Thermally Activated Delayed Fluorescence Under Arrest: The Role of Hydrogen Bonding Environments

Thermally activated delayed fluorescence (TADF) is a promising innovation in display technology where the nonemissive triplet excitons can be thermally converted back into emissive singlet excitons through reverse intersystem crossing. Organic TADF emitters often feature donor–acceptor (D–A) architectures, where molecular conformation critically influences emission dynamics and efficiency. Introducing intramolecular hydrogen-bonding between D and A moieties is an emerging strategy to rigidify the structure and improving TADF emission. However the influence of environmental factors on such hydrogen-bonding interactions remains unclear. Here we investigate the impact of hydrogen-bonding medium on TADF emission using steady-state and time-resolved emission spectroscopy. Protic solvents quench TADF emission significantly, correlating with reduced prompt emission lifetimes, while delayed lifetimes remain unchanged. Ultrafast studies reveal a picosecond D-to-A intramolecular charge transfer event that slows in viscous media indicating a D-A torsional relaxation. The relaxation time further slows in protic environment highlighting the role of solvent-chromophore hydrogen-bonding interaction resulting in unfavourable excited state D-A conformations and diminished emission. These findings underscore the importance of microenvironment control in designing efficient TADF emitters for display applications and photocatalysis.