Triplet Excitons in Carbon Nitride Materials: From Melem Monomers to Extended Polymers

Owing to their earth-abundant constituents and tunable electronic structure, Carbon Nitride (CN) materials have emerged as a versatile class of photocatalytic systems. Their photocatalytic activity is linked to a complex excited-state landscape, where the role of triplet excitons remains under debate. In this work, we use time-resolved electron paramagnetic resonance (TR-EPR) spectroscopy to directly probe the spatial extent of triplet excitons as a function of the degree of thermal polymerization. We find that fully polymerized CN frameworks sustain strongly delocalized triplet excitons, in contrast to the localized states observed in incompletely condensed structures containing molecular or oligomeric units. These results establish a clear connection between network polymerization and exciton delocalization, providing mechanistic insight into the photophysical processes that govern charge separation and reactivity in CN-based photocatalysts.