Dithienoarsole: A Novel Class of Heteroradialenes

• Published in: European journal of organic chemistry 2020-07, Vol.2020 (26), p.3965-3970
• Main Authors: Urushizaki, Aya, Yumura, Takashi, Kitagawa, Yuichi, Hasegawa, Yasuchika, Imoto, Hiroaki, Naka, Kensuke
• Format: Article
• Language: English
• Subjects: Aromaticity; Crystallography; Density functional theory; Dimerization; Fluorescence; Oligomerization; Phosphorescence; Structural analysis; Time dependence
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.202000442

[5]Radialene is known as an unstable cyclic hydrocarbon with a cross‐conjugated system. Incorporation of heteroatoms into [5]radialene skeleton is an effective strategy for stabilization. Herein we synthesized dithieno[3,4‐b:3',4'‐d]arsole (1) as a novel class of hetero[5]radialenes since trivalent arsenic atom is much more stable than phosphorus one, which was used for hetero[5]radialene but unstable in air. The characteristic nature of the arsa[5]radialene was experimentally and computationally studied by comparing with the isomer, dithieno[3,2‐b:2',3'‐d]arsole (2). Structural analysis by X‐ray crystallography and computational evaluation of aromaticity revealed the radialene character of 1. Interestingly, 1 showed phosphorescence though only fluorescence was observed for 2. Time‐dependent density functional theory (TD‐DFT) calculations implied that intersystem crossing could readily occur upon excitation for 1. Furthermore, it was computationally elucidated that dimerization and/or oligomerization via Diels‐Alder reaction, which convert [5]radialene, were circumvented to offer stability for 1.