2005 Conference on Lasers and Electro-Optics Europe

Two-photon Absorption Spectrum in Perylene Derivatives

S. L Oliveira, L de Boni, D. S. Correa, L. Misoguti, S. C. Zilio, and C. R. MendonvaInstituto de Fisica de Sao Carlos, Universidade de Sao Paulo, Caixa Postal 369, 13560-970,Sdo Carlos, SP, Brazil

corresponding author: samoliveira@ifsc. usp.br

C.J.L. ConstantinoDepartamento de Ffsica, Qulmica e Biologia, FCT-UNESP, CP 467, 19060-900, Presidente Prudente, SP, Brazil

R.F. ArocaMaterials and Surface Science Group, University of Windsor, Windsor, On. N9B 3P4 Canada

Perylene tetracarboxylic derivatives (PTCD) are organic dyes and pigments well known for their electrical andoptical properties such as strong absorption and emission in the visible region. The mentioned characteristics makethem important candidates for applications as organic semiconductors, and laser materials. The possibility of make useof these materials in the nonlinear optics field would satisfy the intense search for organic compounds presenting highnonlinear optical absorptivities. The two-photon absorption (2PA) process is the subject of a fast-growing interest indifferent fields, such as chemistry, photonic and biological imaging. The measurement of spectrally resolved nonlinearoptical properties is very important in the viewpoint of molecular design and photonic materials. In this context, thiswork reports on degenerate nonlinear absorption spectrum from 725 to 1000 nm for bis (n-butylimido) perylene(BuPTCD), bis (benzimidazo) perylene (AzoPTCD), bis (benzimidazo) thioperylene (Monothio BZP), and n-pentylimido-benzimidazo perylene (PAzoPTCD) solutions.

Nonlinear optical measurements were carried out with the Z-scan technique, which is a simple and sensitive methodto determine the 2PA cross-section values. In our open aperture Z-scan experiments were employed laser pulses froman optical parametric amplifier pumped by 150 fs pulses at 775 nm delivered by a commercial Ti:sapphire chirped pulseamplified system, operating at I kHz repetition rate. The FWHM pulse duration was 120 fs, and the spatial profile ofthe laser beam presented a Gaussian distribution.

.3 -o-PrCD .5- (a) - Monothio BZP 70- (b) oAzoPtTCD

. . PazoPTCD o -o-Monothio BZPoBuPTCD 60 --PazPT'CD

4 0~~~~~~~~~~~~-BuPTCD0 50-

3 -n40-13~~ ~ ~ ~ o0 0

~20-Oo 10o

400 500 600 700 800 750 800 850 900 950 1000x (nm) x (nm)

Fig. 1. (a) Linear absorption spectr and (b) 2PA degenerate absorption spectra for PTCD derivatives

Fig. la shows the electronic linear absorption spectra of the PTCD derivatives investigated. The open aperture Z-scan signatures for the PTCD compounds as a function of wavelength were obtained in order to determine 6 in severalwavelengths. Nonlinear optical measurements were made under non-resonant excitation. The obtained values of the2PA cross-section for perylene compounds as a function of input wavelength are summarized in Fig. lb. All perylenederivatives present 6 values comparable to very large ones reported in the literature for different organic compounds.Preliminary studies indicate that the high S values achieved in these materials at wavelengths near to linear absorptionedge are related to the resonance enhancement effect described by SOS theory. The 2PA mechanism was confirmed bythe linear dependence of the transmittance change amplitude, AT, on the laser irradiance obtained from Z-scanmeasurements and the square dependence of the 2PA fluorescence emission intensity versus incident power at 780 nm.

In summary, large 2PA cross-sections were found, values comparable to the best ones presented in the literature fororganic compounds specially designed for nonlinear absorption. These results open a new window of opportunities bydemonstrating that within the class of PITCD materials there are molecules with unusually large 2PA cross-section.Therefore, a new class of materials for potential application in two-photon imaging and sensitization is presented. It isimportant to emphasize that the PTCD derivatives are easily available by means of simple synthetic paths and offerthermal stability and chemical inertness as well as strong linear absorption and fluorescence.

0-7803-8974-3/05/$20.00 ©2005 IEEE 327