Molecular Crystals and Liquid Crystals, Vol.635, No.1, 158-166, 2016
The excited-state intramolecular proton transfer fluorescence of HBT derivative induced by solvent polarity
In this contribution, a dye (THBT) with 2,5-dimethylthiophene substituted to 2-(2-hydroxyphenyl)benzothiazole was synthesized and characterized by NMR and mass spectroscopic techniques. Its emission behavior in various solvents was investigated and obvious negative solvatochromism was observed. The emission maximum of THBT varied from deep blue (425nm) in DMSO to orange (550nm) in chloroform. It is also highly emissive in polycarbonate film and solid powder with the emission peaks 546 and 554nm, respectively. The ESIPT effect, together with the relaxation of free rotation of thiophene in the excited states, shifted the solid emission 34nm toward longer wavelength furtherly, with respect the 520nm (green) emission of HBT. Quantum calculation of frontier molecular orbitals uncovers the underlying mechanism of negative solvatochromism.