Experimental and computational investigational of unsymmetrical cyanine dyes: Understanding torsionally responsive fluorogenic dyes

A series of fluorinated analogues of the dye thiazole orange that exhibit improved fluorescence quantum yields and photostabilities is described. As per the findings, the computational studies on the dyes revealed that twisting about the monomethine bridge beyond an interplanar angle of 60 degree leads to a dark state that decays nonradiatively to the ground state accounting for the observed fluorogenic behavior.