| Photochromic materials,due to their novel optical properties,have attracted a lot of attention since they were synthesized and used into practical application.Among various of photochromic materials,the treated representative one is diarylethene.A reversible photocyclization and photocycloreversion for diarylethene can proceed under different wavelength irradiation,which makes an exchange between open-ring or closed-ring isomers.The isomers show the same favourable thermal stability but different behaviours in absorption,solvent colour,electric conduction,fluorescence and so on.These special behaviours impel diarylethene to be widely applied in optical instruments,such as information transfer,data storage,molecular switch,fluorescence label,etc.In this job,we systematically have a calculation on two kinds of diaryletnenes,bis(3-thienyl)/(2-thienyl)hexafluorocyclopentene.By analysis on their structures,frontier molecular orbitals,absorption and emission spectra,we try to give an intrinsic explanation on their excited state properties and the mechanism of photo/electrochromism performance.Moreover,according to our results,we have designed a series of new compounds that may have better hehavior in photo/electro physical and chemical properties,which can give a guidance on the practical application of diaryletnene.This paper comsists five chapters.In chapter 1,a summary of the basic description on the fundamental principles of photochromic materials,expecially to the properties of diarylethene.In chapter 2,an overview of theoretical methods including the basic theory of quantum mechanics and the quantum chemistry calculation method including CIS,perturbation theory,and DFT is introduced.In chapter 3-5,inductions about our jobs on diarylethene are proposed.Detailed contents are described as below.1.Density functional theory(DFT)calculations are utilized to analyze a novel S,S-dioxide diarylethene of which,contrary to general ones,ring-closing happens under visible light(436 nm)and ring-opening arises in ultraviolet light(365 nm).The asymmetrical structure and the oxidized S atoms alter the continuity and switch way of conjugation system between two isomers.The role and position of substituent affect the electron transfer pattern in isomerzation and result in changes in conversion ratio and quantum yield.Based on the diarylethene,we designed new dyads in which ring–closing and-opening of the two diarylethene parts in one molecule proceed simultaneously under single wavelength.The photocyclization on one part of the molecule does not limit but facilitate the photocycloreversion on the other part.2.a series of bis(3-thienyl)/(2-thienyl)hexafluorocyclopentene is calculated using DFT method about their electrochromism.Under redox state,the gain or loss of electrons can give significant effect on the frontier molecular orbitals distribution of both open-and closed-ring isomers,especially in reactive site.Corresponding structural change shows a trend directing to isomerization.Reaction energy barrier reduces more in dication than in monocation and even becomes barrierless in dianion.During the isomerization in different states,the conjugated system switches distinctively,which is attributed to the special redistribution of molecular orbitals and spin population in each state.In monocation and monoanion,for the involvement of single electron,isomerization inclines to proceed sequentially between right and left thienyls,whereas it turns synchronous in dication.The direction depends on the stabilization achieved by the formation of global conjugated system and more average spin population on the molecule.The effect of substituent on thienyls shows on the promotion to the extent of conjugation and determination of the spin population level on the reactive C atoms.Moreover,according to their electron-donating and withdrawing ability,they can support or suppress the electron transfer pattern in the process from isomer to transition state kinetically,which leads to a control of reaction efficiency.3.A theoretical comparison about the photophysical and photochemical properties has be made among a series of diarylethene-containing Pt(II)complexes It is found that the extension of conjugated systems and electron-withdrawing substitute on host-ligand promote the rigidity of structures,which is beneficial to the electron transfer during excitation.Moreover,the phosphorescence emission and quenching of complexes can be controlled by utilizing the contrary optical performance of their two isomers.In closed-ring forms,the complexes suffer a phosphorescence quenching for the inefficient involvement of Pt in the excitation and the low energy gap between first triplet excited state and ground state.In open-ring forms,the shift of conjugated systems makes the excitation switch from diarylethene to Pt so that spin–orbit coupling effect can be achieved,which leads to an effective phosphorescence emission.In addition,calculation of radiative decay rate is proposed to give an evaluation of the radiative decay process of open-ring forms.And the analysis on the potential energy surface of triplet excited state presents an in-depth description about the role of isomerization in their nonradiative decay process.All of results above manifest the tunability and applicability of diarylethene in organometallic materials.Based on it,new complexes have been designed as promising candidates with better photoresponsive and phosphorescent performance. |
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