A novel hyperbranched copolymer, poly(2,4,6-tributyloxy-1,3,5-trivinylenephenylene-co-2methoxy-5-octyloxy-p-phenyelenevinylene) PTBOTV-co-PMOPV, and a linear counterpart poly(2-methoxy-5octyloxy-p-phenyelenevinylene) (PMOPV) were synthesized by the Gilch polymerization and characterized with UV-vis, FT-IR, 1 H NMR and Photoluminescence (PL) spectroscopy. PTBOTV-co-PMOPV showed excellent solubility, good film-formation ability, and high thermal stability. The UV-vis, PL, and electroluminescence (EL) spectra of PTBOTV-co-PMOPV were blue-shifted approximately 9-15 nm on comparison with those of PMOPV. The polymer light-emitting diode (PLED) was fabricated in ITO/PEDOT (50 nm)/polymer (60 nm)/ Alq 3 (30 nm)/LiF (1 nm)/Al (200 nm) configuration. The PTBOTV-co-PMOPV exhibited the maximum external quantum efficiency (EQE) of 0.26% at 60.7 cd/m 2 , while the PMOPV device showed the maximum EQE of 0.17% at 88 cd/m 2 .
The molecular structures of 1, 8-naphthalimide derivatives were investigated at density functional theory level within framework of PBE1PBE/6-31G*. The vertical ionization potential and their delocalization energy of the X-ray solid structure and gas-phase optimized structure were explored. The configuration difference between them was attributed to the p-p interaction of the solid effect, which has negligible effect on their absorption spectra. Solid effect also weakens the intramolecular interaction. Their absorption and luminescent spectra in gas and solvent phase were calculated by time-dependent density functional theory (TDDFT) and conductor polarizable continuum models (CPCM)-TDDFT approaches. Obvious red shifts from the solvent effect were found. Substituents on the imides will not improve their spectra properties a lot, whereas substituents on the naphthalene of naphthalimide would modify their properties to emit different spectra. Systematical deviation of vertical excitation energy from absorption and emission spectra, obtained by CPCM-PBEPBE/6-31G* and CIS-CPCM-PBEPBE/6-31G* models, were about 0.05 eV and 0.02 eV compared with the experimental values.
Using TD-PBE1PBE/6-31G* and TD-B3LYP/6-31G* approaches, we calculated the absorption and emission spectra of 1,8-naphthalmide derivatives in gas-phase. The geometric structures optimized by HF/6-31G* and B3LYP/6-31G* models and the absorption and emission maxima were in good agreement with existed experimental measurements. It was also found that the lowest singlet states corresponded mainly to the electronic transition from the highest occupied orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO). Intramolecular charge transfer occurred between substituents and naphthalimic rings. Study also showed that most compounds with low absorption excitation energies had low vertical ionization potentials. Finally, the delocalization electronic energies between substituents and naphthalimic rings of isomers were investigated to obtain further sight into their stability.
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