HIGH-PRESSURE INVESTIGATION OF ABSORPTION-SPECTRA OF J-AGGREGATES

The spectral shift of J-bands under high pressure up to 60 kbar has be en investigated for J-aggregates of different cyanine dyes. Under cond itions where no J-band can be observed at normal pressure, J-aggregate s are formed at higher pressure. A red shift of absorption upon increa sing pressure was found with a linear dependence of line position on p ressure. The results can be explained by a change of dipolar coupling of monomer molecules in the aggregate due to decreasing center-to-cent er distances. The different pressure slopes of various aggregates are interpreted from their different aggregate structures. The monomer abs orption is also red-shifted under pressure, but the pressure dependenc e is quite different and can be described by a solvent shift. From the linear dependence, the dipole-dipole coupling energy J can be determi ned with a simple theory. The general applicability and limitations of this method are discussed. (C) 1996 American Institute of Physics.