Macrocyclization-induce emission enhancement characteristics of benzothiadiazole-based macrocycles: A theoretical study

Abstract

We present a comprehensive investigation into the molecular structures in the ground state and the first singlet excited state, intramolecular and intermolecular interactions, as well as the emission properties of monomers, dimers and macrocycles using density functional theory and time-dependent density functional theory. Our study aims to unveil the macrocyclization-induce emission enhancement principle for benzothiadiazole-based macrocycles. Compared with the typical π-π stacking of monomers, macrocycles exhibit the tighter stacking arrangement due to the presence of strong intramolecular and intermolecular hydrogen bond interactions and the rigid triangular geometry of macrocycle, which is conducive to the enhancement of emissions efficiency. The calculated oscillator strength of macrocycles in the first excited state is much higher than that of dimers composed of two monomers. Meanwhile, the large transition electric dipole moment is beneficial for enhancing the emission efficiency. Additionally, our study reveals an emission wavelength red-shift for macrocycles after “CH”/N substitution in the acceptor moiety, and the transition mode from LUMO to HOMO can be mainly attributed to intramolecular charge transition characters from acceptor to donor fragments. Our theoretical study might provide valuable insights for the design of innovative luminescent macrocycles with high emission efficiency.