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Synthesis of Anthraquinone Mono- and Diboron Complexes with Near-Infrared Panchromatic Absorption
Yasuhiro Kubota1, Ayumi Ogasawara1, Shota Mizuno1
1Department of Chemistry and Biomolecular Science, Faculty of Engineering, Gifu University, 1-1 Yanagido, Gifu, 501-1193, Japan.
None:
Anthraquinone monoboron complexes 3 and 4, possessing a donor-acceptor (D-A) structure, and diboron complexes 7 and 8, featuring a donor-acceptor-donor (D-A-D) structure, were readily synthesized in two steps from commercially available reagents. These boron complexes adopt a β-iminoenolate structure and their absorption properties are markedly affected by the type of the substituent groups. The unsubstituted monoboron complex 3 (fwhm = 3,950 cm-1) and diboron complex 7 (fwhm = 2,510 cm-1) exhibited sharp UV-Vis-NIR absorption spectra, which can be attributed to increased molecular rigidity induced by boron coordination. In contrast, the dimethylamino-substituted monoboron complex 4 (fwhm = 7,580 cm-1) and diboron complex 8 (fwhm = 8,770 cm-1) showed broad absorption bands due to the enhanced intramolecular charge-transfer (ICT) character. Dimethylamino-substituted monoboron complex 4 and diboron complex 8 exhibited panchromatic absorption ranging from 400 nm to 1,000 nm and 400 nm to 1,250 nm, respectively. The panchromatic absorption of the dimethylamino-substituted boron complexes 4 and 8 is attributed not only to the enhanced ICT character but also to the combination of multiple transitions.
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