Phenothiazine‐Based D–A′–π–A Photosensitizers With Fluorine Substituent Sensitized Photocatalytic Hydrogen Evolution Under Visible Light

Abstract

A series of four phenothiazine‐based D–A′–π–A organic photosensitizers was designed for photocatalytic hydrogen evolution in conjunction with Pt/TiO 2 . The molecular design strategically extends the conjugation length, thereby effectively broadening the light absorption range. The introduction of fluorine (‐F) and trifluoromethyl (‐CF 3 ) substituents into the π‐bridge serves to stabilize the charge‐separated excited states and suppress charge recombination. Notably, when using benzothiadiazole (BTD) as the auxiliary acceptor, the small atomic radius of fluorine preserves molecular planarity. Consequently, derivatives PBF‐C 8 ‐Py and PBF‐C 12 ‐Py exhibited significantly higher photocurrent densities, indicating superior charge transport capacity. Steady‐state photoluminescence spectra reveal suppressed non‐radiative loss for PBF‐C 8 ‐Py , while its accelerated TRPL decay on TiO 2 and smallest charge‐transfer resistance ( R ct ) in illumination‐dependent EIS collectively demonstrate efficient interfacial charge separation and electron injection into the TiO 2 conduction band. In photocatalytic testing, PBF‐C 8 ‐Py achieved the highest hydrogen evolution yield of 35.62 mmol g −1 over 15.5 h.