The H-aggregates of cresyl violet dye which are formed on the negatively charged SiO2 and SnO2 nanocrystallites, exhibit relatively short-lived excitonic singlet state with a lifetime of about 35 ps. The difference absorption maximum (lambda(max)=470 nm) is blue shifted compared to the corresponding singlet excited state of monomer (lambda(max)=515 nm). Time-resolved transient absorption measurements show that these dye aggregates are capable of injecting electrons from the triplet excited state into SnO2 nanocrystallites. The rate constant for heterogeneous electron transfer as measured from the formation of cation radical and electron trapping in SnO2 nanocrystallites was 2.0X10(8) s(-1).