Photoconductivity inp-diiodobenzene

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Abstract
Castro and Hochstrasser1 have measured the singlet-triplet absorption spectrum of crystalline p-diiodobenzene and interpreted their findings as evidence of strong vibronic coupling between molecular states. Within the band-theory model of excess charge transport this implies a wide conduction band in comparison to other molecular crystals and hence a relatively long mean-free path and high drift mobility of the excess charge. In light of these implications we have undertaken a preliminary study of p-diiodobenzene photoconductivity primarily to measure the drift mobilities. Such data are particularly important at this time because of the uncertain state of charge transport theory in molecular crystals as discussed recently by Glaeser and Berry.2 Our study has indeed revealed relatively high drift mobilities. In addition we have found (1) that the action spectrum for charge generation bears no apparent relation to the known portion of the absorption spectrum of crystalline p-diiodobenzene, and (2) a discontinuity in the mobility vs temperature curve which is presently being investigated further.