Tuning Multicolor Emission from a Single Fluorophore via Controlled Radical Polymerization-Mediated Charge Transfer

Tuning emission color of molecular fluorophores is of fundamental interest as it directly reflects the manipulation of excited states at the quantum-mechanical level. Despite recent progress in molecular design and engineering on single fluorophores, a systematic methodology to obtain multicolor emission in aggregated or solid states, which gives rise to practical implications in different fields, remains scarce. This is due to the complex interplay between the charge-transfer (CT) and singlet excitons. In this study, we present a general strategy to tune the emission color of a single-fluorophore aggregate by controlled radical polymerization-mediated charge transfer. Using a library of well-defined styrenic donor (D) polymers grown from an acceptor (A) fluorophore by atom transfer radical polymerization (ATRP), we found that the solid-state emission color can be fine-tuned by varying three molecular parameters: (i) the monomer substituent, (ii) the end-groups of the polymer, and (iii) the polymer chain length. Experimental and theoretical investigations reveal that the color tunability originates from the structurally dependent through-space charge transfer (TSCT) process that regulates CT energy. We further demonstrate that the polymer systems can be processed into thin films enabling versatile photolithography.