This work reports on a quinodimethane-type molecule, 2,7-dicyanomethylene-9-(2-ethylhexyl)carbazole (1), one of the shortest -conjugated biradicaloids reported to be stable in solution under ambient conditions. This carbazole-based quinoidal precursor is able to form a macrocyclic sigma-bonded tetramer (2). The resolved single-crystal X-ray structure of tetramer 2 shows that four molecules of 1 are linked together through four long (CN)(2)C-C(CN)(2) bonds (1.631 angstrom) resulting from coupling of the unpaired electrons in biradicaloid 1. Dynamic interconversion between monomer 1 and cyclophane tetramer 2 is achieved by reversible cleavage and recovery of the four (CN)(2)C-C(CN)(2) bonds upon soft external stimuli (light absorption, temperature and pressure), which is accompanied by significant color changes. These novel photo-, thermo-, and mechanochromic properties expand the versatility of pi-conjugated biradicaloid compounds as novel functional materials that, in combination with spin chemistry and dynamic covalent chemistry, can be relevant in molecular machines, sensors, and switches.
[1]Chinese Acad Sci, Key Lab Synthet & Self Assembly Chem Organ Funct, Shanghai Inst Organ Chem, 345 Lingling Rd, Shanghai 200032, Peoples R China;
[2]Univ Malaga, Dept Phys Chem, Campus Teatinos S-N, Malaga 229071, Spain;
[3]Fudan Univ, Lab Adv Mat, 200 Handan Rd, Shanghai 200438, Peoples R China;
[4]Univ Complutense Madrid, MALTA Consolider Team, Dept Phys Chem, Madrid 28040, Spain;
[5]Univ Reading, Dept Chem, Reading RG6 6AD, Berks, England
(8.0+极速模式)