Effect of cyano substituent on the functional properties of blue emitting Imidazo[1,2-a]pyridine derivatives

High fluorescence efficiency and balanced charge transportation in organic emitters are desirable characteristics for application in OLEDs. Generally, donor-acceptor compounds showing pronounced intramolecular charge transfer exhibit low fluorescence quantum yield. Here, we report D-A fluorophores containing CN-substituted 2-phenylimidazo[1,2-a]pyridine acceptor unit which exhibit good fluorescence characteristics. The positions of donors (triphenylamine/carbazole) and cyano substituents are respectively interchanged to get a series of isomers. All the fluorophores exhibit high fluorescence quantum yield (Phi(f) >= 0.70) and excellent thermal stability (T-d10 >= 390 degrees C). A dye comprising triphenylamine unit at para-position of C2 phenyl ring exhibited red-shifted emission maxima with larger Stokes shift in the series. Moreover, all the isomers displayed excited-state solvatochromism attributable to the photo-induced intramolecular charge transfer between donors and cyano-imidazo[1,2-a]pyridine acceptor. Addition of the cyano group on imidazopyridine restrained the formation of aggregates in the solid-state and stabilized the lowest unoccupied molecular orbital. Among the all, doped devices constructed with 3 wt% of triphenylamine containing dye revealed excellent performance in the series with a maximum EQE of 6.9%, 2759 cd/m(2) luminance, and CIE coordinates (0.16, 0.08) which is very close to the NTSC blue standard.

Automated summary

High fluorescence efficiency and balanced charge transportation are desirable characteristics for organic emitters in OLED applications. This study focuses on D-A fluorophores containing CN-substituted 2-phenylimidazo[1,2-a]pyridine acceptor unit, which exhibit good fluorescence characteristics. The position of donors and cyano substituents were interchanged to obtain a series of isomers. These fluorophores showed high fluorescence quantum yield and excellent thermal stability. Excited-state solvatochromism and aggregation suppression were observed in the isomers due to the photo-induced intramolecular charge transfer. Doped devices with triphenylamine-containing dye showed excellent performance in terms of EQE, luminance, and CIE coordinates.