Hole mobility in microcrystalline chlorophyll a

The measurements of hole mobility in microcrystalline chlorophyll a (Chl a) as a function of temperature and field have been carried out. The results are described in terms of disorder formalism of charge transport put forwar d by Bassler and co-workers. Noteworthy feature of the study is the negativ e field dependence of the mobility at room temperature. This is explained o n the basis of the presence of large positional disorder parameter, Sigma, compared to the energetic disorder, sigma, in microcrystalline Ch1 a. Their respective values are approximate to 4 and 77 meV The intercalation of a w ater molecule that holds the two Chi a molecules together to form microcrys talline Ch1 a is a possible responsible for the increased hopping site dist ances that leads to larger Sigma and, thus, to the negative field dependenc e of the mobility.