Two-photon absorption and up-converted fluorescence of novel triphenylamine-based oligomers Wenlei Li a , Xiaomei Wang a, * , Wanli Jiang b , Ping Yang a , Yongli Yan c , Shixiong Qian c , Zhiming Wang a a Institute of Material Engineering, Chemistry Department, Suzhou University, Suzhou, China b State Key Laboratory of Crystal Materials, Shandong University, Jinan, China c Department of Physics, Fudan University, Shanghai, China Received 9 October 2006; received in revised form 9 October 2006; accepted 11 October 2006 Available online 6 December 2006 Abstract Three new conjugated oligomers (referred to as P1, P2 and P3), of ‘‘Dep-A’’ structure with the same donor group of 4-methyl triphenyl- amine but different acceptor groups such as naphthalene for P1, dibenzothiophene for P2, and dibenzofuran for P3, were synthesized and char- acterized. The linear optical properties, including absorption and one-photon induced fluorescence, fluorescence quantum yield (F) and lifetimes of the oligomers are reported. Two-photon absorption (TPA) properties were measured by open-aperture Z-scan techniques, while two-photon induced fluorescence (TPF) behaviour was recorded using a CCD spectrosensitometer, employing a Ti:sapphire femtosecond laser pulse. It was found that P1 displayed the greatest two-photon absorption coefficient (b) due to its larger intermolecular charge transfer and stronger interac- tions between donor and acceptor groups. In contrast, P3 exhibited strongest one- and two-photon fluorescence due to its dibenzofuran acceptor group possessing more preponderant radiation dynamics, in comparison with its dibenzothiophene- and naphthalene-based counterparts. Ó 2006 Published by Elsevier Ltd. Keywords: Two-photon absorption; Two-photon induced fluorescence; Dibenzothiophene; Dibenzofuran 1. Introduction Conjugated oligomers are important materials for applica- tion in two-photon induced fluorescence (TPF) microscopy that has gained widespread popularity in the biology commu- nity owing to its ability to image at high penetration depth in tissue with reduced photodamage. The key ingredients for efficient molecular TPF applications such as high resolution 3D microscopy, deep tissue-penetrating photodynamic therapy (PDT), 3D microfabrication, high-density optical data storage and optical power limiting [1e5], depend critically on the availability of materials that possess large TPA cross-section and high two-photon excited fluorescence (TPF). Numerous organic compounds have been investigated both experimentally and theoretically in order to understand the structureeproperty relationship of materials with strong TPA. For example, some one-dimensional dipolar systems, heteroaromatic ring systems, octupolar molecules, multibranched and dendrimer systems can effectively enhance TPA absorptivity [6e16]. Recently, we reported the TPA and up-converted fluorescence properties of some chromophores based on triphenylamine and hetero- fluorene units, whose two-photon fluorescence intensity and TPA cross-section are correlated to electron coupling between the individual branch and obvious excited charge redistribution [17e21]. In this paper, we report three, newly synthesized con- jugated oligomers with 4-methyl triphenylamine as donor group and naphthalene, dibenzothiophene or dithozofuran as acceptor group. To understand the influence of the different electron- acceptors upon photoluminescence properties, linear absorption/ emission spectra including fluorescence quantum yield (F f ) and * Corresponding author. Tel.: þ86 512 62092786; fax: þ86 512 67246786. E-mail address: xmwangsuda@sohu.com.cn (X. Wang). 0143-7208/$ - see front matter Ó 2006 Published by Elsevier Ltd. doi:10.1016/j.dyepig.2006.10.010 Dyes and Pigments 76 (2008) 485e491 www.elsevier.com/locate/dyepig