Large static dipole moment in substituted polyacetylenes obtained by electroabsorption

Changes in static dipole moment and polarizability upon electronic excitati on are determined from electroabsorption spectra of unoriented substituted polyacetylenes: poly[(o-isopropylphenyl)acetylene] (PPPA) and poly[[(o-trim ethylsilyl)phenyl]acetylene] (PMSPA). The electroabsorption spectrum agrees well with the sum of the first and second derivatives of the absorption sp ectrum. The dominant contribution of the second derivative is interpreted b y the linear Stark effect induced by the permanent dipole moments, which ar e associated with the charge-transfer transition from the side groups of th e main chain. Large static dipole moment differences were obtained to be \D elta mu\ = 74 +/- 10 and 57 +/- 10 D for PPPA and PMSPA, respectively. (C) 2000 Elsevier Science B.V. All rights reserved.