Excited-state absorption and two-photon-induced fluorescence of novel organic dyes

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.