Significant Improvement of Solid‐State One‐/Two‐Photon Excited Luminescence in HOFs via Constructing Hydrogen‐Bonded Solvate Model

• Published in: Advanced optical materials 2023-03, Vol.11 (6), p.n/a
• Main Authors: Zhang, Lin, Li, Hongjun, Zheng, He‐Qi, Yang, Yu, Cui, Yuanjing, Yang, Deren, Qian, Guodong
• Format: Article
• Language: English
• Subjects: Chemical compounds; Electrons; Fluorescence; Hydrogen; Hydrogen bonds; hydrogen‐bonded organic frameworks; Materials science; Optical materials; Optical properties; Optics; Organic materials; organic optical materials; Photons; quantum yield; solvent molecules; Solvents; two‐photon response
• ISSN: 2195-1071; 2195-1071
• DOI: 10.1002/adom.202202598

A hydrogen‐bonded solvate (HBS) model is herein proposed to construct hydrogen‐bonded organic frameworks (HOFs), for enhancing the solid‐state one‐/two‐photon excited fluorescence (1/2PEF) of organic fluorophores. Two photonic HOFs (ZJU‐HOF‐25 and ZJU‐HOF‐26) are synthesized by using the same organic fluorophore and the fluorophore in them features similar arrangement. The most obvious structural distinction between the two HOFs is the existence of solvent molecules in the crystal cell of ZJU‐HOF‐25. ZJU‐HOF‐25 is regarded as an ideal HBS material where solvent molecules separate fluorophores apart just like dissolving them. But ZJU‐HOF‐26 contains no solvent molecules and the fluorophores are connected directly via hydrogen bonds among them. A significant quantum yield (η) increase is realized from amorphous fluorophores (η ≈0%) to HBS‐based ZJU‐HOF‐25 (η ≈21.75%), while ZJU‐HOF‐26 displays poor 1PEF (η ≈0%). ZJU‐HOF‐25 also exhibits much stronger 2PEF with the two‐photon action cross section larger than ZJU‐HOF‐26 by almost two orders of magnitude. These phenomena are mainly attributed to that the solvent molecules in ZJU‐HOF‐25 benefit the homogeneous separation and conformation fixation of fluorophores, suppressing the non‐radiative transition. The HBS model thus shows the fantastic validity to improve solid‐state optical properties of organic materials, providing guidance for exploring advanced optical materials. A hydrogen‐bonded solvate (HBS) model is constructed by elaborately designing a photonic hydrogen‐bonded organic framework (HOF). The solvent molecules exist in the crystal cell to support the framework, orderly separating and immobilizing the fluorophores. As a result, the emission intensity, quantum yield and two‐photon responses of this HBS‐based HOF are all significantly enhanced compared to amorphous fluorophores.