An Element-Substituted Cyclobutadiene Exhibiting High-Energy Blue Phosphorescence

Yoshiaki Shoji; Yasuhiro Ikabata; Ivan Ryzhii; Rabia Ayub; Ouissam El Bakouri; Taiga Sato; Qi Wang; Tomoaki Miura; Buddhika S B Karunathilaka; Youichi Tsuchiya; Chihaya Adachi; Henrik Ottosson; Hiromi Nakai; Tadaaki Ikoma; Takanori Fukushima

doi:10.1002/anie.202106490

An Element-Substituted Cyclobutadiene Exhibiting High-Energy Blue Phosphorescence

Angew Chem Int Ed Engl. 2021 Sep 27;60(40):21817-21823. doi: 10.1002/anie.202106490. Epub 2021 Jul 9.

Authors

Yoshiaki Shoji^{1

2}, Yasuhiro Ikabata³, Ivan Ryzhii⁴, Rabia Ayub⁵, Ouissam El Bakouri⁵, Taiga Sato^{1

2}, Qi Wang³, Tomoaki Miura⁴, Buddhika S B Karunathilaka⁶, Youichi Tsuchiya⁶, Chihaya Adachi^{6

7}, Henrik Ottosson⁵, Hiromi Nakai^{3

8}, Tadaaki Ikoma⁴, Takanori Fukushima^{1

2}

Affiliations

¹ Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama, 226-8503, Japan.
² Department of Chemical Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama, 226-8502, Japan.
³ Waseda Research Institute for Science and Engineering, Waseda University, Tokyo, 169-8555, Japan.
⁴ Graduate School of Science and Technology, Niigata University, 2-8050 Ikarashi, Nishi-ku, Niigata, 950-2181, Japan.
⁵ Department of Chemistry-Ångström Laboratory, Uppsala University, 75120, Uppsala, Sweden.
⁶ Center for Organic Photonics and Electronics Research (OPERA), Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, 819-0395, Japan.
⁷ International Institute for Carbon Neutral Energy Research (WPI-I2CNER), Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, 819-0395, Japan.
⁸ Department of Chemistry and Biochemistry, School of Advanced Science and Engineering, Waseda University, Tokyo, 169-8555, Japan.

PMID: 34097333
DOI: 10.1002/anie.202106490

Abstract

1,3,2,4-Diazadiboretidine, an isoelectronic heteroanalogue of cyclobutadiene, is an interesting chemical species in terms of comparison with the carbon system, whereas its properties have never been investigated experimentally. According to Baird's rule, Hückel antiaromatic cyclobutadiene acquires aromaticity in the lowest triplet state. Here we report experimental and theoretical studies on the ground- and excited-state antiaromaticity/aromaticity as well as the photophysical properties of an isolable 1,3,2,4-diazadiboretidine derivative. The crystal structure of the diazadiboretidine derivative revealed that the B₂ N₂ ring adopts a planar rhombic geometry in the ground state. Yet, theoretical calculations showed that the B₂ N₂ ring turns to a square geometry with a nonaromatic character in the lowest triplet state. Notably, the diazadiboretidine derivative has the lowest singlet and triplet states lying at close energy levels and displays blue phosphorescence.

Keywords: DFT calculations; aromaticity; luminescence; main-group elements; reaction mechanisms.

Abstract

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