A fluorescent dye with large Stokes shift and high stability: synthesis and application to live cell imaging

A fluorescent dye, 2,5-bis(6-amine-benzoxazol-2-yl) thiophene (BBTA), was synthesized by a two-step reaction from starting material 2,5-bis(benzoxazol-2-yl) thiophene (BBT). BBTA exhibited strong emission and large Stokes shift in solvent, and the largest Stokes shift (Delta lambda = 186 nm or Delta nu = 8572 cm(-1)) was obtained in buffer solution (PBS, pH = 7.2) with 5% (v/v) of polyethylene glycol monomethyl ether (mPEG(550), MW = 550) as additive. Application of BBTA to live cell imaging showed that BBTA was clearly expressed in mitochondria with high contrast. Besides, BBTA showed low cytotoxicity and excellent photo-stability.