Optical absorption spectroscopy of strongly disordered J-aggregates: Control of off-diagonal disorder

It was shown that the low-frequency edge of the exciton absorption band of J-aggregates of 1-methyl-1'-octadecyl-2,2'-cyanine iodide (analogue of PIG) experiences a change from Gaussian to Lorentzian in frozen, binary DMF-H2O solution, upon decrease of water concentration. In a Langmuir-Blodgett fil m, the shape of the low-frequency edge of exciton absorption band was neith er Gaussian nor Lorentzian, in contrast. A model of diagonal and off-diagon al disorder in the molecular chains is proposed to explain the observed ban d shapes, based on selective solvation of amphiphilic molecules by water an d DMF solvent molecules.