Journal of Physical Chemistry A, Vol.103, No.19, 3657-3665, 1999
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 linked pyropheophytin-anthraquinone molecules (PQ1 and PQ2) and their Zn derivatives (ZnPQ1 and ZnPQ2) have been previously synthesized and studied in a variety of solvents. The compounds are retaining the chlorophyll phytyl tail, which makes them suitable for the Langmuir-Blodgett (LB) technique. The technique 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 means of time-resolved fluorescence spectroscopy and direct transient photovoltaics measurements. Tn 100% films, an intramolecular ET is strongly reduced as a result of intermolecular aggregation between the DA molecules. To prevent the aggregation, the DA compounds were placed in a matrix of soft lipids (e.g., lipids with unsaturated carbon chains) and methods to achieve uniform deposition of multilayer films were developed. The highest efficiency of the intramolecular ET was obtained for the multilayer films prepared by combining layers of ZnPQ1 in a Soya lipids matrix with dipalmitoylphosphatidic acid as the bottom and intermediate layers. The sign of the signals in the photovoltaics measurements and, therefore, the direction of the ET can be controlled by the deposition direction of the DA active layers.