SPECTROSCOPY AND TIME-RESOLVED PHOTOCURRENT RESPONSE IN ORDERED PORPHYRIN THIN-FILMS

Solid state absorption and emission spectra of a family of metalated octakis(beta-decoxyethyl)porphyrins (MODEP) exhibit substantial shifts from their solution phase maxima. The efficiency for production of photocurrent upon steady state irradiation of a thin film of ZnODEP and PdODEP in an indium tin oxide sandwich cell depends on the identity of the metal and does not correlate directly with the solution phase oxidation potentials of the series. The rate constants for the production of photocurrent in ZnODEP and PdODEP sandwich photocells under low-intensity (less than or equal to 0.5 mJ/pulse cm(2)) irradiation were k(app(1)) = 1.2 x 10(7) s(-1) (pulse = 0.17 mJ/cm(2)) and 4.6 x 10(7) s(-1) (pulse = 0.23 mJ/cm(2)), respectively, with a second fast, kinetically unresolved component (k(app(2)) > 2 x 10(8) s(-1)) being observed at high-intensity irradiation (>1 ml/pulse cm(2)) in both photocells. The photocurrent decays follow a biexponential rate profile, with fast rate constants of 3.3 x 10(5) and 5.9 x 10(4) s(-1) and slower rate constants of 3.7 x 10(4) and 8.2 x 10(3) s(-1), respectively. Both appearance and decay kinetics for the observed photocurrents in thin film cells depend on applied bias and on incident excitation energy. Spectra of trapped charges produced by steady state irradiation are reported.