Diarylamine-Fused Subporphyrins: Proof of Twisted Intramolecular Charge Transfer (TICT) Mechanism

Koki Kise; Yongseok Hong; Norihito Fukui; Daiki Shimizu; Dongho Kim; Atsuhiro Osuka

doi:10.1002/chem.201801576

Diarylamine-Fused Subporphyrins: Proof of Twisted Intramolecular Charge Transfer (TICT) Mechanism

Chemistry. 2018 Jun 12;24(33):8306-8310. doi: 10.1002/chem.201801576. Epub 2018 May 15.

Authors

Koki Kise¹, Yongseok Hong², Norihito Fukui¹, Daiki Shimizu¹, Dongho Kim², Atsuhiro Osuka¹

Affiliations

¹ Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto, 606-8502, Japan.
² Spectroscopy Laboratory of Functional π-Electronic Systems and Department of Chemistry, Yonsei University, 50, Yonsei-ro, Seodaemun-gu, Seoul, 03722, Korea.

PMID: 29667245
DOI: 10.1002/chem.201801576

Abstract

Diarylamine-fused subporphyrins 1 a and 1 b were synthesized from β,β-diiodo-meso-chloro subporphyrin 2 through a one-pot procedure involving nucleophilic aromatic substitution and S_RN 1-type intramolecular fusion reaction as the first example of meso-nitrogen-embedded subporphyrin. While non-fused counterparts 3 b and 4 b display effective fluorescence quenching due to twisted intramolecular charge transfer (TICT) in CH₂ Cl₂ at room temperature, 1 b emits fluorescence with Φ_F =0.18 under the same conditions, because conformational twisting is not allowed due to the fused structure. In addition, the oxidative titration with tris(4-bromophenyl)ammoniumyl hexachloroantimonate gave cation radical 7 for 1 a and cation radical and dication for 1 b. Actually, cation radical 7 was isolated through separation over silica gel column but was found to slowly decompose in concentrated solutions.

Keywords: TICT; cation radicals; embedded heteroatoms; fluorescence; subporphyrin.