Synthesis and Luminescence Properties of Dithieno[3, 2-a:2', 3'-c］Phenazine Derivatives with Electron-Donating π-Conjugated Side-Arms at the 2, 5-and 8, 11-Positions

摘要

Two types of novel dithieno[3, 2-a:2', 3'-c]phenazine (dtpz) derivatives, bearing electron-donating π-conjugated side-arms at the 2, 5-and 8, 11-positions, were synthesized and their luminescence properties were discussed. The 8, 11-disubstituted derivatives exhibited fluorescence in dichloromethane in the regions from yellow to red (photoluminescence wavelength λ_PL;557-651nm) . Especially, 9- (2-ethylhexyl) -9H-carbazo1-3-yl and 4-hexylthiophen-2-yl side-arms afforded red emission with high photoluminescence quantum yields (Φ_PL) of 0.75 (λ_PL;616nm) and 0.38 (λ_PL;651nm), respectively. Although the 2, 5-disubstituted derivatives (λ_PL;630-685nm) exhibited more red-shifted fluorescence in dichloromethane than the 8, 11-disubstituted derivatives, they are less emissive, showing Φ_PL of 0.07-0.23. All the developed dtpz derivatives showed positive solvatochromic behavior in photoluminescence, and red shifts of their photoluminescence spectra were observed as polarity of the solvent increased. From the Lippert-Mataga plots, their dipole moments were significantly enlarged upon photoexcitation, indicating that strong intramolecular charge transfer occurs upon electronic transition. Using the 8, 11-disubstituted dtpz derivative with 9- (2-ethylhexyl) -9H-carbazol-3-yl side-arms as an emitting dopant, a poly (9-vinyl-9H-carbazole) (PVCz) -based OLED was fabricated. Yellow electroluminescence with the Commission Internationale de L'éclairage chromaticity coordinate of (0.53, 0.46) was observed, the spectrum of which was blue-shifted in comparison with photoluminescence of the emitting dopant in dichloromethane due to low polarity of the PVCz host.