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 (PQPBF₄) and thienyl-substituted 2-phenylbenzo[ij]pyrido[2,1,6-de]dithieno[3,2-b:2′,3′-g]quinolizin-13-ium perchlorate (BPDTQClO₄), 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.