TICT caused quenching in organic semiconductors

A mechanistic understanding of how molecular structure governs photoluminescence quantum yield (PLQY) in non-fullerene acceptors (NFAs) remains elusive, hindering further progress in organic solar cells. Here, we report a comprehensive study of nearly 100 organic semiconductors—primarily NFAs—with emission peaks spanning 550-1000 nm and PLQY values ranging from < 0.01 to > 0.70. We find that the commonly used structural, photophysical, and quantum descriptors fail to account for the observed variations. Instead, we identify the twisted intramolecular charge transfer (TICT) state as the primary quenching pathway. Through a combination of experimental spectroscopy, quantum calculations, and exciton decay dynamics, we show that TICT acts as a dark state on the first excited-state potential energy surface, leading to suppressed PLQY and multi-exponential decay. Crucially, suppressing TICT formation enables substantial enhancements in emission intensity. These results reveal a unifying mechanism underlying luminescence in organic semiconductors, provide a predictive framework for exciton dynamics, and open new avenues for NFA-based technologies beyond photovoltaics. Crucially, this is the first structurally resolved new species yet identified in NFA samples.