Synthesis and Properties of a Fully Conjugated Polydiacetylene: Poly(1,4-Bis (3-Quinolyl)-1,3-Butadiyne)
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SYNTHESIS AND PROPERTIES OF A FULLY CONJUGATED POLYDIACETYLENE: POLY(1,4-BIS (3-QUINOLYL)-1,3-BUTADIYNE). SATYA S. TALWAR, MANJUNATH B. KAMATH AND K. N. BABU Department of Chemistry, Indian Institute of Technology, Powai, Bombay, India 400 076. ABSTRACT Synthesis of a new fully conjugated polydiacetylene i.e. poly(1,4-bis(3-quinolyl)-l,3butadiyne) is described. Reflectance spectra ofpartiallypolymerised samples and the polymer are reported. The spectra show long wavelength absorption band at 750 nm. with the visible absorption edge above 800 nm. DC electrical conductivity measurements on pristine and Iodine doped Poly-DQ are reported. The results are discussed in terms of side group - backbone electronic interactions. INTRODUCTION Synthesis of new polydiacetylenes(PDAs) and study of their properties continue to be an active area of investigation[ 1]. Much of the recent interest in polydiacetylenes is related to their linear, nonlinear optical properties[2] and conductivity behaviour[3]. Polydiacetylenes exhibit one of the highest third order nonlinear coefficient and a fast response, which has potential applications in electro-optics and all optical communication system[4]. Polydiacetylenes have a highly conjugated S,, backbone consisting of an alternate sequence of single, double and triple bonds (Fig.l). Although electronic . .properties of these polymers are primarily dominated by R R/ R the i-conjugated backbone, the substituent pendant groups (R and R') markedly influence the electronic, FIG. I PDA CHAIN optical and other physical properties of polydiacetylenes. Polydiacetylenes are one dimensional semiconductors and their optical spectra are characterised by a sharp excitonic peak followed by an interband transition[3]. However the position of these spectral features is sensitive to the crystalline phase organisation of the substituent groups. An understanding of the nature and origin of these changes is relevant to design of suitable nonlinear optical materials[5]. Two kinds of substituent effects on the electronic and optical properties may be distinguished. Property changes may arise due to modifications in the geometry and planarity of the conjugated backbone induced by the crystalline phase organisation of the side group. Another kind of interaction becomes possible when the substituent group is in formal iconjugation with the backbone. Such substituents could affect the spectral and electronic conduction properties through n-electronic interaction of the substituent group and the backbone[6]. Relatively few polydiacetylenes with substituent groups in formal it-conjugation with backbone have been reported. This has been partly due to lack of solid state reactivity in many precursor diacetylenes(DAs')[7,8]. Recently there has been considerable interest in synthesis and polymerisation of diacetylenes with X-conjugating groups. Some success in synthesis of such PD As' and study of their properties have been reported[ 1,6,9,10]. n-conjugating substituent
Mat. Res. Soc. Symp. Proc. Vol. 173. ©1990 Materials
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