“…Proton transfer is among the most abundant and fundamental processes in organic, inorganic, and biological systems − which can occur between molecules and solvents (intermolecular), leading to a change of the protonation state; or within the molecule itself (intramolecular), resulting in the formation of a constitutional (structural) isomer. Excited-state proton transfer (ESPT) and excited-state intramolecular proton transfer (ESIPT) represent functional processes with distinct underlying mechanisms that have powered broad applications from research labs to industrial settings and from biological to energy fields, which include bioimaging and materials advances. , Recently, there have been extensive studies into the potential of ESIPT reactions from optoelectronic devices, fluorescence sensors, organic light-emitting diodes, lasers, and optical data storages to displays, among others. ,− Many of the molecules possessing ESPT or ESIPT capabilities are naturally occurring, such as the green fluorescent protein (GFP) from Aequorea victoria, , a blue-green pigment xylindein from the fungi Chlorociboria aeruginosa, and a red pigment Draconin red from the fungi Scytalidium cuboideum . The fundamental knowledge and insights obtained that delineate the proton transfer mechanisms in various natural systems have since inspired rational design inquiries and targeted molecular engineering endeavors.…”