Aggregation phenomena in photobicyclised pyridinium salts

The possible formation of aggregates in a solution of two planar heterocyclic salts, 2-phenylbenzo[8,9]quinolizino[4,5,6,7- fed ]phenanthridinylium tetrafluoroborate (PQPBF 4 ) and thienyl-substituted 2-phenylbenzo[ ij ]pyrido[2,1,6- de ]dithieno[3,2- b :2′,3′- g ]quinolizin-13-ium perchlorate (BPDTQClO 4 ), was investigated in organic solvents and in water, by the analysis of their UV-Vis and fluorescence spectra. The results provided evidence for the formation of H-aggregates in water, a conclusion supported by theoretical calculations of the transition energies of the cationic monomers (PQP + and BPDTQ + ) and of the dicationic π-stacked H-dimers in water.