Fig. 4: HO‑PBA trimer and its structural characterization.
From: Water-stable boroxine structure with dynamic covalent bonds
a ESI-Q-TOF mass spectrum of HO‑PBA dimer in a methanol–water (5:1, v/v) solution, acquired in a negative mode. HO‑PBA trimer is donated by T. b Photos of the HO‑PBA trimer solution after addition of Br2 (circle) and FeCl3 (triangle). c UV–Raman spectra of the solid TPB (black) and PBA (red) sample, TPB (purple) and PBA (blue) in an ACN–water (1:2, v/v) solution, and an ACN–water (1:2, v/v) mixture (cyan). d UV–Raman spectra of the solid HO‑PBA dimer sample (black), HO‑PBA dimer in a dry ACN solution (red) and HO‑PBA trimer in an ACN–water (1:2, v/v) solution (blue). e Optimized geometry of HO‑PBA trimer, calculated by Gaussian at the B3LYP/6-31 G* level. The dashed dark blue lines represent intramolecular O–H…O hydrogen bonds. D(w2–w1) represents the dihedral angle between w1 and w2. f Comparison of the calculated and experimental fluorescent spectra of HO‑PBA trimer in water. g Frontier molecular orbitals of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of HO‑PBA trimer in the excited state. h Relative fluorescence intensity at 368 nm of HO‑PBA trimer (F/Fmax) as a function of pH value. i ESI-Q-TOF mass spectrum of HO‑PBA trimer in methanol–H218O (5:1, v/v) solution, acquired in a negative mode.
