Aggregation-induced emission/aggregation-induced emission enhancement (AIE/AIEE) has recently attracted intense research, and a large number of AIE/AIEE luminogens (AIE/AIEEgens) have been constructed for application in diverse scientific fields. The AIE and AIEE effects have similar, but not identical, photophysical behaviors, which are closely related to molecular architectures. However, the current understanding of the inherent differences between AIE and AIEE is still obscure. Herein, a rational design strategy is reported for achieving AIE and AIEE effects by simply incorporating different substituents at the periphery of the same core skeleton. Experimental and theoretical studies on the series of compounds indicated that the restriction of intramolecular twisting motions or/and rotations plays an important role in regard to the corresponding AIE or AIEE behaviors. Moreover, compound 1 a (FW=203, ΦF =80.9 %) was discovered as the lowest molecular weight AIEEgen with a high quantum yield in the solid state despite having no rotatable units. Compound 2 a also exhibited an AIEE effect with the minimum necessary structure (a single ring).
Keywords: aggregation; aggregation-induced emission; fluorescence; nitrogen heterocycles; polycycles.
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