[Molecular Technologies to Utilize Light Energy for Chemical/pharmaceutical Research].

Organic molecules can absorb light energy to form excited states, from which various photophysical and photochemical processes such as heat, emission, and chemical reactions occur during deactivation to ground states. Therefore, it is highly important to control molecular properties in the excited states in many scientific fields including pharmaceutical sciences. Especially, the author has focused on the development of molecular technologies to utilize near-IR light, showing deep tissue penetration favorable for biomedical applications. The author has designed and synthesized 18π-electron tautomeric hydroxybenziphthalocyanines as functional near-IR-light-absorbing compounds with tunable aromaticity. Their near-IR absorption can be controlled by external stimuli such as chemical modifications and solvent effects. Additionally, the benziphthalocyanines were utilized for activatable near-IR photoacoustic imaging probes owing to their nonradiative thermal deactivation processes. The author also succeeded in developing a redox-switchable near-IR dye called benzitetraazaporphyrin. This molecule exhibits strong near-IR absorption in the 20π-electron antiaromatic reduced structure, while the 18π-electron oxidized structure is near-IR silent. The benzitetraazaporphyrin would be useful as near-IR probes working in reductive environments such as cancer cells.