Synthesis and characterization of a new chromophor with acid/base-sensitive fluorescence emission Hai Guang Zhang a,b, * , Xu Tang Tao b , Kao Shan Chen c , Chun Xue Yuan b , Shi Na Yan a , Min Hua Jiang b a College of Chemistry Science, Qufu Normal University, Qufu 273165, China b State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China c School of Life Science, Shandong University, Jinan 250100, China Received 13 December 2010 Available online 24 June 2011 Abstract A new two-photon absorption compound, 2-{4-[(dicyanomethylidene-5,5-dimethylcyclohexl)vinyl]phenyl}imidazo[4,5- f][1,10]phenanthroline (DDVPIP), was synthesized and characterized. The one-photon excited fluorescence (OPEF) and two- photon excited fluorescence (TPEF) of DDVPIP are sensitive to the acid/base of the solution, which are enhanced in basic solution but weakened in acidic solution. Charge-transfer (CT) states of DDVPIP were calculated through theory methods to explain its acid/ base-sensitive fluorescent properties. # 2011 Hai Guang Zhang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Imidazo[4,5-f][1,10]phenanthroline; Two-photon absorption; Two-photon fluorescence Organic materials that can simultaneously absorb two photons have been extensively studied due to their increasing applications in optical power limiting, two-photon upconverted lasing, confocal imaging, photodynamic therapy, and three-dimensional optical data storage [1,2]. An important addition to those applications would be the development of two-photon sensors for biological applications [3,4]. Imidazo[4,5-f][1,10]phenanthroline (abbreviated as IP) derivatives and its metal complex has been demonstrated to be good emitters with interesting proton induced on-off emission switching characteristics through a reversible acid/base interconversion of imidazole group [5–8]. On the other hand, the isophorone-based dopant is an excellent red fluorescent material for organic light-emitting device (OLED) [9,10]. Here, a compound containing IP and isophorone was designed, which might be expected to be a fluorescent pH sensor. 1. Experimental The compounds 1,10-phenanthroline-5,6-dione [11], 2-(4-formylphenyl)imidazo[4,5-f][1,10]phenanthroline (fmp) [12], dicyanomethylidene-isophorone [9] were synthesized according to the literature methods. All other reagents were obtained commercially and used as supplied (see Scheme 1). www.elsevier.com/locate/cclet Available online at www.sciencedirect.com Chinese Chemical Letters 22 (2011) 1051–1054 * Corresponding author at: College of Chemistry Science, Qufu Normal University, Qufu 273165, China. E-mail address: haiguangzhang2006@126.com (H.G. Zhang). 1001-8417/$ – see front matter # 2011 Hai Guang Zhang. Publishedby Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2011.03.013