Semiconduction and Photoconduction Activation Energies of the Retinals

Abstract ‐The semiconduction and photoconduction currents through 1‐ml thick sandwich cells of all‐trans‐, 13‐cis‐, 11‐cis‐retinal‐, and 13‐cis‐retinal‐m‐nitroaniline‐hydrogen chloride were measured as a function of the temperature in both the crystalline and melted states. From the slopes of graphs of the log of the current against 1000/TGK, the activation energies for semiconduction and photoconduction were calculated using the conductivity equations for the band model. The results of the average semiconduction activation energy measurements fell into two categories: The first group has activation energies between 1.9 and 2.4 eV and includes crystalline all‐trans‐, 13‐cis‐,9cis‐retinal, and both crystalline and melted 13‐cis‐retinal‐m‐nitroanaline hydrogen chloride; the second group has activation energies between 3.1 and 3.6 eV and includes crystalline 11‐cis‐retinal samples shorted. The average photoconduction activation energy for crysalline 13‐cis‐ and 11‐cis‐retinal, being 0.25 and 0.24 eV respectively, were essentially identical within experimental error, whereas the same parameter for 13‐cis‐retinal‐m‐nitroaniline hydrogen chloride was considerably lower at 0.15 eV. All‐trans‐retinal was not measurably photoconductive and 9‐cis‐retinal was only slightly photoconductive.