Unraveling the effect of topological structures of B/N-doped conjugated macrocycles on spectral properties: A computational study.
Guo Wen-Yu WY, Zeng Yi Y, Xu Yu-Meng YM, Chen Pang-Kuan PK et al.
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.