Dye sensitization has been widely studied in electrochemical photovoltaic cells. More recently, a similar concept has been explored within the context of photoelectrochemical (PEC) water splitting, with a particular facus on TiO2 photoelectrodes. Despite the prevalence of organometallic complexes featuring expensive metals (Ru, Ir) in current dye and molecular catalyst research, efforts should be directed towards more abundant metals and purely organic photoactive compounds. One of the most efficient molecular structures in rr-conjugated building blocks organic to boost metal-free intramolecular dyes combines charge donar transfer (D), and acceptor electron (A), transport and to TiO2. In this communication, the water-splitting performance of TiO2 electrodes TiO2. sensitized with a series of such dye molecules (Table 1 ), including their possible combination with carbon nanomaterials, is summarized and analyzed. Electronic HOMO and HUMO levels, as well as reduction potentials of the dye molecules, reveal favorable thermodynamicreveal conditions, whereas their limited stability under water oxidation conditions seems to be related to purely kinetic effects. Tackling this challenge effects. remains crucial yetfar achieving future advances toward an artificial photosynthesis.

Financial support from MCIN/AEl/10.13039/501100011033, MICIU/AEI/10.13039/501100011033 and "ERDF A Way of making Europe" under project grant PID2022-139671O8-I00 and CEX2023-001286-S, as well as from the Gobierno de Aragón (DGA, T03_23R and E47-23R) and Universidad de Zaragoza (UZ2023-CIE-01).

Work presented at III Workshop on Materials far Photocatalysis, Energy and Clean Environment (IIIWMPECE), ICMS -Sevilla, (Spain), February 20-21, 2025.

With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2023-001286-S).

Peer reviewed