Charge-transfer absorption in doped columnar liquid crystals

Abstract

The optical properties of doped columnar phases formed either by a 1 : 1 mixture of an electron donor [2,3,6,7,10,11-hexa-(n-pentyloxy)triphenylene] and an electron acceptor (2,4,7-trinitrofluoren-9-one) or by a dimer in which the donor (triphenylene moiety) and the acceptor (trifluorenone moiety) are covalently linked are reported and compared with those of the solutions. In concentrated solutions a charge transfer (CT) absorption is observed for both donor–aceptor pairs corresponding to 2.51 and 2.43 eV, respectively. For the 1 : 1 mixture, CT complex formation in solution is greatly favoured by the presence of molecular aggregates. The polarized absorption spectra obtained with oriented thin films reveal that the charge transfer occurs along the alternate donor–acceptor stacking.