Nonresonant exponential amplification of the excited-state intramolecular proton transfer (ESIPT) emission has been investigated with the film of ESIPT dendrimer (QG2) by pico- and femtosecond laser experiments. The intrinsic four-level nature of ESIPT and the reduced concentration quenching by dendritic effect made QG2 film an optical gain medium with the threshold intensity lower than 20 μJ/cm2/pulse. The characteristics of emission amplification are discussed in terms of the amplified spontaneous emission (ASE) related with ESIPT.

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Tetrasubstituted indium or gallium phthalocyanines and their dimers bridged with various ligands were dispersed in a polymer thin film, which was spin-coated on silver thin film vacuum-evaporated on a glass slide. All-optical reflectance control was achieved by complex refractive index changes upon photoexcitation of phthalocyanines by nanosecond laser in such a guided mode geometry. They gave rise in less than ns pulse width, and a few to a few tens of microseconds decay characteristic to the lifetime of the excited triplet state. Repeated and reversible reflectance changes were achieved. Axially bridged phthalocyanine dimers showed almost the same photoresponses as monomers.