Synthesis and Properties of Triptycene-Diaminostilbene Hybrid Systems

The synthesis, electronic spectra, and thermal and electrochemical properties of two triptycene-capped trans-4,4′-diaminostilbenes (1Me and 1Ph) are reported in order to evaluate their applicability as blue light-emitting materials in organic light-emitting diodes (OLEDs). For comparison, the fluorescence properties of the planar analogs 2Me and 2Ph are also investigated. High fluorescence quantum yields (0.72–0.78) are observed for 1Me and 1Ph in THF, presumably due to a large barrier for the nonradiative double-bond torsion reaction in the singlet excited state. In the spin-cast thin films, the fluorescence quantum efficiencies become lower (0.15–0.26) and the fluorescence spectra are red-shifted. Compared to 1Me and 1Ph, 2Me and 2Ph display even larger fluorescence shifts and fluorescence quenching, which can be attributed to their more planar structures that favor intermolecular π-stacking in the solid state. The glass transition temperatures for 1Me and 1Ph are 113 and 120 °C, respectively, and the decomposition temperatures 341 and 375 °C, respectively. Cyclic voltammograms of 1Me and 1Ph show two reversible redox waves, corresponding to two monoelectronic oxidation processes of the amino groups forming radical cation and dication species.