Synthesis and characterization of novel fluorescent BOPIM dyes with large Stokes shift

Synthesis, crystal structures, and photophysical properties of dibromo-2-(2′-pyridyl)imidazole and its corresponding boron–fluorine complex

“…This quite large Stokes shift compared to typical BODIPY dyes (normally 15-30 nm) is possibly due to the CT transition from the electron-donating system to the electron-accepting boron [42]. Compared to the BF 2 chelate with Br substituted by H, the existence of two bromines greatly enlarges the Stokes shift, since BF 2 chelate with no Br only shows Stokes shift of 28 nm [38]. This indicates that p-conjugation between Br and the aromatic rings increases electronic density of the system, facilitating the CT transition.…”

“…Compound L1 2-(2 0 -pyridyl)-4,5-dibromoimidazole was obtained by treating 2-(2 0 -pyridyl)imidazole with bromine according to reported procedure [38,40], as shown in scheme 1. This compound has been characterized by 1 H NMR, 13 C NMR, HRMS, and X-ray single crystal diffraction.…”

“…This compound has been characterized by 1 H NMR, 13 C NMR, HRMS, and X-ray single crystal diffraction. After treatment with BF 3 Á Et 2 O, the corresponding boron chelate 1 can be obtained as a yellow solid in 38% yield after purification by column chromatography [38]. These compounds have been fully characterized by 1 H NMR, 13 C NMR, 19 F NMR, HRMS, and X-ray single crystal diffraction.…”

“…However, the formation of intermolecular hydrogen bond and a halogen bond in crystals makes it emit visibly enhanced fluorescence in crystals. The corresponding boron-fluorine complex, 1, was prepared by treatment of L1 with BF 3 Á Et 2 O under basic condition, as we reported previously [38]. BF 2 chelate is a highly fluorescent chromophore, showing intense fluorescence in solution.…”

A new pH fluorescent molecular switch by modulation of twisted intramolecularcharge transfer with protonation

“…[5,6] Boron 2-(2′-pyridyl) imidazole complex (BOPIM) derivatives, synthesized in our research group, is one class of these samples, which emit intense fluorescence both in solutions and also in solid state with large Stokes shift. [7][8][9][10] Since Lippert studied the intramolecular charge transfer (ICT) process of DMABN, [11] several experimental and theoretical investigations postulate that its emission results from the twisted ICT state of the dialkylamino group. [12][13][14][15] It is also found that ICT process can be mediated by acid or base, due to the protonation or deprotonation.…”