Multilayer χ(2) films from porphyrin chromophores by LBK processing
Electrooptic films based on a new class of porphyrin chromophores with exceptionally large molecular first hyperpolarizabilities are being developed. These chromophores feature donor and acceptor groups linked to the porphyrin macrocycle at the 5- and 15-meso positions through intervening ethynyl moieties. We report herein preliminary results that describe the ambient temperature assembly of ordered, electrooptic films using the Langmuir-Blodgett-Kuhn (LBK) method. The facile formation of such films was made possible by the preparation of amphiphilic chromophores containing hydrophobic aliphatic substituents to enhance the polar alignment at the air-water interface. Second harmonic generation and UV-Vis absorption were used to characterize the films as a function of the number of layers deposited. Polar films containing up to 10 layers were made by simple Y-type homolayer deposition, and up to six layers by the Y-type heterolayer method in which the porphyrin layers were interleaved with poly(t-butyl methacrylate). The polar order in these films relaxed exponentially (50% at room temperature after 3 weeks). Ionic structures are recommended for improved stability.
