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 -,9 cis -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.