Synthesis and light-emitting properties of difunctional dendritic distyrylstilbenes

A novel series of poly(benzyl ether) type dendritic distyrylbenzenes bearing various electron or hole affinitive moieties including 1,3,4-oxadiazole, cyano, and propoxy groups on the outer surface of the first- and second-generations dendritic wedges have been synthesized for blue-light emission. Both theoretical and optical studies show that incorporation of the surface functionalized dendritic wedges into the nonconjugated meta positions of a distyrylstilbene skeleton does not disrupt the coplanarity of the 7-conjugated core. Excitation of the surface functionalized dendritic wedges leads to substantial energy transfer from the dendritic wedges to the emissive core (up to 59%). Importantly, all the dendritic distyrylstilbenes show very high fluorescence quantum yields (over 93%). Single-layer light-emitting diodes (LED) using dendritic distyrylstilbene (DSB) doped poly(N-vinylcarbazole) (PVK) film as an emissive layer with structure of (ITO/DSB:PV-K/Al) have been fabricated and investigated. The emission wavelengths and spectral features are very similar among the solution emission, solid-state photoluminescence, and electroluminescence spectra. The device performance of the first-generation dendritic DSB doped single-layer LEDs is generally superior to that of the corresponding second-generation dendrimer based devices. In addition, the propoxy surface functionalized dendritic DSB devices consistently show the best device performance and relative stability among the others.