3 October 1996 Studies on the H-aggregation in hemicyanine Langmuir-Blodgett films
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Abstract
We investigated the effects of deposition parameters, subphase additions and annealing on the optical linear (absorption) and nonlinear (second harmonic generation) properties of hemicyanine (HEM) Langmuir-Blodgett (LB) films via aggregate status variations. HEM molecules formed H- aggregates in LB films, characterized by a blue-shift of the absorption band relative to the monomeric spectra, leading to a reduction of the effective hyperpolarizability beta due to the second harmonic off-resonant effect. The spontaneous aggregation mainly occurred during compression on the Langmuir trough. The degree of H-aggregate could be reduced and beta could be enhanced by raising the compressional speed and/or lowering the deposition surface pressure. By adding KI in the subphase, the observed beta-enhancement and absorption band red-shift in HEM LB monolayers were attributed to H-aggregate dissociation and intramolecular charge transfer. The time-resolved fluorescence profiles of HEM LB multilayers showed that there mainly existed two species (monomer and dimer) with characteristic decay times in the order of 100 ps and 10 ps, respectively.
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Xingze Lu, Xingze Lu, Kui Han, Kui Han, Shihong Ma, Shihong Ma, Gongming Wang, Gongming Wang, Wencheng Wang, Wencheng Wang, } "Studies on the H-aggregation in hemicyanine Langmuir-Blodgett films", Proc. SPIE 2897, Electro-Optic and Second Harmonic Generation Materials, Devices, and Applications, (3 October 1996); doi: 10.1117/12.252931; https://doi.org/10.1117/12.252931
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