Photochemical electron transfer in monolayer assemblies. 2. Photoelectric behavior in chlorophyll a/acceptor systems

Abstract

A photoelectric effect has been observed in monolayer assemblies of chlorophyll and acceptor molecules deposited on a semitransparent aluminum electrode. The counterelectrode was mercury. With acceptors containing saturated side chains an open-circuit photovoltage of 150 mV and a short-circuit photocurrent of 34 nA cm-2 were detected across a load resistor. The quantum yield of electrons per photon was -2 X The current-voltage behavior was rectifying with a dark conductivity of -1.5 X 9-' cm-l. If acceptors with unsaturated side chains were used such as ubiquinone or plastoquinone ( I O mol % in stearic acid), the conductivity improved by a factor of IO. The open-circuit photovoltage now was 270 mV and the short-circuit photocurrent detected was 140 nA cm-2. The quantum yield was -2 X The reduction of the quinone group left the photoresponse unchanged. Similarly, the use of the polyisopropene squalene instead of plastoquinone left the photoresponse unchanged. The suggestion is made that the polyisopropene chain may be acting as "nature's molecular wire" making possible the tunnelling of electrons through lipid membranes and the maximum power conversion efficiency was -4 X and the maximum power conversion efficiency was -4 X

Photoinduced electron transfer across membranes

“…The promoting influence of molecules, containing long electron conducting polyene chains has also been observed for electron phototransfer across molecular monolayers [241]. Lehn and co-workers [242] have synthesized a series of molecular wires which are quite interesting from the point of view of transmembrane electron transfer.…”

PHOTOVOLTAIC EFFECT OF CHLOROPHYLL a–QUINONE SYSTEMS IN MULTILAYER ARRAYS

“…With 1. c 300 f l00A and y = 0.84 for Chla in multilayer array, it seems that our Chla photovoltai'c cells conform to the general behaviour of porphyrin and phthalocyanine films too. However, Janzen and Bolton (1979) found a square dependence of the photocurrent upon the light intensity for a four monolayer Chl a cell and explain their results in terms of a triplet-triplet upconversion. This is certainly not the general trend.…”

“…Following the same trend. Janzen and Bolton (1979) report that plastoquinone also increases the efficiency of photovolta'ic cells using an assembly of four chlorophyll a (Chl a ) t monolayers as the photoconductor, but they ascribe the effect produced by plastoquinone to the polyisoprene chain of the molecule. They also report that N,N-distearoyl-1,4-diaminoanthraquinone (SAQ).…”

Photoinduced Volta Potential in a Porphyrin Monolayer

“…The physical properties of the chromophore (Heeseman, 1980;Tancrede et al, 1981;Vandevyver et al, 1982;Heithier et al, 1983) or its photochemical stability (Aghion et al, 1981) in homogeneous phase have been widely investigated in the Langmuir films, but few studies deal with photodissociation (Hwang et al, 1977;Janzen and Bolton, 1979), charge transfer (Penner and Mobius, 1982) or photoelectron charge transfer (Sprintschnik et al, 1976). In this study we present evidence from Volta potential measurements for a photoinduced charge separation and stabilization at the interphase of an oxidizing subphase and a monolayer of the amphipathic basket handle zinc porphyrin P (compound No.…”