High - Potential Porphyrins Supported on SnO 2 and TiO 2 Surfaces for 2 Photoelectrochemical Applications

8 ABSTRACT: We report CF3-substituted porphyrins and 9 evaluate their use as photosensitizers in water-splitting dye10 sensitized photoelectrochemical cells (WS-DSPECs) by 11 characterizing interfacial electron transfer on metal oxide 12 surfaces. By using (CF3)2C6H3 instead of C6F5 substituents at 13 the meso positions, we obtain the desired high potentials while 14 avoiding the sensitivity of C6F5 substituents to nucleophilic 15 substitution, a process that limits the types of synthetic 16 reactions that can be used. Both the number of CF3 groups 17 and the central metal tune the ground and excited-state 18 potentials. A pair of porphyrins bearing carboxylic acids as 19 anchoring groups were deposited on SnO2 and TiO2 surfaces, 20 and the interfacial charge-injection and charge-recombination kinetics were characterized by using a combination of 21 computational modeling, terahertz measurements, and transient absorption spectroscopy. We find that both free-base and 22 metalated porphyrins inject into SnO2 and that recombination is slower for the latter case. These findings demonstrate that 23 (CF3)2C6H3-substituted porphyrins are promising photosensitizers for use in WS-DSPECs.