Nonlinear optical properties of systems based on (tetra-15-crown-5- phthalocyaninato)indium(III)

The nonlinear optical properties of solutions of (2,3,9,10,16,17,23,24-tetra-15-crown-5-phthalocyaninato)indium(III) [(15C5)4Pc]In(OH) in tetrachloroethane (TCE) have been studied by the z-scan method. It has been found that a nonlinear optical response is due to supramolecular associates formed in a tetrachloroethane solution by heating to 90°C/slow cooling to room temperature cycling. The formation of the supramolecular associates has been studied by atomic force microscopy (AFM) and electronic absorption spectroscopy (EAS). It has been shown that a single thermal treatment of [(15C5)4Pc]In(OH) solutions in TCE results in the predominant formation of dimers, as evidenced by both a short-wavelength shift of the Q-absorption band of the monomeric complex (λmax = 692 nm) to the band of λmax = 653 nm and height doubling of molecular entities as measured by AFM. The dimers are responsible for the two-photon absorption measured in the femtosecond range, which has a relatively high cross section of σ2 = 1.38 × 10−46 cm4 s/(molecule, photon) or 1.38 × 104 GM. According to the AFM data, three cycles of heat treatment of the solution leads to the formation of supramolecular assemblies of about 200 nm length. The optical spectrum exhibits long-wavelength absorption at λmax = 841 nm and the long-wavelength edge near 1300 nm. In the case of nanosecond 1064-nm laser irradiation, the linear absorption S0 → S1 is primary, having the cross section of σ0 = α0/N = 2.3 × 10−20 cm2. The known high quantum yield (close to unity) of triplet states of indium phthalocyanines suggests that the main nonlinear optical effect is determined by intersystem crossing S1 → T1 and triplet-triplet absorption T1 → T2. The absorption cross section is σT-T = 1.14 × 10−19 cm2.