Synthesis, structural analysis, and properties of highly twisted alkenes 13,13’-bis(dibenzo[a,i]fluorenylidene) and its derivatives

• Published in: Nature communications Vol. 14; no. 1; pp. 5248 - 10
• Main Authors: Kang, Hao-Wen, Liu, Yu-Chiao, Shao, Wei-Kai, Wei, Yu-Chen, Hsieh, Chi-Tien, Chen, Bo-Han, Lu, Chih-Hsuan, Yang, Shang-Da, Cheng, Mu-Jeng, Chou, Pi-Tai, Chiang, Ming-Hsi, Wu, Yao-Ting
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 28.08.2023; Nature Publishing Group; Nature Portfolio
• Subjects: 119/118; 140/131; 639/638/298/923/3931; 639/638/403/933; 639/638/440/94; Alkenes; Aromatic compounds; Chemical bonds; Chemistry; Crystallography; Energy gap; Ground state; Humanities and Social Sciences; Molecular orbitals; multidisciplinary; Photoabsorption; Rotation; Science; Science (multidisciplinary); Structural analysis; Synthesis; X-ray crystallography
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-023-40990-8

The rotation of a C = C bond in an alkene can be efficiently accelerated by creating the high-strain ground state and stabilizing the transition state of the process. Herein, the synthesis, structures, and properties of several highly twisted alkenes are comprehensively explored. A facile and practical synthetic approach to target molecules is developed. The twist angles and lengths of the central C = C bonds in these molecules are 36–58° and 1.40–1.43 Å, respectively, and confirmed by X-ray crystallography and DFT calculations. A quasi-planar molecular half with the π-extended substituents delivers a shallow rotational barrier (down to 2.35 kcal/mol), indicating that the rotation of the C = C bond is as facile as that of the aryl-aryl bond in 2-flourobiphenyl. Other versatile and unique properties of the studied compounds include a broad photoabsorption range (from 250 up to 1100 nm), a reduced HOMO-LUMO gap (1.26–1.68 eV), and a small singlet-triplet energy gap (3.65–5.68 kcal/mol). The rotation of a carbon double bond in an alkene can be efficiently accelerated by creating the high strain ground state and stabilizing the transition state of the process. Here, the authors report the synthesis, structures, and properties of several highly twisted alkenes.