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