Excited State Absorption and Two-Photon Induced Fluorescence of Novel Organic Dyes Wenfang Sun 1 Department of Chemistry, North Dakota State University, Fargo, ND 58105-5516 Dmitri Martyshkin, Sergey Mirov Department of Physics, University of Alabama at Birmingham, 1300 University Blvd., Birmingham, AL 35294-1170 Xin-Jing Tang, Li-Zhu Wu, 2 Chen-Ho Tung Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing, 100101, P.R. China ABSTRACT Organic materials with large excited state and/or two-photon absorption are desired for numerous device applications, such as optical limiting, two-photon upconversion lasing, three-dimensional data storage, and two-photon photodynamic therapy. Dialkylamino styryl thiazolium/benzoxazolium compounds are interesting excited state and two- photon absorbers for these applications. In this work, the nonlinear transmissivity of trans-2-[p-(N-methyl-N- (hydroxyethyl)amino)styryl]-N-methylthiazolium iodide (MHAST), trans-2-[p-(N-ethyl-N-(hydroxyethyl)amino)styryl]- N-methylthiazolium hexafluorophosphate (EHAST), trans-2-[p-(N-methyl-N-(hydroxyethyl)amino)styryl]-N- methylbenzoxazolium iodide (MHASBO) at 532 nm has been studied using 6 ns laser pulses. The two-photon induced fluorescence of these compounds at 940 nm has also been investigated. At 532 nm, both MHAST and EHAST exhibit reverse saturable absorption, however, MHASB exhibit saturable absorption. At 940 nm, all of these compounds exhibit two-photon induced up-conversion fluorescence, and the fluorescence intensity varies when the chemical structure changes. These preliminary results suggest that the nonlinear absorption (excited state absorption or two-photon absorption) characteristics of these compounds vary at different wavelengths and vary when their chemical structure changes. Keywords: Excited state absorption, two-photon induced upconversion fluorescence, single photon fluorescence, dialkylamino styryl thiazolium/benzoxazolium compounds 1. INTRODUCTION In recent years, organic material with strong nonlinear absorption, especially excited state absorption and two- photon absorption are attracting extensive interest because of their potential applications in optical limiting, 1 two-photon upconverted lasing, 2,3,4 three-dimensional data storage, 5 and two-photon photodynamic therapy. 6 Extensive work has been reported on the excited state absorption of variety organic materials, such as indanthrone derivatives and oligomers, 7,8 porphyrins, 9,10 phthalocyanines, 11,12,13 and organometallic compounds. 14,15 However, the linear transmittance for these reverse saturable absorbers is significant less than unity, which is a disadvantage for optical limiting applications. To remedy this deficiency, researchers begin to pay special attention to two-photon absorbing dyes because of their high linear transmission in most of the visible spectral range. Dialkylamino stilbazolium iodide 16,17,18 and stilbene derivatives 19 have been extensively investigated during the past a few years, some of them exhibit enhanced two-photon absorption and are promising candidates for optical limiting, upconverted lasing, and three- dimensional data storage applications. 1 W. Sun: E-mail: Wenfang.Sun@ndsu.nodak.edu ; Phone: (701) 231-6254; Fax: (701)231-8831 2 L.-Z. Wu: E-mail: lizhuwu@yahoo.com Multiphoton Absorption and Nonlinear Transmission Processes: Materials, Theory, and Applications, K. D. Belfield, S. J. Caracci, F. Kajzar, C. M. Lawson, A. T. Yeates, Editors, Proceedings of SPIE Vol. 4797 © 2003 SPIE · 0277-786X/03/$15.00 204