Microstructure of squarylium dye J aggregate films examined on the basis of optical behavior at low temperature

The microstructure of a spin-coated film of squarylium dye J aggregates is examined on the basis of the measurement of the optical properties and the third-order nonlinear optical susceptibility chi((3)) at low temperature. The absorption maximum of J aggregates shifted to lower energies as the film temperature decreased, while chi((3)) was independent of the temperature. The latter finding indicates that the coherent length of J aggregates is confined by a structural boundary rather than by phonons; consequently, the observed peak energy shift can be due to temperature-dependent conformational change of the aggregates. The small aggregation size may contribute to the ultrahigh-speed optical response of squarylium dye J aggregates. (C) 2002 American Institute of Physics.