Strongly luminescent and liquid-crystalline π-conjugated 2-methyl[1,2,3]benzotriazoles with a linear donor-acceptor-donor structure

Symmetrical 2-methyl[1,2,3]benzotriazole (BZT) derivatives with elongated peripheral units connected via acetylenic triple bonds present calamitic thermotropic mesomorphism with nematic and smectic phases. They show intense photoluminescence with near-unity quantum yields in solution. The peripheral groups significantly influence the excited-state lifetime. Fluorescence quenching is observed in the presence of C60, testifying of charge transfer to the fullerene acceptor. The varying sterical demand of the different substituents considerably influences the efficiency of the charge transfer induced fluorescence quenching. HOMO, LUMO and band gap energies ranged from −5.15 to −5.97 eV (ionization potential), −2.47 to −2.96 eV (electron affinity) and 2.68 to 3.08 eV (optical band gap).