The monolayer formation of a series of 2-substituted benzimidazoles at the air/water interface was studied by the measurements of surface pressure-area isotherms. Concentrated silver(I) ion in the subphase can induce the monolayer formation of 2-alkylbenzimidazole derivatives (BzCn) with the alkyl chain equal to or greater than C5 although the derivatives cannot form monolayers on pure water surface except BzC17. Similar behavior of monolayer formation of 2-phenylbenzimidazole was also observed. The measurements of UV spectra and X-ray photoelectron spectroscopy analysis of the transferred films suggested that such monolayer formation was fulfilled through an in situ formation of a polymeric silver(I)−benzimidazole complex at the air/water interface.

An equilibrium between triplet states, DT + A ¡=» D + AT, was directly observed by pulse radiolysis and laser photolysis techniques. It was demonstrated that the free-energy difference calculated from the equilibrium constant is equivalent to the difference in energy between the triplet states. The triplet energy of a solute can be determined by measuring the equilibrium between the triplet state of this solute and another triplet of known energy. Triplet energies thus obtained are (in eV) biphenyl, 2.93, m-teiphenyl, 2.88, and p-terphenyl, 2.66 which are higher than the phosphorescence energies and l,T-binaphthyl, 2.53 and l,2'-binaphthyl, 2.43 which agree with the phosphorescence energies. The triplet energy obtained by this method is considered to correspond to the nonvertical triplet energy.

Two-dimensional aggregation of a long-chain thiacarbocyanine dye 5,5‘-dichloro-3,3‘-dioctadecyl-9-ethylthiacarbocyanine perchlorate in the monolayers on subphases containing different synthetic polyanions were studied. The aggregation process of the dye in the monolayers was followed by the in situ measurement of the absorption spectra of the monolayers. Two J aggregates were observed at 648 and 666 nm in the monolayer on a plain water surface at all the surface pressures. On the subphase containing poly(acrylic acid), sodium (PAA), and poly(vinyl sulfonic acid), potassium salt (PVS) subphases, the J aggregates were formed at relative high surface pressures (15 and 17.5 mN/m, respectively). On the PVS subphase, an H aggregate at 472 nm was also observed at higher surface pressure (>40 mN/m). On the poly(styrenesulfonic acid), sodium salt (PSS) subphase, neither J nor H aggregates were observed even at higher surface pressures. Models were proposed to explain these interactions between the positively charged dye monolayers and polyanions.