Electroabsorption spectroscopy of distyrylbenzene derivatives P.A. Lane a, * , H. Mellor a , S.J. Martin a , T.W. Hagler b , A. Bleyer a , D.D.C. Bradley a a Department of Physics and Astronomy, University of Sheeld, Sheeld S3 7RH, UK b Los Alamos National Laboratory, Los Alamos, NM 87545, USA Received 14 April 2000 Abstract We have studied the linear and nonlinear optical properties of model oligomers based on trans,trans 0 -distyrylbenzene to investigate the eects of chemical modi®cation on the electronic structure of stilbenoid oligomers and polymers. Replacing the central para-phenylene ring with a meta-phenylene ring reduces the conjugation of the molecule and introduces disorder into the ®lm, which signi®cantly reduces Davydov splitting of the main absorption band. Alkoxy substitution of any of the phenylene rings red shifts the lowest energy absorption band and enhances the oscillator strength of a high-energy sideband. Absorption by aggregates, which is obscured by eects of scattering on the ab- sorption spectrum, is clearly revealed by electroabsorption spectroscopy. Ó 2000 Published by Elsevier Science B.V. All rights reserved. Keywords: Distyrylbenzene; Electroabsorption; Electronic structure; Symmetry; Substitution 1. Introduction Distyrylbenzene (DSB) and other stilbenoid molecules are widely studied materials in their own right [1] and as model compounds for under- standing the photophysics of analagous conjugated polymers [2]. Analysis of conjugated polymers is complicated by a distribution of conjugation lengths. As the hyperpolarizability varies with conjugation length, a distribution of conjugation lengths makes it dicult to have an unambiguous interpretation of experimental studies. Hence, it is advantageous to study a model compound with a well-de®ned conjugation length to explore the ef- fect of chemical modi®cation on state energies and the nonlinear susceptibility. In this paper, we have studied the eect of (i) replacing the central para- phenylene ring in DSB with meta-phenylene rings and (ii) alkoxy substitution on the electronic struc- ture of stilbenoid model compounds. A series of model compounds based on trans,trans 0 -para- distyrylbenzene (DSB) and trans,trans 0 -meta- distyrylbenzene (m-DSB) have been synthesized, and we have analysed their electronic structure by absorption and electroabsorption (EA) spectro- scopy. DSB possesses C 2h symmetry and its electronic states are labelled A g or B u . In contrast, m-DSB has C 2v symmetry, and corresponding symmetry labels for electronic states are A 1;2 and B 1;2 . Transitions between states of opposite parity are Chemical Physics 257 (2000) 41±49 www.elsevier.nl/locate/chemphys * Corresponding author. Hicks Building, Houns®eld Road, Sheeld S3 7RH, UK. Tel.: +44-114-222-3544; fax: +44-114- 272-8079. E-mail address: p.a.lane@sheeld.ac.uk (P.A. Lane). 0301-0104/00/$ - see front matter Ó 2000 Published by Elsevier Science B.V. All rights reserved. PII: S 0 3 0 1 - 0 1 0 4 ( 0 0 ) 0 0 1 4 6 - 4