Visible Light Induced Electron Transfer and Long-Lived Charge Separated State in Cyanine Dye/Layered Titanate Intercalation Compounds

Visible light induced guest-to-host electron transfer and formation of long-lived charge separated state were demonstrated in cyanine dye/layered titanate intercalation compounds. 1,1′-Diethyl-2,2′-cyanine (dye-1) and 5,5′-dichloro-3,3′,9-triethyl-thiacarbocyanine (dye-2) were intercalated into layered titanates, Cs_xTi _2-x/4□_x/4O₄ (□ = vacancy, x = 0.7) and Na₂Ti₃O₇, by cation exchange reactions with alkylammonium-exchanged forms as the intermediates. The formation of the intercalation compounds was confirmed by XRD, elemental analysis, and visible absorption and fluorescence spectroscopies. The intercalated dyes formed J-aggregates in the interlayer spaces for all the dye/titanate systems. The visible light induced electron transfer was shown by the appearance of ESR signal, which was ascribed to the radical dications of the dyes, and by the quenching of the fluorescence of the dye aggregates. Apparent lifetimes of the charge separated states were estimated from the decay curve of the ESR signal. The charge separated state was most stable in the dye-2/Cs_xTi _2-x/4□_x/4O₄system with the lifetime of 246 min among four tested compounds.