Elektronische und sterische Substituenteneinflüsse auf die UV/VIS‐Absorptionsspektren der Phenylfulgidisomeren

Abstract

Electronic and Steric Substituent Influences on the U.V./VIS‐Absorption Spectra of Phenylfulgide Isomers The u.v./vis spectral data of a large number of phenylfulgides (E‐, Z‐, E‐E‐, E‐Z‐, Z‐E‐, Z‐Z‐isomers, 1.8a‐dihydronaphthalenes) are presented. An increase of the number of phenyl rings as well as substitution of the phenyl rings cause correlatable bathochromic spectral shifts. Steric influences became obvious by introducing methyl groups, by coplanarization of phenyl groups and in the series of isomers. By means of PPP calculations shifts in position and/or intensity of absorption bands are ascribed to the substituent effects. The calculated band polarization of E(E‐E)‐isomers are in agreement with the results of polarization spectra in oriented liquid crystal mesophases. The polarization spectra allow the assignment of the longwave absorption band to the S 2 ← S 0 and S 1 ← S 0 electronic transitions for E‐E‐Isomers with a C 2v ‐symmetry.