Light-induced electron transfer in pyropheophytin-anthraquinone dyads: Vectorial charge transfer in Langmuir-Blodgett films

Novel types of donor-acceptor (DA) compounds, consisting of covalently link ed pyropheophytin-anthraquinone molecules (PQ1 and PQ2) and their Zn deriva tives (ZnPQ1 and ZnPQ2) have been previously synthesized and studied in a v ariety of solvents. The compounds are retaining the chlorophyll phytyl tail , which makes them suitable for the Langmuir-Blodgett (LB) technique. The t echnique enables one to prepare solid films capable of performing vectorial intramolecular light-induced electron transfer (ET). The DA compounds form stable monolayers on a water surface and the monolayers can be transferred onto a solid substrate. The ET properties of the LB films were tested by m eans of time-resolved fluorescence spectroscopy and direct transient photov oltaics measurements. Tn 100% films, an intramolecular ET is strongly reduc ed as a result of intermolecular aggregation between the DA molecules. To p revent the aggregation, the DA compounds were placed in a matrix of soft li pids (e.g., lipids with unsaturated carbon chains) and methods to achieve u niform deposition of multilayer films were developed. The highest efficienc y of the intramolecular ET was obtained for the multilayer films prepared b y combining layers of ZnPQ1 in a Soya lipids matrix with dipalmitoylphospha tidic acid as the bottom and intermediate layers. The sign of the signals i n the photovoltaics measurements and, therefore, the direction of the ET ca n be controlled by the deposition direction of the DA active layers.