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.

Signal Transduction Allows Temporal Control of the Potential of a Concentration Cell Driven by the Decarboxylation of an Activated Carboxylic Acid

“…Remarkably, the device we obtained could be interfaced with electric circuits, thus coupling their operation to the working cycle of an activated carboxylic acid with no intervention from the operator besides the addition of 1 in a fire‐and‐forget fashion. To the best of our knowledge, this work reports the first example of the transduction of a transient chemical signal due to a transient chemical stimulus [28] into a transient voltage signal for the operation of a system that is not by itself sensitive to acids and bases. While the use of activated carboxylic acids was previously restricted solely to pH‐sensitive systems, here, by transducing the pH cycle into a voltage cycle, we provided a convenient method for applying the well‐known chemistry of decarboxylative fuels to systems that are otherwise unaffected by pH changes.…”

An Indolin‐3‐imine Photobase and pH Sensitive Fluorophore

“…Such photoacids/photobases, have attracted attention due to the prospect of exploiting their properties in various valuable applications [9] . These include photocurrent generation, [10] light‐mediated polymerization [11] and enantioselective protonation of silyl enol ethers, which allows for stereospecific synthesis of α‐substituted carbonyls [12] …”

Light-Triggered Reversible Change in the Electronic Structure of MoO3 Nanosheets via an Excited-State Proton Transfer Mechanism

“…For the common 8-hydroxypyrene-1,3,6-trisulfonate (HPTS) photoacid that we used in this study, the ground- and excited-state p K a values are 7.4 and 0.4, respectively. Importantly, the proton dissociation of such photoacids is reversible, and upon returning to the ground state, the deprotonated species (RO – ) is reprotonated. − The reversible ESPT from a photoacid to a nearby proton acceptor can be utilized to light-trigger various processes that are dependent on protonation, − which are conceptually acid–base reactions. Here, we show that MoO 3 nanosheets can serve as proton acceptors to a photoacid, resulting in a light-triggered change in the redox state of MoO 3 nanosheets to nonstoichiometric MoO 3– x nanosheets and reversible oxidation in the dark.…”