Design, synthesis, and evaluation of azo D-π-A dyes as photothermal agents

Thirteen readily accessible azo D-pi-A dyes, intended for use as photothermal agents, were synthesized using only a few steps. Absorption wavelengths were readily tuned by changing the building blocks, and 6 of these dyes exhibited NIR absorption that would be useful for biomedical applications. Unexpected suppression of an N-C single bond rotation that neighbors the azo bond was observed in the case of 5 dyes. Photothermal conversion efficiency measurements revealed a significant effect of the D moiety in these synthesized azo D-pi-A dyes, but neither the pi moiety nor the A moiety showed an obvious influence. The obtained results offer valuable information for the design of high-performance azo D-pi-A dyes that have utility as photothermal agents.