Knowledge Bank

The absorption spectra of polycrystalline films of a number of photoconductive dyes have been measured and corrected for selective reflectivity. A comparison of the extinction coefficients and oscillator strengths of the same dyes in the solid state and in solution shows: (1) A general correspondence between the main singlet-singlet bands in the films and in solution. (2) A general decrease in oscillator strength in the solid, amounting to $30$ in different dyes, which cannot be accounted for by molecular orientation within the film and which is presumably due to molecular interaction. (3) An apparent broadening of the lowest-lying transitions in the films, which is due to a splitting of this band into two approximately equal components, separated by $0.1-0.3$ c.v., each having about the same shape as the solution peak. In addition, there is evidence for the better known ""polymer bands"" on the short-wave side of these peaks. Cooling to $77\circ K$ does not effect the spectra. The spectra of various dyes will be presented with a brief interpretation of some of the results.