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We present a novel type of Langmuir trough which enables the study of monolayers deposited at the immiscible liquid/liquid interface under controlled surface pressure. Isotherms of phospholipids have been obtained both at the air/water and, for the first time, at the water/1,2-dichloroethane interfaces. The latter isotherms did not show well-defined plateau regions or phase transitions, probably due to the small size of the 1,2-dichloroethane molecules, which makes them very mobile in the surface phase. It was possible to keep the surface pressure of the monolayers constant for at least 0.5 h, which means that they can be used for electrochemical experiments, for example for the study of the kinetics of charge transfer across such monolayers.

Novel types of donor-acceptor (DA) molecules, consisting of covalently linked pyropheophytin-anthraquinone (PQ and ZnPQ) and phytochlorin-anthraquinone (PCQ and ZnPCQ) dyads and their diastereomers were studied by means of steady-state and time-resolved fluorescence and absorption spectroscopies. Conformational properties were found to play an important role in understanding the observed photochemical behavior of the flexible diastereomers PQ1,2 and ZnPQ1,2 DA dyads. The more compact conformers undergo fast (in a few picoseconds or less) light-induced electron transfer (ET) from the singlet excited state. The most extended conformers, however, possess a separation between the donor and acceptor, which is too long to allow relaxation of the singlet exited state via ET. A fast conformational exchange between the open and folded conformers was observed in a variety of solvents and was found to be crucial for the observed electron-transfer properties of the flexible DA dyads studied. The more rigid DA systems, PCQ and ZnPCQ, exhibited electron-transfer properties that could well be elucidated in the frame of the Marcus theory.

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