Fast and ultrafast charge transfer dynamics in organic dye sensitizers anchored on TiO2 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.