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

The effect of intralayer electron acceptor and donor on the photocurre nt generation of monolayer modified SnO2 electrodes of DSSQ rylamino)p henyl-4'-(dimethylamino)phenylsquaraine) has been investigated in solu tion photoelectrochemical experiments. While intralayer electron accep ters, such as C(14)MV(2+) (1-methyl-1'-tetradecyl-4,4'-bipyridinium di chloride), are shown to promote cathodic photocurrent generations unde r both ambient and deaerated conditions, C(18)PDA (N,N-dioctadecyl-p-p henylenediamine), 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 genera tion process, and the assumption that the squaraine chromophores are i n 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 pro vided that aggregates with higher quantum efficiency of photocurrent g eneration can be obtained when the monolayer is prepared at subphase t emperatures higher than 55 degrees C. The increase in quantum efficien cy is discussed in terms of the increase in the exciton diffusion leng th.