| In recent years,with the rapid development of science and technology,and scientists constantly explore the photochemical field in depth,organic photochromic compounds have rapidly become active research field.Common organic photochromic molecules include fulgide,diarylethene,azobenzene and spiropyran etc.Among these compounds,fulgide and diarylethene as typical photochromic molecules have been widely applied in molecular switch and optical data memory due to their excellent fatigue resistance,good thermal stability and rapid response.They mainly exist two isomers,including ring-closed and ring-opening isomer,and they can proceed a reversible conversion each other by irradiation with appropriate absorption wavelength.Based on these attributes,they often act as important units for the design of multi-functional molecular switches.Thus,the studies of organic photochromic molecules have important theoretical value and practical significance.In this thesis,we discuss the ground state geometries and low-lying excited state properties of furylfulgides and diarylethene derivatives by using density functional theory(DFT)and time dependent density functional theory(TDDFT)methods.The studies of furylfulgides mainly focus on the absoption properties and design of multi-functional molecular switches,and diarylethene derivatives mainly center on the discussions of nonlinear optical(NLO)properties.The main contents are concluded as follows.1.Theoretical investigation on the spectroscopic properties of furylfulgide with different substituents and design of novel bis-furylfulgimide photochromesDue to the shorter absorption wavelength,ring-opening and ring-closed furylfulgide isomers have limited applicability in the optoelectronic devices,especially for semiconductor devices.Accordingly,we discuss the effect of different substituents on the geometries and optical properties of furylfulgides by using DFT and TDDFT methods.We notice that amino substituted ring-closed isomer exhibits obvious red shift of wavelength at the R3 position,moreover,it owns the maximum difference of absorption wavelength between ring-closed and ring-opening isomers.Thus,it is hopeful to act as the excellent candidate of molecular switch.Based on the aforementioned work,we further design nine bis-furylfulgimide dimers(BFF: 1-9)by the combination of different furylfulgimide monomers and discuss their spectral properties.The results reveal that the asymmertrical BFF-6 dimer exhibits the most potential for photoisomerization.Hence,we discuss the photoisomerization mechanism of BFF-6 dimer in detail from a theoretical perspective.2.Theoretical investigation on photoswitchable second-order nonlinear optical properties of a series of B(C6F5)2-coordinated dithienylethene derivativesIn this thesis,we calculate the static first hyperpolarizabilities(?tot)for some B(C6F5)2-coordinated dithienylethene derivatives,which have been synthesized by experimental methods.We find that 2-B(C6F5)2 molecule exhibits excellent NLO responses.Based on this work,we introduce a simple N=N-ph ligand and discuss the influence of electron-donating and electron-withdrawing ability on their NLO behaviors.The results show that the ?tot values of ring-opening and ring-closed isomers dramatically increase with the increasement of electron-donating and electron-withdrawing ability.Moreover,the calculated ?tot values of ring-closed isomers are larger than those of the corresponding ring-opening isomers,it is mainly attributed to the forming of a larger ?-conjugation in the ring-closed isomers.The ring-closed isomer 5c owns the largest ?tot values(7361.4 × 10-30 esu),which is 29.8 times larger than that of the corresponding ring-opening isomer 5o.Besides,we also calculate the absorption spectra and relative frontier molecular orbitals by TDDFT method.At last,we discuss the influence of dispersions on the frequency-dependent first hyperpolarizabilities(?tot(?))at the low-frequency region ?(0.000-0.065 a.u.). |
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