Photocurrent Generation and Polarity Switching in Electrochemical Cells through Light‐induced Excited State Proton Transfer of Photoacids and Photobases**

Abstract

Light is a common source of energy in sustainable technologies for photocurrent generation. To date, in such light‐harvesting applications, the excited electrons generate the photocurrent. Here, we introduce a new mechanism for photocurrent generation that is based on excited state proton transfer (ESPT) of photoacids and photobases that can donate or accept a proton, respectively, but only after excitation. We show that the formed ions following ESPT can either serve as electron donors or acceptors with the electrodes, or modify the kinetics of mass transport across the diffuse layer, both resulting in photocurrent generation. We further show that control of the current polarity is obtained by switching the irradiation between the photoacid and the photobase. Our study represents a new approach in photoelectrochemistry by introducing ESPT processes, which can be further utilized in light‐responsive energy production or energy storage.

A dual photobase system for directing the pathway of pH-sensitive chemical reactions with light

“…[28][29][30][31] Brønsted photobases have been used to control chemical reactions in various functional systems, including catalysis photoactivation, light-induced droplet self-propulsion, photocurrent generation, dynamic selfassembly, and light-modulated ionic transport. [32][33][34][35] The use of MGCB in functional systems involves light-driven DNA conformational switches, photoresponsive hydrogels, dynamic selfassembly, and photoresponsive photonic crystals. [36][37][38][39] In this work, we control the reaction pathways of the organic dye Alizarin Red S (ARS) using the unique interaction between two photobases of Arrhenius and Brønsted types, having different excitation wavelengths and photoreaction timescales.…”

Manipulating the electronic properties and structure of MoO3 nanosheets with light via an excited-state proton transfer mechanism

“…Importantly, the proton dissociation of such photoacids is reversible, and upon returning to the ground state, the deprotonated species (RO -) is re-protonated. [14][15][16] The reversible ESPT from a photoacid to a nearby proton acceptor can be utilized to light-trigger various processes that are dependent on protonation, [17][18][19][20][21][22] which are conceptually acid-base reactions. Here, we show that MoO3 nanosheets can serve as proton acceptors to a photoacid, resulting in a light-triggered change in the redox state of MoO3 nanosheets to nonstoichiometric MoO3-x nanosheets and reversible oxidation in the dark.…”