Synthesis and Photophysical Properties of a Series of Dimeric Indium Quinolinates

A novel class of quinolinol-based dimeric indium complexes (1–6) was synthesized and characterized using (1)H and (13)C((1)H) NMR spectroscopy and elemental analysis. Compounds 1–6 exhibited typical low-energy absorption bands assignable to quinolinol-centered π–π* charge transfer (CT) transition. The emission spectra of 1–6 exhibited slight bathochromic shifts with increasing solvent polarity (p-xylene < tetrahydrofuran (THF) < dichloromethane (DCM)). The emission bands also showed a gradual redshift, with an increase in the electron-donating effect of substituents at the C5 position of the quinoline groups. The absolute emission quantum yields (Φ(PL)) of compounds 1 (11.2% in THF and 17.2% in film) and 4 (17.8% in THF and 36.2% in film) with methyl substituents at the C5 position of the quinoline moieties were higher than those of the indium complexes with other substituents.