The Quantum Efficiency of Dye‐induced Photoelectric Effects in Bilayer Membranes

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).

Monitoring Ternary Systems of C12E5/Water/Tetradecane via the Fluorescence of Solvatochromic Probes

“…To complement Prodan and Nile Red, we chose the hydrophilic dimethylaminostibazolium dye 4-Di-1-ASP (pyridinium, 4-(2-(dimethylamino)phenyl)-1-methyl, iodide). This dye has also been reported as having polarity- and viscosity-dependent spectroscopic behavior and has been used in work related to dye-induced photoelectric effects in bilayer membranes . Thus, this probe should report from the aqueous side of the water−surfactant−alkane boundary and Nile Red from the hydrocarbon side, while Prodan should partition throughout the ternary system.…”

How Does Light Absorption Intensity Depend on Molecular Size?

“…Also ignored in the derivation are internal reflection, scattering, and other surface and geometric effects (7), such as preferential orientation of molecules. It is usual to ignore these effects, although they can be significant in a variety of important biological, chemical, and industrial problems dealing with condensed phases, such as suspensions, membranes (8,9), and photographic emulsions (JO).…”

“…The probability Pk/ of transition for each chromophore molecule per unit time is | c; 12. For a distribution p (energy x time/volume) of radiation density over frequency, Einstein (12,13) showed that pki = bmP and Btl = (2n2e23 h Eq 2 rkl (9) where h is Plank's constant, and £o is the vacuum permitivity. 3 Transition moment **kl = j^rT,dr Each rotational-vibrational (rovibrational) transition k' -> T that contributes to the electronic absorption band for k / has a discrete and a definite intensity expressed by either Phr or Ekr.…”