Spectroscopic characteristics of 9-cyanoanthracene mixed with polymethyl methacrylate and stearic acid in Langmuir–Blodgett films Somobrata Acharya a , D. Bhattacharjee b , G.B. Talapatra a, * a Department of Spectroscopy, Indian Association for the Cultivation of Science, Jadavpur, Calcutta 700 032, India b Department of Physics, Tripura University, Tripura, Agartala 799 130, India Received 25 June 2001 Abstract Multilayers of 9-cyanoanthracene (CNA) mixed with stearic acid (SA) as well as also polymethyl methacrylate (PMMA) at different mole fractions of CNA have been transferred onto quartz substrate to form stable Langmuir– Blodgett (LB) films. Surface pressure versus area per molecule isotherms confirms the formation of stable films. The absorption and fluorescence spectra of CNA–SA and CNA–PMMA mixed LB films were compared. In case of CNA– SA mixed LB films, even at very low mole fraction of CNA, aggregation was formed. While in case of CNA–PMMA mixed LB films, at very low mole fraction of CNA, no aggregation was formed. However with increasing mole fraction of CNA in PMMA formation of aggregate started which is indicated by the development of a new band in the ab- sorption spectra. At higher concentration this band overlaps with the high energy band to form a broad band profile in the absorption spectra. Steady-state fluorescence spectra also confirm these phenomena. Ó 2002 Published by Elsevier Science B.V. 1. Introduction 9-Cyanoanthracene (CNA) molecule is one of the several substituted anthracenes, having a well- known structured fluorescence spectrum exhibiting remarkable sensitivity to the microenvironment [1,2]. It has a quasi one-dimensional mirror sym- metric stacks of molecules packed face to face with a cis-orientation with respect to the CN-group. Intermolecular spacing of 3.93  A along the stack axis in the crystal lattice favors excimer formation involving an excited state association of a pair of cis-oriented molecules along the stack axis [3]. Steady state and time resolved fluorescence studies in the polycrystalline film of CNA at 77 K shows two types of excimeric emission with trans- and cis-configuration [1,2]. Langmuir–Blodgett (LB) technique of obtain- ing thin films allows the formation of organized assembly of molecules whose packing can be ma- nipulated at the molecular level by varying various parameters [4]. CNA, a non-amphiphilic molecule, cannot form stable LB film. However, when mixed 6 February 2002 Chemical Physics Letters 352 (2002) 429–434 www.elsevier.com/locate/cplett * Corresponding author. Fax: +91-3-34732805. E-mail address: spgbt@mahendra.iacs.res.in (G.B. Tala- patra). 0009-2614/02/$ - see front matter Ó 2002 Published by Elsevier Science B.V. PII:S0009-2614(02)00005-2