In this paper, we demonstrate that the irradiation of a metastable supersaturated lysozyme solution by a light produced by a continuous 150 W Xe lamp induces nucleation and that the mechanism is photochemically induced by a one-photon process. The irradiation of lysozyme molecules produces residual tryptophan radicals, which enhance the attractive interactions between molecules in solution, as shown by dynamic light scattering measurements, and increase the nucleation rate of lysozyme. When the intermediate is excited by visible light, the intermediate is converted into a permanently damaged species, and light-induced nucleation is inhibited, as shown by scavenger experiments (irradiation with two colors of excitation). These results suggest a new method for controlling nucleation and growth from metastable solutions that could be use in structural genomics and the pharmaceutical industry, for instance.

By use of electrostatic interactions of dye molecules and poly(diallyldimethylammonium chloride) (PDDA), the spin-coating technique has been successfully applied to the preparation of stable J-aggregate thin films of thiacarbocyanine dyes on a polycarbonate or quartz plate. The J-aggregate thin films were prepared by the spin-coating of PDDA aqueous solution on dye thin films prepared on a substrate by the spin-coating of 2,2,3,3-tetrafluoro-1-propanol solution of dyes. Photophysical properties of the dye thin films and J-aggregate thin films were studied by measuring the fluorescence spectra, quantum yields, and lifetimes. Coherent size of the J-aggregates was estimated to be 3-12 by means of the absorption bandwidth (full width at half maximum) or radiative lifetime. Photostability of the J-aggregate thin films was also studied in terms of photodegradation efficiency under argon and oxygen in comparison with the dye thin films, and J-aggregate thin films were found to be more stable than the corresponding dye thin films.