Phosphorescence Lighting Aggregation Architectures in Alkyl‐Engineered Branched Luminogens

Branched luminogens can create diverse aggregation microenvironments that critically govern their photophysical properties; however, their inherent conformational flexibility often renders subtle microstructural changes elusive to conventional characterization. Here, we show that tailoring alkyl-chain topology renders room-temperature phosphorescence (RTP) as a sensitive reporter of these microenvironments. Upon thermal annealing, photoinduction, or vacuum deoxygenation, the afterglow varies systematically with chain length and odd-even parity, confirming that RTP monitors cavity-restricted environments and aggregate structures. Theoretical calculations further reveal that longer chains strengthen intermolecular interactions, whereas odd-even parity dictates packing modes and cavity distributions; together, these factors control oxygen diffusion and triplet deactivation. Thus, this work establishes the relation among chain topology, aggregation architecture, and RTP property, providing an efficient approach to decode subtle evolutions in branched aggregates.