ELECTRONIC STATES OF MULTICHROMOPHORIC PHENYLETHYNYLBENZENE DERIVATIVES - EXCITON THEORY AND CS-INDO-CIPSI CALCULATIONS

The singlet electronic states of hexaphenylethynylbenzene derivatives are calculated combining S-CI calculations in the pi system and CS-IND O-CIPSI calculations in the sigma and pi systems (conformations spectr a-intermediate neglect of differential overlap-configuration interacti on by perturbative selected iterations). S-CI calculations (singly con figuration interaction) in the pi system using localized pi MOs on eac h chromophore are performed in order to characterize the nature (local ized or delocalized) of the excited states of these multichromophoric compounds. It is shown that simple considerations based on exciton the ory allow the prediction of these excited states. The effects of symme try lowering upon the spectroscopic properties of the hexaphenylethylb enzene derivatives arising from orientational disorder of the outer be nzene rings are compared to those arising from a methoxy substitution of the central aromatic core. The CS-INDO-CIPSI method, in a version r ecently modified by us, gives excellent results to interpret the elect ronic spectra of very large molecules. More generally, this theoretica l work provides directions concerning the way to modify the spectrosco pic properties of phenylethynylbenzene derivatives.