ESTIMATION OF EXCITON SIZES IN SQUARAINE MONOLAYERS BY INTRALAYER PHOTOINDUCED ELECTRON-TRANSFER

The effect of intralayer electron acceptor and donor on the photocurrent generation of monolayer modified SnO2 electrodes of DSSQ (4-(distearylamino)phenyl-4'-(dimethylamino)phenylsquaraine) has been investigated in solution photoelectrochemical experiments. While intralayer electron accepters, such as C(14)MV(2+) (1-methyl-1'-tetradecyl-4,4'-bipyridinium dichloride), are shown to promote cathodic photocurrent generations under both ambient and deaerated conditions, C(18)PDA (N,N-dioctadecyl-p-phenylenediamine), an intralayer donor, is found to quench the cathodic photocurrent under ambient condition and make the photocurrent anodic when the electrolyte solution is deaerated with N-2 From the effects of the concentration of the donor/ acceptor on the photocurrent generation process, and the assumption that the squaraine chromophores are in a ''card pack'' (translation or glide layer packing) arrangement in the monolayers, the size of the exciton in the aggregated monolayer is estimated to consist of similar to 25 DSSQ molecules, Evidence is provided that aggregates with higher quantum efficiency of photocurrent generation can be obtained when the monolayer is prepared at subphase temperatures higher than 55 degrees C. The increase in quantum efficiency is discussed in terms of the increase in the exciton diffusion length.