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Semiconductor Physics, Quantum Electronics & Optoelectronics. 2008. V. 11, N 3. P. 292-302.
Optical properties of π-conjugated donor-acceptor systems
with controlled hyperpolarizability
Institute of Physics, National Academy of Sciences of Ukraine, 46, prospect Nauky, 03028 Kyiv, Ukraine; e-mail: yupiryat@iop.kiev.ua Abstract. For supramolecular compounds with donor and acceptor fragments, coupled with each other by the π-conjugated methyn chain, it was ascertained an influence of Cl and Br atoms on the π-conjugation and charge transfer in them in molecular and aggregate states. Compound, which contains Br atom, crystallizes into a noncentro- symmetric polar structure and under infrared (1064 nm) laser excitation it is observed the second harmonic generation and intense up-conversion photoluminescence in the visible spectral region. For compounds containing Cl atom, when passing into a crystalline state, only up-conversion photoluminescence is observed, which can be considered as two- photon excited. Possible mechanisms of intramolecular charge transfer and collective interactions in investigated molecular structures under one- and two-photon excitation are considered. Keywords: J-aggregate, H-aggregate, up-conversion photoluminescence, two-photon excited photoluminescence, molecular exciton, charge-transfer exciton.
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