Electronic states of multichromophoric phenylethynylbenzene derivatives: exciton theory and CS-INDO-CIPSI calculations

Abstract

The singlet electronic states of hexaphenylethynylbenzene derivatives are calculated combining S-CI calculations in the π system and CS-INDO-CIPSI calculations in the σ and π systems (conformations spectra-intermediate neglect of differential overlap-configuration interaction by perturbative selected iterations). S-CI calculations (singly configuration interaction) in the π system using localized π MOs on each chromophore are performed in order to characterize the nature (localized or delocalized) of the excited states of these multichromophoric compounds. It is shown that simple considerations based on exciton theory allow the prediction of these excited states. The effects of symmetry lowering upon the spectroscopic properties of the hexaphenylethylbenzene derivatives arising from orientational disorder of the outer benzene rings are compared to those arising from a methoxy substitution of the central aromatic core. The CS-INDO-CIPSI method, in a version recently modified by us, gives excellent results to interpret the electronic spectra of very large molecules. More generally, this theoretical work provides directions concerning the way to modify the spectroscopic properties of phenylethynylbenzen derivatives.