Light-Modulated Cationic and Anionic Transport Across Protein Biopolymers

Light is a convenient source of energy and the heart of light-harvesting natural systems and devices. Here, we show light-modulation of both the chemical nature and ionic charge carrier concentration within a protein-based biopolymer that was covalently functionalized with photoacids or photobases. Using steady-state and time-resolved fluorescence, we explore the capability of the biopolymer-tethered photoacids and photobases to undergo excited-state proton transfer and capture (ESPT and ESPC), respectively. Various electrical measurements show that both the photoacid- and photobase-functionalized biopolymers exhibit an impressive increase in ionic conductivity upon light irradiation, which can be modulated by the light intensity. Whereas ESPT-induced cationic protons are the charge carriers for the photoacid-functionalized biopolymer, ESPC-induced water-derived anionic hydroxides are the suggested charge carriers for the photobase-functionalized biopolymer. Our work introduces a versatile toolbox to light?modulate charge carriers in polymers and taking together the attractive environmental nature of our new light-modulated ionic-conductive biopolymers, they can be considered for various photoelectrochemical applications.