A new series of aza-BODIPYs (CNÀ X) with significantly redshifted absorbances were designed and synthesized by installation of various electron-donating groups on the para-positions of 3,5-phenyl groups while strong electron-withdrawing groups (nitrile groups) were fixed on the para-positions of 1,7-phenyl moieties. Interestingly, strong electron-donating groups such as N'N-dimethylaniline (CNÀ NMe 2) could provide strong NIR absorption up to 857 nm and weak fluorescence emission up to 967 nm, whereas strong evidence supported heat production via non-radiative decay after excitation. Electrochemical studies revealed that the substituents on the dyes showed strong effects on the oxidation potentials where the oxidation wave of CNÀ NMe 2 occurred at the lowest overpotential, followed by CNÀ OMe, CNÀ Me, CNÀ Br and CNÀ H, respectively. Calculations were also performed to understand the push-pull effect of the substituents on the aza-BODIPY systems. Finally, applications of dyes in NIR cancer cell imaging and the NIR-II photothermal effect were also investigated.