| In this thesis, five kinds of intramolecular charge transfer (ICT) compounds with benzohetercyclic structures as acceptor parts and phenoxazine (PXZ)/phenothiazine (PTZ) as donor parts were synthesized. Their structures were characterized by single crystal X-ray diffraction, NMR, MS and infrared spectroscopy. The luminescent properties were determined by UV-Vis absorption spectra, fluorescence spectra, luminescent lifetime and quantum yield measurements. Quantum chemistry calculation with Gaussian was employed to elucidate the luminescence mechanism and energy gaps between different excited states. Main results in this paper are summarized as follows:1. A new twisted intramolecular charge transfer (TICT) compound PPBI-PXZ was synthesized by the Buchwald-Hartwig reaction of 2-(4-bromophenyl)-1-phenyl-1H-benzimidazole (PPBI-Br) with PXZ. Single crystal X-ray diffraction showed that there was a structural deformation between the PXZ unit and the acceptor unit with a dihedral angle of 78.8°. In n-hexane, toluene, ethyl acetate, dichloromethane and acetonitrile, PPBI-PXZ solutions had an absorption shoulder at 370-420 nm which could be assigned to intramolecular charge transfer (ICT), and emitted light with maximun wavelengths at 419 nm,471 nm,509 nm,534 nm and 577 nm, respectively. These demonstrated that PPBI-PXZ had an obvious solvatochromism. PPBI-PXZ exhibited great thermal stability with a decomposition temperature of 466 ℃, suggesting that PPBI-PXZ was a stable TICT compound.2. Four kinds of TICT compounds were synthesized with 2-phenylbenzoxazole (PBO)/2-phenylbenzothiazole (PBT) as acceptors and PXZ/PTZ as donors. Single crystal X-ray diffraction showed that all the four compounds had twist structures, among which the dihedral angle between PTZ and acceptors was almost orthogonal because of the steric repulsion of PTZ with a butterfly structure. Four compounds had obvious solvatochromism. The toluene solutions of compounds with PXZ exhibited considerable luminescent properties with microsecond emission lifetimes. In the absence of oxygen, the photoluminescence quantum yields (PLQYs) (0.55 and 0.27) of the solutions presented significant improvement compared with those (0.30 and 0.16) in air. The energy gaps (△EST) between the S1 state and T1 state of the compounds with PXZ were 0.13 eV and 0.17 eV according to the fluorescence spectra and phosphorescence spectra. These indicated that the two compounds had the properties of thermally activated delayed fluorescence (TADF).3. Quantum chemistry calculations with Gaussian indicated that the highest occupied molecular orbital (HOMO) states of the four compounds were mainly distributed on the donor units and the lowest unoccupied molecular orbital (LUMO) states were localized on acceptor units. There were obvious ICT between donors and acceptors. The changes of the charge transfer amount (q) and energy gaps between HOMO state and LUMO state by quantum calculation accorded with the analyses about solvatochromism and UV-Vis absorption spectra. △EST of four compounds were calculated through a method reported by Zhang. The calculation results showed that two compounds with PXZ had small calculated △EST (0.01 eV), suggesting they could achieve reverse intersystem crossing (RISC) from T1 state to S1 states at room temperature. Since the calculation results were agree with the experimental data approximately, the used calculation method was further employed to select and predict the energy gap and emitting wavelength of new designed structures. Three 1,8-naphthalimide derivatives with different aniline donors were simulated by that method. As a results, △EST of the compound with PXZ as a donor is only 0.023 eV and its initial emitting wavelength of polar solution was estimated at 629.8 nm. Thus this structure may be a candidate for TADF material of red photoluminescence, which was seldom reported. The quantum calculations may afford to explore D-A luminescent materials. |
PDF Full Text Request