Fjord-Type AIEgens Based on Inherent Through-Space Conjugation

Through-space conjugation (TSC) is a noncovalently electronic interaction that is emerging as a potential complement to through-bond conjugation (TBC)- based strategies for constructing luminescent materials. However, the design of efficient luminogens based on TSC is currently challenging due to a lack of established structure-property understanding. This is particularly true in the case of luminogens displaying aggregation-induced emission (AIE) effects. In this work, three terphenyl derivatives were prepared, and their photophysical properties were systemically studied. It was found that relative to the corresponding m- and p-linked analogues, the electronic interaction of TBC is weakened while the strength of TSC is commensurately enhanced in the constitutional isomer containing an o-linked fjordtype subunit. Within this set of luminogens, the presence of a fjord-type arrangement promotes a transformation from aggregation-caused quenching to AIE. Further investigations involving congeneric quaterphenyl and pentphenyl isomers support the universality of the fjord-type unit as a framework for synthesizing AIE-active luminogens (AIEgens) with inherent TSC. This work not only provides a novel set of AIEgens but also establishes the utility of TSC in controlling the photophysical properties of nonconventional and twisted luminogens.