Nonlinear Absorption Spectrum in Perylene Derivatives

Nonlinear Absorption Spectrum in
Perylene Derivatives
S. L. Oliveira, D. S. Corrêa, L. Misoguti, Misoguti,
S. C. Zilio, Zilio,
and C. R. Mendonça
Instituto de Física de São Carlos-USP
Carlos USP
C.J.L. Constantino
Departamento de Física, Química e Biologia, FCT-UNESP,
FCT UNESP, Brazil
R.F. Aroca
Materials and Surface Science Group, University of Windsor, Canada

ABSTRACT
Knowledge about nonlinear absorption spectra of materials used in
photonic devices is of paramount importance in determining their optimum
operation wavelengths. In this work, we have investigated the two-photon
absorption (2PA) degenerate cross-section spectrum for perylene derivatives
using the Z-scan technique with femtosecond laser pulses. All perylene
derivatives studied present large 2PA cross-sections, only comparable to the
best ones reported in the literature. The results achieved in the present
investigation indicate perylene derivatives as promising materials for twophoton
applications.
S. L. Oliveira, D. S. Correa, L. Misoguti, Misoguti,
C. J. L. Constantino, Constantino,
R. F. Aroca, Aroca,
S. C. Zilio, Zilio,
C. R. Mendonça, Mendonça,
“Perylene “ Perylene
Derivatives with Large Two-photon Two photon Absorption Cross Sections for Application in Optical Limiting Limiting
and Upconversion
Lasing” Lasing”
Advanced Materials, in press (2005).

TWO-PHOTON TWO PHOTON ABSORPTION
Upon exposure to intense laser pulses, molecules can instantaneously instantaneously
absorb two photons to
access an excited state, each of them with half of the energy required required
to match the electronic
transition.
1-photon absorption
(Linear)
2-photon absorption
(Nonlinear)
r
P = χ
r
(
. E + χ
r r
(
: EE
+ χ
r r r
MEEE
+ ...
Such 2PA process has interesting characteristics, with direct consequence consequence
for applications:
(i) improved spatial resolution due to the square dependence on the excitation
irradiance → 3D optical data storage, micro-fabrication;
micro fabrication;
(ii) negligible linear absorption at the pumping wavelength, with with
the resulting increase of
penetration depth → photodynamic cancer therapy
( 1 )
2 )
[ ] ) 3 (
Im χ
α = α0
+ β I
3 )
ββ: two-photon two photon absorption coefficient

TWO-PHOTON TWO PHOTON ABSORPTION SPECTRUM
Accordingly, a great deal of effort was directed to the development development
of various design
strategies employed to synthesize new two-photon two photon absorbing materials with large 2PA
cross-sections cross sections ( (δδ ) and increase physical and chemical stability.
High optical nonlinearities have been reported in organic materials materials
at specific wavelengths,
only recently the dispersion of the nonlinear absorption over a wide spectral range started
to be characterized. Such information is important:
(i) Molecular design strategy of a given nonlinear optical material material
(ii) Origin of the observed nonlinearities
(iii) Operation wavelength for a given device
2PA spectrum is obtained from:
- Multi-photon Multi photon excited fluorescence
- Open-aperture Open aperture Z-scan Z scan
discrete wavelengths, tunable sources

OPEN-APERTURE
OPEN APERTURE Z-SCAN SCAN
( z)
( z,
0)
∞
∫
−∞
2
− [ 1+
q ( z,
0)
e ]
T 1
τ
TN(
z ) = = ln 0 dτ
LT π q
0
Laser
Normalized Transmitance
1.00
0.98
0.96
0.94
0.92
Normalized Transmittance:
Knowing that
0
Sample
0.90
-10 -8 -6 -4 -2 0 2 4 6 8 10
0
( ) 1 2 2 −
1+
z /
q ( z,
t ) = βI
( t ) L z
z
0
Photodetector
δ = hνβ N
M. Sheik-Bahae et al., IEEE J. Quantum Electron. 26, 760-769 (1990).
Trigger
EXPERIMENTAL SETUP
Clark-MXR
Lock-in
Photodetector
775 nm
z = 0
OPA
Sample
(Clark-MXR, CPA-2001)
775 nm; 150 fs 0.8 mJ; 1kHz
λ = 460-2600 nm
Spatial Filter
460-2600 nm; 120 fs; 20-60µJ
(TOPAS, Quantronix)

In this context, the present work reports on the degenerate 2PA cross-section cross section spectra of
perylene tetracarboxylic derivatives (PTCD) in the spectral range going from the visible
to the near infrared.
PTCD are organic dyes, readily available, thermal and chemically stable. The perylene
moiety presents remarkable electron donor characteristics, although although
adding lateral
groups the molecule could play the role of electron acceptor or donor. Moreover, their
strong absorption and emission in the visible spectral range makes makes
them potential
candidates for applications as photoconductors, laser materials, etc.
H11C5
N
C
N
N
C
C
O O
O
C
N
C
O
MOLECULAR STRUCTURES
N
C
N
N N
AzoPTCD Monothio BZP
PazoPTCD
N
C
N
C
O
H9C4
O
O
C
N
C
O
S
BuPTCD
N
O
O
C
N
C
O
C4H9

σ abs (10 -16 cm 2 )
6
4
2
0
4
2
0
3
2
1
0
3
2
1
TWO-PHOTON TWO PHOTON ABSORPTION CROSS-SECTION
CROSS SECTION
AzoPTCD
BZP
PazoPTCD
BuPTCD
12
9
6
3
0
6
0
300 400 500 600 700 800
0
900 1000
Wavelength (nm)
4
2
0
6
4
2
0
6
4
2
δ (10 3 GM)
FIG. 1. Linear absorption and degenerate 2PA
spectrum of the PTCD materials in a solution with
10% trifluoroacetic acid in dichloromethane.
- PTCD → linear absorption bands (400-660 (400 660 nm),
with the vibronic structure superposed to the π-π* *
transition.
- High δ values at several excitation wavelengths.
- The increase observed in the 2PA cross-section
cross section
spectra → resonance enhancement of the
nonlinearity ↔ sum-over sum over states (SOS) model,
assuming that the π→π* π→π transition gives the major
contribution to the virtual intermediate state and
that the excited state corresponds the absorption
peaks around 350 nm.

FRONTIER MOLECULAR ORBITALS
The molecular geometries were optimized by the AM1 method.
Frontier molecular orbitals were calculated using ZINDO/S (HiperChem
( HiperChem 7.5).
Configuration interaction (CI) calculations included single excited excited
configurations from the
ground state, 24 (occupied) x 24 (unoccupied)
Transition energy (∆E ( linear.abs)
linear.abs)
decreases in a similar way as the π-conjugation conjugation length;
Bathchromic shift are the result of the HOMO → LUMO energy change;
By analyzing the 2PA spectra far from linear absorption edge of the four PTCD derivatives
it can be established an unambiguous relation between molecular charge delocalization
(conjugation length) and the third-order third order nonlinear optical response (2PA):
The results suggest that even larger 2PA cross-sections cross sections could be obtained by
manipulating the perylene derivatives, by positioning donor or acceptor groups
symmetrically or by increasing the molecule conjugation length, length,
in agreement with the
molecular design strategies proposed in the literature.
M. Albota, Albota,
D. Beljone, Beljone,
J. L. Breda, Breda,
J. E. Ehrlich, J. Y. Fu, A. A. Heikal, Heikal,
S. E. Hess, T. Kogej, Kogej,
M. D. Levin, S. Marder, Marder,
D. McCord-Maughon
McCord Maughon, ,
J. W. Perry, H. Rockel, Rockel,
M. Rumi, Rumi,
G. Subramanian, W. W. Webb, X. L. Wu, C. Xu, Xu,
Science 1998, 1998,
281, 281,
1653.

HOMO:
LUMO:
AzoPTCD

HOMO:
LUMO:
Monothio BZP

HOMO:
LUMO:
PazoPTCD

HOMO:
LUMO:
BuPTCD

OPTICAL LIMITING
The result shows that PTCD compounds exhibit effective 2PA optical limiting action,
which is useful to limit very short pulses, pulses,
especially at wavelengths near the linear
absorption edge.
E output (µJ)
0.05
0.04
0.03
0.02
0.01
0.00
(a)
0.3
0.2
AzoPTCD
Monothio BZP
PazoPTCD
BuPTCD
(b)
Transmitância Normalizada
1.0
0.8
0.6
0.4
0.2
AzoPTCD
monothio BZP
0.0
-1.0 -0.5 0.0
x (cm)
0.5 1.0
0.00 0.03 0.06 0.09 0.12 0.15 0.18
E input (µJ)
∆T
0 5 10 15 20 25 30 35
FIG. 2. (a) Output energy as a function of input energy of AzoPTCD (10 18 molecules/cm 3 ) in a solution
with 10% TFA in DCM and placed in a 2-mm 2 mm thick quartz cuvette for excitation wavelength at 770
nm. The solid line represents the linear transmittance. The inset inset
shows open-aperture open aperture Z-scan Z scan signatures
for AzoPTCD and Monothio BZP; (b) Transmittance Transmittance
change as a function of irradiance for PTCD
derivatives
0.1
0.0
Irradiance (GW/cm 2 )

Normalized Fluorescence
2.0
1.5
1.0
0.5
UPCONVERSION EMISSION INDUCED BY 2PA
A strong two-photon two photon excited fluorescent emission, which is a relevant prerequisite prerequisite
for
upconversion lasing, was measured in PTCD for excitation at 770 nm. It should should
be pointed
out that the fluorescence is high enough to be seen by naked eyes. eyes.
AzoPTCD
Monothio BZP
PAzo
BuPTCD
Intensity (arb. units)
0.0
510 540 570 600 630 660 690 720
Wavelength (nm)
10 1
10 0
FIG. 3. (a) Normalized two-photon two photon excited fluorescent emission of the PTCD compounds in a solution solution
with 10% TFA in DCM pumped at 770 nm; (b) 2PA fluorescence intensity intensity
vs. incident energy.
10 2
10 1
slope ~ 2
(a) (b)
10 2
Incident power (µW)
The observed emission indicates the potential of PTCD to be used as active media for 2PP
laser operating at short wavelengths. The he efficiency of 2PP lasing in dyes reported so far
has been rather low (overall 2PP lasing efficiency smaller than 0.1).

CONCLUSIONS
In summary, large 2PA cross-sections cross sections were measured, which are in the same order of the
best ones reported for organic compounds specially designed for nonlinear absorption. absorption.
The
results support that 2PA cross-section cross section can be improved by molecular design strategies and
the resonance enhancement effect. It is expected that increasing the conjugation and/or
adding symmetric donor and acceptor species could further improve improve
the 2PA effect. Results
on the transmittance change versus excitation irradiance and the strong two-photon
two photon
induced fluorescence demonstrate that PTCD compounds are attractive attractive
for application in
optical limiting and 2PP upconversion lasing.
Acknowledgments