4,7‐Bis[3‐(dimesitylboryl)thien‐2‐yl]benzothiadiazole: Solvato‐, Thermo‐, and Mechanochromism Based on the Reversible Formation of an Intramolecular B−N Bond

• Published in: Chemistry : a European journal Vol. 23; no. 15; pp. 3784 - 3791
• Main Authors: Shimogawa, Hiroyuki, Yoshikawa, Osamu, Aramaki, Yoshitaka, Murata, Michihisa, Wakamiya, Atsushi, Murata, Yasujiro
• Format: Journal Article
• Language: English
• Published: WEINHEIM Wiley 13.03.2017; Wiley Subscription Services, Inc
• Subjects: Bonding; Boron; Chemical bonds; Chemistry; Chemistry, Multidisciplinary; coordination bonds; Derivatives; Exact solutions; Formations; Mathematical analysis; mechanochromism; Physical Sciences; Science & Technology; solvent effects; steric effects; Synthesis; ORGANOBORON COMPOUNDS; solvent effects; mechanochromism; CRYSTAL PHASE-TRANSITION; coordination bonds; BAND-GAP; steric effects; ELECTRON-AFFINITY; MOLECULAR DOMINO; COORDINATION-NUMBER; CONTAINING POLYMERS; LIQUID-CRYSTALS; AUROPHILIC BONDS; boron
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201606041

4,7‐Bis‐[3‐(dimesitylboryl)thien‐2‐yl]benzothiadiazole (1) and monoborylated derivative 2 were synthesized and their chromic behavior was investigated. Photophysical measurements, single‐crystal XRD analysis, and theoretical calculations revealed that an intramolecular B−N coordination bond formed reversibly. The equilibrium of this reversible bond formation depends on the solid‐state structure, solvent, temperature, and mechanical forces, and leads to significant changes in the electronic structure and chromic behavior of these molecules. The responsiveness toward external stimuli, resulting in the reversible formation of open and closed forms of this system, is achieved through weak intramolecular B−N coordination bonds induced by the steric bulk of the mesityl groups on the boron centers. Changing colors: A dimesitylboryl (Mes2B)‐substituted benzothiadiazole derivative, exhibiting chromic behavior, was designed and synthesized. A set of experiments and theoretical calculations revealed that the chromic phenomena were induced by the reversible formation of an intramolecular B−N coordination bond (see figure). This reversibility of bond formation is induced by the steric bulk of the Mes groups on the boron centers.