A general approach to the design of high-performance near-infrared (NIR) D-π-A type fluorescent dyes

Near infrared (NIR) absorbing and emitting dyes are sought after for their potentials in bioimaging and theranostic applications. They are typically not as stable as dyes absorbing and emitting in the visible spectral range, as the result of a reduced HOMO-LUMO band-gap. Also, they are not as efficient fluorescence emitters due to accelerated internal conversion kinetics. In addition, their large conjugative backbone render them high tendency to form aggregate and low aqueous solubility. In this tutorial, we have described a four-step approach for rational design of organic dyes with an overall high-performance to meet the rigorous requirements of biological applications. Also, some background regarding "NIR" is provided along with some recent breakthroughs of the field.