A new type of light-emitting naphtho[2,3-c][1,2,5]thiadiazole derivatives: synthesis, photophysical characterization and transporting properties

We report a new series of naphtho[2,3-c][1,2,5]thiadiazole (NTD) derivatives which present both carrier transporting property and high fluorescence quantum yield. Optical absorption and emission property, film morphology and thermal stability of these compounds have been investigated. Due to the absence of a strong donor group in the molecular structure, intermolecular dipole–dipole interaction and concentration quenching are effectively suppressed. The emission color was found to be adjustable depending on the aryl substituents at the 4,9-position of the NTD chromophore. Single crystals of 4-(2,2-diphenylvinyl)phenyl-substituted NTD (1) and biphenyl-substituted NTD (3) were obtained and determined by X-ray crystallography. It was found that 1, 3 and 2-naphthalene-substituted NTD (5) show ambipolar transporting property with almost identical hole and electron mobilities. Notably, 1 shows extremely high transporting ability, whose hole and electron mobilities were measured to be 7.16 × 10−4 and 6.19 × 10−4 cm2 V−1 s−1 at an electric field of 2.0 × 105 V cm−1, respectively. Theoretical calculations showed 1, 3 and 5 have similar reorganization energies for holes and electrons, and holes and electrons would both hop between the adjacent NTD chromophores, resulting in the ambipolar transporting property. Double-layer non-doped devices were fabricated with some of the NTD derivatives, and the correlations between device performance and molecular structure were also discussed.