Cyclic conjugated molecules have garnered theoretical and synthetic interest for decades as unique continuous pi-electron systems with radial orientation of p orbitals. Our understanding of cyclic conjugation remains far behind the much more studied linear pi electron delocalization, especially in exotic systems maintaining both cyclic and linear conjugation pathways. In this contribution, we describe the synthesis and electronic properties of small-molecule and polymeric cycloparaphenylenes (CPPs) as part of extended linearly pi-conjugated frameworks. Arylene-ethynylene linkers were installed on different positions of the CPP nanohoop, for example in “linear conjugation” with two alkynes on the same phenyl ring, or in “disjoint conjugation” as separated by three phenyl units on either side. We demonstrate new electronic states from this radial/linear mixing in both small oligomers and pi extended polymers. Quantum chemical calculations reveal these electronic processes to arise from multiple operative radial/linear conjugation pathways. We show how the disjointed substitution pattern necessarily forces delocalization through and around the CPP radial structure. Our findings are supported by extensive model studies to decouple the influences of the linear and radial contributions. These results affirm the unique nature of hybrid radial and linear pi electron delocalization operative in these new conjugation pathways.

Crafting linear and radial conjugation through pi-conjugated polymers

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ACS Fall 2022

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