Preparation, single-crystal structure and room-temperature phosphorescence of a covalent organic polymer containing...

Room-temperature phosphorescent (RTP) single crystals of covalent organic polymers (COPs) are rarely reported due to the huge challenge in preparing single crystals from solutions as well as the difficulty in realizing RTP in metal-free organic molecules. Compared to other main group elements, tellurium is rarely successfully introduced into functional single-crystal COPs. Herein, we prepared colorless single crystals of a COP (CityU-21) through a reaction between tellurinyldibenzene and [1,1'-biphenyl]-4,4'-diyl-bis(phosphonic acid). Single crystal X-ray diffraction (SCXRD) analysis indicates that CityU-21 is a one-dimensional organic polymer through the covalent connection (Te-O-P bonds) between Te(Ph)₂ moieties and [HO₃P-Ph-Ph-PO₃H] units. Due to the existence of one unreacted OH group in each phosphonic acid unit, multiple hydrogen-bonding interactions can be formed between adjacent polymer chains, which stabilizes the structure and promotes CityU-21 to form a pseudo-two-dimensional framework. Benefiting from the integrated effect of aromatic P[double bond, length as m-dash]O parts, the heavy atoms (tellurium), and multiple hydrogen bonds, single crystals of CityU-21 display RTP behavior with a lifetime of 179 ms @ 540 nm and 158 ms @ 565 nm, a photoluminescence quantum yield of 84.69% and an afterglow time of 1.2 s. Moreover, CityU-21 can maintain its crystallinity and RTP character with an afterglow time of up to 0.8 s after immersion in different solvents for 60 hours, which can address the issue that most single crystals of RTP small molecules lose their crystallinity and RTP properties after solvent treatment.