A Switchable Near‐Infrared‐Absorbing Dye Based on Redox‐Bistable Benzitetraazaporphyrin. Issue 11 (6th February 2023)

• Record Type: Journal Article
• Authors: Yanagi, Shunsuke; Matsumoto, Akihisa; Toriumi, Naoyuki; Tanaka, Yusuke; Miyamoto, Kazunori; Muranaka, Atsuya; Uchiyama, Masanobu
• Is Part Of: Angewandte Chemie international edition. Volume 62:Issue 11(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2023-02-06
• Subjects: Antiaromaticity -- Dyes/Pigments -- Frontier-Orbital Model -- Near-Infrared Light -- Phthalocyanines; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.202218358
• Languages: English
• ISSNs: 1433-7851

Abstract

Abstract: Activatable near‐infrared (NIR) dyes responsive to external stimuli are used in medical and other applications. Here, we describe the design and synthesis of bench‐stable 18π‐ and 20π‐electron benzitetraazaporphyrins (BzTAPs) possessing redox‐switchable NIR properties. X‐Ray, NMR, and UV/Visible‐NIR analyses revealed that 20π‐electron BzTAP 1 exhibits NIR absorption and antiaromaticity with a paratropic ring‐current, while 18π‐electron BzTAP 2 shows weakly aromatic character with NIR inertness. Notably, the NIR‐silent BzTAP 2 was readily converted to the NIR‐active BzTAP 1 in the presence of mild reducing agents such as amine. The intense NIR absorption band of BzTAP 1 is in sharp contrast to the very weak absorption bands of previously reported antiaromatic porphyrinoids. Molecular orbital analysis revealed that symmetry‐lowering perturbation of the 20π‐electron porphyrinoid skeleton enables the HOMO–LUMO transition of 1 to be electric‐dipole‐allowed. BzTAPs are expected to be useful for constructing activatable NIR probes working in reductive environments. Abstract : Bench‐stable, redox‐switchable 18π‐ and 20π‐electron benzitetraazaporphyrins are reported. Whereas the 18π‐electron aromatic form does not show near‐IR absorption, the antiaromatic 20π‐electron form unexpectedly shows intense near‐IR absorption owing to an electric‐dipole‐allowed HOMO–LUMO transition resulting from symmetry‐lowering of the porphyrin skeleton. The redox process is reversible and switching can be repeated multiple times.