Absorption and Fluorescence Spectra of Polydiacetylenes (4BCMU and 3BCMU) in Solution

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Abstract
Absorption and fluorescence spectra have been measured on soluble poly-diacetylenes (4BCMU, 3BCMU), having the side group R=n-BCMU (n-butoxy carbonyl methyl urethane, n=4, 3), in chloroform/n-hexane mixture solvents for various solvent compositions and temperatures. The observed features of the absorption spectra are interpreted by assuming that two types of the coil-to-rod conformational transition take place in the two distinct isomeric bond-structures, which presumably correspond to the acetylenic and butatrienic types, respectively. Experimental phase-diagrams are presented as functions of solvent composition and temperature. Fluorescence bands were observed in rod-like polymer solutions at low temperatures. It is suggested that these largely Stokes-shifted emission bands are due to the self-trapped π-π * excitons on the one-dimensional polymer chains.