The synthesis, crystal structure and room-temperature phosphorescence (RTP) of a 2D metal-free inorganic covalent framework ((H2en) [B5O8(OH)], named as CityU-12, and en represents for ethylenediamine) are reported. The precise structure information of CityU-12 has been disclosed through both single-crystal X-ray diffraction (SCXRD) analysis and low-dose high-resolution transmission electron microscopy (LD-HRTEM) study. The SCXRD results show that CityU-12 composes of 2D anionic B─O-based covalent inorganic frameworks with protonated ethylenediamine locating in the pore sites of 2D B─O layers while LD-HRTEM suggests that CityU-12 has an interplanar distance of 0.60 nm for (00 ) crystal plane and 0.60 nm for (10 ) crystal plane. The optical studies show that CityU-12 is an excellent nonconventional RTP material with the emission peak at 530 nm and a lifetime of 1.5 s. The quantum yield is 84.6% and the afterglow time is as long as 2.5 s. This work demonstrates that metal-free B─O frameworks can be promising nonconventional phosphors for RTP.
Keywords: borate; inorganic covalent framework; low‐dose high‐resolution transmission electron microscopy; room‐temperature phosphorescence; single‐crystal structure.
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