Fast and ultrafast charge transfer dynamics in organic dye sensitizers anchored on TiO 2 for photoelectrochemical cells

Three organic conjugated donor–acceptor dyes with hydrophobic side chains were studied as potential photosensitizers for dye-sensitized photoelectrochemical cells (DS-PECs). The dyes were anchored on TiO2 electrodes and investigated using steady-state and femtosecond transient absorption spectroscopies. Optical studies revealed intramolecular charge transfer (ICT) as the dominant excitation pathway, with AD418 showing single-state emission and BTD-DTP1/TTZ5 displaying dual ICT emission. On TiO2, ultrafast electron injection (1–2 ps) leads to long-lived mono-cationic species, indicating effective charge separation.