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 p-stacked H-dimers in water.