Unraveling the effect of topological structures of B/N-doped conjugated macrocycles on spectral properties: A...

Organic conjugated macrocycles have attracted significant attention for their applications in smart luminescent materials, yet precise modulation of their spectral properties remains challenging. In this work, a series of fully B-doped, fully N-doped and hybrid B/N-doped conjugated macrocycles were designed to systematically investigate the relationship between their topological structures and spectral properties. Three topological factors of heteroatom doped macrocycles were incorporated into the molecular design: ring size, number of triarylborane (Ar₃B) and triarylamine (Ar₃N) segments, and π-linker between segments. For macrocycles with phenyl as the π-linker, at a fixed ring size, both absorption (λ _abs) and emission (λ _emi) wavelength exhibit a first increase followed by a decrease as the number of Ar₃N segments increases accompanied by the decrease of Ar₃B segments. For each size of macrocycles, the reddest λ _emi usually contains a balanced ratio of Ar₃B and Ar₃N segments, with at least two Ar₃B and Ar₃N segments. Regardless of the ring size of macrocycles, the ratio of Ar₃B to Ar₃N segments plays a crucial role in tuning the spectral properties. A more balanced ratio enhances both electron-donating and electron-accepting abilities, thereby strengthening the intramolecular charge transfer effect and leading to a more redshifted emission spectra. A similar trend of λ _emi that first red-shift then blue-shift was also observed for macrocycles with fluorene or biphenyl as π-linkers. Notably, at a given ring size and relative number of Ar₃N and Ar₃B, phenyl-linked macrocycles exhibit a more pronounced red-shift than those with fluorene or biphenyl linkers, and fluorene-linked systems show slightly red-shifted spectra relative to biphenyl-linked analogs. These spectral trends are well explained by the electronic properties of the fundamental building blocks. This work provides important theoretical guidance for the development of smart luminescent materials based on conjugated macrocycles.