Topologically Engineering of π-Conjugated Macrocycles: Tunable Emissions and Photochemical Reactions

The topology of conjugated macrocycles had significant impacts on their photo-physical and photo-chemical properties. Herein, a series of π-conjugated macrocycles with diverse topology were synthesized via intramolecular McMurry coupling. Their chemical structure and macrocyclic topology were unambiguously confirmed via NMR, MALDI-TOF mass spectra, and scanning tunneling microscopy (STM). Depending on the structural topology and structural rigidity, these macrocyclic luminogens display obviously distinctive emission behavior and photochemical reactions in the solution and in the solid state. Monocyclic MST with lower strain was more susceptible to intramolecular motions, and thus exhibited aggregation-induced emission properties. After UV light irradiation, MST was also vulnerable to undergo photo-cyclization in solution and triplet sensitizer promoted photo-dimerization, and yielded the anti-dimer via triplet excimer on the HOPG surface confirmed by STM investigation. By contrast, highly constrained bis-macrocyclic luminogens DMTPE, featured with high emission quantum yields of 68% both in solution and in the solid state, was relatively inert to photochemical reactions and yield syn-dimer on the surface via singlet excimer involved [2+2] photo-dimerization.