Substituent-Driven Dual Emission and Thermoresponsive Phosphorescence from <i>N</i>-Borylated Carbazoles

Recently, aminoboranes have emerged as a new class of room-temperature phosphorescence materials, attracting significant attention due to their unique photophysical properties, particularly their exceptional triplet harvesting capacity, which stems from the mixed symmetry of their singlet and triplet states. Here, we report a series of N-borylated carbazoles (1Cbz–4Cbz), exhibiting simultaneous delayed fluorescence (DF) and room-temperature phosphorescence (RTP). The relative contributions of these emissions are altered by modifying the substituents on the carbazole donor and diarylborane acceptor units. Interestingly, these molecules exhibit thermoresponsive phosphorescence, shifting from greenish yellow (450–520 nm) at low temperatures (LT) to orange-red (530 −640 nm) at room temperature (RT). Detailed photoluminescence investigations and quantum chemical computations reveal that LT phosphorescence originates from triplet states of isolated molecules, whereas molecular assemblies in the condensed phases show the red-shifted RT phosphorescence.