Degeneracy, orientational disorder and chromophore size effects on Frenkelexcitons in columnar mesophases

The properties of Frenkel excitons in columnar mesophases are analysed usin g numerical calculations with a particular emphasis on the off-diagonal dis order induced by rotation of the molecular disks around the column axis. Th e influence of degeneracy of the molecular electronic transitions and the e ffect of the chromophore size are illustrated by means of the extended dipo le model. The localisation/delocalisation behaviour of the exciton states i s characterised by calculation of the participation ratio. It is shown that the existence of two orthogonal dipolar transitions per chromophore makes the optical spectra less sensitive to chromophore rotation and maintains th e eigenstates bearing the oscillator strength quite delocalised, even in th e presence of complete orientational disorder. (C) 2001 Elsevier Science B. V. All rights reserved.