General Strategy For Tuning The Stokes Shifts Of Near Infrared Cyanine Dyes

We report a significant Stokes shift enhancement in near-infrared fluorescing cyanines as a result of C4 '-substitution with cyclic or acyclic amines. Based on a combined experimental and density functional study, a simple strategy for optimizing the Stokes shift is proposed. By tuning the relative energies of cyanine-like and bis-dipolar conformers, differing in the rotational angle of the amine substituent, it is possible to develop molecules that undergo conformational change upon excitation, resulting in a predictable Stokes shift.