An unexpected non-conjugated AIEgen with a discrete dimer for pure intermolecular through-space charge transfer emission

Manipulation of the charge transfer in donor-acceptor-type molecules is essential for the design of controllable aggregate luminescent materials. Apart from the traditional through-bond charge transfer (TBCT) systems which suffer from complicated structural design, poor tunability and low quantum efficiency, through-space charge transfer (TSCT) has been proved as an alternative yet facile strategy in tuning photophysical processes. In this work, by simply changing nucleophilic reaction bases, a traditional conjugated acrylonitrile AP1 and an unexpected non-conjugated AP2 with a carboxamide-functionalized oxirane linker could be obtained. The long-range π-π stacking in conjugated AP1 results in mixed intramolecular TBCT plus intermolecular TSCT emission. However, facilitated by the steric hindrance effect of the big oxirane connector and the unique discrete dimer packing, non-conjugated AP2 exhibits pure and efficient intermolecular TSCT emission in both aggregate and crystalline states. The flexibility of the non-conjugated character further leads to better reversible stimuli-responsiveness to mechanical force for AP2 than for the rigid AP1 . By using different bases, a conjugated acrylonitrile with mixed intramolecular TBCT plus intermolecular TSCT emission and an oxirane-based non-conjugated dye with pure intermolecular TSCT emission in aggregate and crystalline states were realized.