THE QUANTUM EFFICIENCY OF DYE‐INDUCED PHOTOELECTRIC EFFECTS IN BILAYER MEMBRANES

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Abstract
Abstract— Voltage transients are generated across lipid bilayer membranes by light flashes as a result of photophysical processes in sorbed dyes which displace electrical charges. A theory is presented which indicates that: (i) the fraction of sorbed dye which displaces charge from one flash can be determined by the fractional reduction in the photovoltage amplitude resulting from a second and identical flash, providing the second flash occurs before dye excited by the first flash returns to its equilibrium condition. (ii) The photoeffect quantum efficiency can be determined from the fraction of dye displacing charge, the light intensity and the dyes' optical absorption cross section. Apparatus constraints required different experimental procedures for dyes with different excited state life times, which are discussed. Experimental results are presented for an azo dye, 3,3'‐bis(α‐(trimethyiammonium)methyl)azobenzenebromide (Bis‐Q), three carbocyanine dyes in the series 3,3'‐dimethyl‐2,2'‐oxacarbocyanine‐iodide (diO‐C1‐3), an amino‐pyridinium dye, 4‐(p‐(dimethyl‐amino)styryl)‐1‐rnethyl‐pyridinium‐iodide (di‐1‐ASP), and a xanthene dye, 2',4',5',7'‐tetraiodofluorescein (erythrosin), the sodium salt of which is known as F, D and C red number 3. The dyes' optical absorption cross section values are uncertain owing to solvent and orientational effects in membranes. Photoeffect quantum efficiency values obtained by calculating optical absorption cross sections from the dyes' molar extinction coefficients in aqueous solutions are: Bis‐Q (0.08), diO‐C1‐3 (0.31), diO‐C2‐3 (0.22), diO‐C5‐3 (0.08), di‐l‐ASP (0.3) and erythrosin (0.39).

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