Spectrochimica Acta Part A 77 (2010) 473–477 Contents lists available at ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa Fluorimetric and prototropic studies on the inclusion complexation of 3,3 ′ -diaminodiphenylsulphone with -cyclodextrin and its unusual behavior Muthu Vijayan Enoch 1 , Rajaram Rajamohan, Meenakshisundaram Swaminathan ∗ Department of Chemistry, Annamalai University, Annamalainagar 608 002, India article info Article history: Received 12 January 2010 Received in revised form 29 May 2010 Accepted 15 June 2010 Keywords: 3,3 ′ -Diaminodiphenylsulphone Prototropism -Cyclodextrin TICT Inclusion complex abstract The photophysical and photoprototropic properties of 3,3 ′ -diaminodiphenylsulphone (3DADPS) in aque- ous -cyclodextrin (-CDx) solution have been investigated using absorption and fluorescence spectral techniques. -CDx forms 1:1 inclusion complex with 3DADPS as revealed by steady state and time- resolved fluorescence spectroscopy. This inclusion complex formation was also confirmed by the FT-IR and SEM image analysis of solid complex prepared by co-precipitation method. The existence of twisted intramolecular charge transfer state and the unusual red shift observed during inclusion complexation were analyzed and discussed. The ground and excited state acidity constants in -CDx are reported. Based on the photophysical and photoprototropic characteristics of 3DADPS in -CDx, the structure of the 1:1 inclusion complex is proposed. © 2010 Elsevier B.V. All rights reserved. Molecular recognition is a phenomenon in which a ‘receptor’ or a ‘host’ molecule forms a stable complex with one or more ‘guest’ molecules through weak forces such as hydrogen bonds, van der Waal’s and electrostatic interactions. Of many important hosts, cyclodextrins (CDxs) have been widely used over the last decade [1]. Cyclodextrins are cyclic oligosaccharides of six to eight ,d-glucopyranose units (namely ,  and -CDx respectively). Sig- nificant interest centered on complexation by cyclodextrins is due to their binding ability on several organic molecules of different size and shapes [2]. Numerous studies on the photophysical and photochemical properties of organic guest species complexed with cyclodextrins have been reported [3–7]. Intrinsic, site-specific, fluorescent probes for understanding drug–protein interactions are of current inter- est [8–12] and the analysis of photophysical behavior of such molecules in cyclodextrin can give information about the correct choice among such probes. Diphenylsulphones have been reported to be pharmaceuti- cally important as antimalarial and antileprotic drugs [13] and their photophysical and photoprototropic properties have been reported [14]. Absorption and fluorescence spectral techniques ∗ Corresponding author. Tel.: +91 9842381967. E-mail address: chemres50@gmail.com (M. Swaminathan). 1 Present address: Department of Chemistry, Karunya University, Coimbatore. serve as tools for studying the effect of acidity on pharmaceuti- cally important compounds. The fluorescence and proton transfer characteristics of some amino substituted diphenyl, diphenylsul- phones, diphenylethers, fluorene and thiazole in -cyclodextrin have been reported from our laboratory [15–20]. . Generally organic fluorophores show a blue shift in fluorescence during inclusion complexation with -CDx. We observed an unusual red shift in both florescence maxima of 3DADPS during inclusion complexation. In this paper, we report the fluorescent and prototropic behaviors of 3,3 ′ -diaminodiphenylsulphone in -cyclodextrin. 1. Experimental 1.1. Materials and methods 3,3 ′ -Diaminodiphenylsulphone (Aldrich) and -CDx (S.D. Fine Chemicals) were used as received. The purity of 3DADPS was checked by obtaining identical fluorescence spectra at different excitation wavelengths. The absorption spectra were recorded on a JASCO model 7800 spectrophotometer. Fluorescence spectra were obtained from JASCO FP-770 spectrofluorimeter. Fluorescence life- times were determined using a time-correlated picosecond single photon counting spectrofluorimeter (Tsunami, Spectraphysics). pH values in the range of 2–6 were measured on an ELICO pH meter model LI-1OT. A modified Hammett’s acidity scale (using a H 2 SO 4 –H 2 O mixture) was used for making solutions 1386-1425/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2010.06.021