENERATION
HOMO/LUMO localisations
OMe
N
N
O
Pd
OMe
O
N
N
Me
HOMO/LUMO distribution space separated
LUMO situated on the Cyclometalated Moiety
HOMO situated on the Schiff Base Moiety
Pt
N
Me
A comparison between
S0 and S1 geometries
Twisted Excited State
PHOTOGENERATION
Structural Properties: Palladium versus Platinum
Quantum Efficency %
Quantum Efficiency
of Photogeneration
BEPON-Pt
BEPON-Pd
100
l : 533 nm
10
1
Intrinsec
photoconduction
0,1
0,01
Oc6H13
• Neglecting trapping
• Weak Absorpion
1E-3
N
O
M
1E-4
N
1E-5
C6H13
1E-6
0
2
4
6
1/2
Electric Field
8
10
1/2
(V/mm)
•
E. Hendrickx, et al, J. Chem. Phys., 112, 9557 (2000).
METAL ROLE: ELECTRONIC TRANSITIONS
BEPON-Pd
UV-Vis Spectrum Deconvolution
METAL ROLE: ELECTRONIC TRANSITIONS
Jablonski
Electronic Level
Diagram
Probable Intersystem Crossing
METAL ROLE: ELECTRONIC TRANSITIONS
Singlet States
Intersystem Crossing (ISC)
Triplet States
Absorption
Fluorescence
non-Radiative Decay
Phosphorescence
photon
Ground State
ISC probability increases with the Z4
ZPd= 46
ZPt = 78
EMISSION DECAYS
BEPON-Pd
BEPON-Pt
lem: 466 nm
lem: 480 nm
15
INTENSITY (a.u.)
INTENSITY (a.u.)
Decay
Fit
t= ~ 4 ns
BEPON-Pt SOLUTION
Decay
Fit
10
SOLUTION
t= ~ 5 ns
5
0
20 25 30 35 40 45 50 55
20 25 30 35 40 45 50 55
TIME (ns)
TIME (ns)
lem: 566 nm
t= ~ 4 ns
215
220
225
230
TIME (ns)
235
Decay
Fit
INTENSITY (a.u.)
INTENSITY (au.)
lem: 538 nm
240
t= ~ 4 ms
100
102
104
106
TIME (ms)
108
FILM
110
MOBILITY: BEPON-Pd
Current (A)
Space Charge Limited Current
ISCLC = 9mCV2/8d3
1E-10
m= 1,3 10-9 cm2V-1s-1
@ 35 V/mm
1E-11
100
1000
Applied Voltage (V)
d = 10 mm
Towards Optoelectronic Applications
Tuning of Absoprtion Properties
Chemical Modifications on Ligands
From UV to near IR photoconduction
Increasing Mobility of charges
Control of material supramolecular organisation
Increasing Life Time of Excited States
e-
h
D
A
D+
Ae(h)
Tuning of Absorption Properties
O(CH2)5CH3
N
4
3
O
Pd
Bepon
Azpon derivative 1
Azpon derivative 2
Azpon derivative 3
Azpon derivative 4
OMe
N
N
N
O
Pd
N
(CH2)5CH3
ABS
(CH2)5CH3
Bepon
2
Azpon derivative 1
OMe
1
N
N
O
Pd
N
N
N
O
Pd
N
0
400
500
600
700
800
Wavelength (nm)
(CH2)5CH3
Azpon derivative 2 Azpon derivative 3
OMe
Tuning of the LUMO level: CM Ligand
Tuning of the HOMO level: Schiff Base
(CH2)5CH3
OMe
N
N
O
Pd
N
(CH2)5CH3
Azpon derivative 4
Increasing Mobility of charges
OC12H25
O
C12H25O
C12H25O
OC12H25
N
O
N
Pd
O
N
N
C12H25O
O
O
OC12H25
O
C12H25O
OC12H25
Abs of 2,4 micron thick film
Discotic ester linkage
Discotic ether linkage
2,5
2,0
1,5
1,0
0,5
0,0
400
500
600
700
wavelength (nm)
800
900
Pd
N
O
O
OC12H25
OC12H25
OC12H25
O
N
O
C12H25O
3,0
300
OC12H25
OC12H25
O
C12H25O
O
C12H25O
C12H25O
OC12H25
O
O
OC12H25
OC12H25
OC12H25
OC12H25
OC12H25
Increasing Life Time of Excited
States
Collaborating with Dr N. Bellec and Prof. D. Lorcy
University of Rennes I (France)
c
a
Me
N
O
S
S
Me
S
S
Me
b
Pd
O
Me
C
H
N
O
S
Cl
Pd
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
Dr. Mario Amati, Dr. Sandra Belviso and
Prof. Francesco Lelj,
Dr Nathalie Bellec and Prof. Dominique Lorcy
For funding !
LASCAMM
Unità INSTM della Calabria