Primary photochemical process in films of dichromated gelatin: a quantitative approach

The photochemical behavior of dichromated gelatin films is investigated on irradiation at 365 nm and 491.6 nm. Fourier transform infrared (FTIR) spect roscopy confirms the two-step reduction of chromium(VI) into chromium(III). Prior to the irradiation, the molar extinction coefficient epsilon Of chro mium(Vl) in the film is measured as a function of the pH of the starting so lution with the result that epsilon appears to be pH independent in the ran ge 2 to 10 contrary to what is observed in solution. Chromium(V) resulting from a charge transfer between the polymeric matrix and chromium(VI) specie s in the excited state appears to be surprisingly stable in the gelatin mat rix. Accordingly, the subsequent slow reduction of chromium(V) into the fin al chromium(III) does not interfer in a significant way in chromium(VI) red uction. As a result, it is possible to determine the UV-visible spectrum of chromium(V) and to quantify its formation. So far no quantitative results were reported in the literature concerning the chromium(V) spectrum and its formation in a film of dichromated gelatin. FTIR spectroscopy confirms the two-step reduction of chromium(Vl) into chromium(lll). (C) 2000 society of Photo-Optical Instrumentation Engineers. [S0091-3286(00)01403-3].