Design,Synthesis And Properties Of Photochromic Compounds Based On Porphyrins

During the isomerization process of photochromic compounds,the change of chemical structure results in the significant changes of the absorption spectra,the photophysical and photochemical properties of compounds,such as dielectric constant,refractive index,fluorescence,redox potential etc.Among these outputs,fluorescence is considered as one of the most promising application for optical molecular switches and optical information storage owing to its fast response time,low device cost and easy operation.In recent years,photochromic dithienylethenes and fulgides have aroused surge of interest with their excellent thermal stability and fatigue resistance properities.In this paper,a series of dithienylethenes and fulgides modified with porphyrins were designed and synthesized,their structures were characterized and their photochromic properities were discussed.Two novel fulgides based on thiophene and thiazole were synthesized and the thienylfulgide show excellent photochromic reactivity in both solution and solid state.The maximum absorption peaks of its open and closed form are located at 326 and 498 nm respectively.The closed form can be stable for a long time in the environment of 120 ?,indicating that it has nice thermal irreversibility and thermal stability.The thienylfulgide still show good photochromic reactivity after repeat irradiation of ultraviolet and visible light for 50 times,indicating that it possesses excellent fatigue resistance.The photocyclization and photocycloreversion quantum yield are 0.21 and 0.13 respectively.The density functional theory(DFT)calculations at B3LYP/6-31G(d.p)theoretical level were employed to investigate the nonlinear parameter of thienylfulgide.Its calculated value is very closed to the experimental value,indicating that this method will be very useful to predict the properties of such fulgides.The dipole moment,polarizability and the total hyperpolarzability of C-configuration are 0.271 less,7.05 more and 4.9 times more than the E-configuration,indicating that it has excellent nonlinear optical properties in theory.A novel fulgimide based on tetraphenylporphyrin and its metal complexes were synthesized,they show good photochromic reactivity while upon with the irradiation of ultraviolet and visible light.The maximum absorption peak of the closed form redshifts 169 nm compared to the fulgide,the Soret band of porphyrin moiety also redshifts.The photo quantum yield and molar absorptivity increased when porphyrin was linked,but decreased when metals are introduced.The open form of porphyrinic fulgimide emits fluorescence at 629 nm when excited with light of 520 nm,and the closed form does not.Furthermore,when metals are introduced,their fluorescence all quench.A series of novel asymmetric dithienylethene compounds have been designed and synthesized,and they possess good photochromic reactivity and fatigue resistance upon irradiation with ultraviolet and visible light.The maximum absorption peaks of the open and closed form will redshift when aryl groups are introduced,and their photocyclization quantum yield are closed to 0.5,the photocycloreversion quantum yield are no more than 0.25.The introduced of aryl groups and electron-donating groups will improve the thermal stability of the closed form.Among them,the diaminophenylditheinylethene shows the best thermal stability,its fatigue resistance time can be up to 43 h.A series of novel asymmetric pyridyldithienylethenes coordinating with metal porphyrins have been designed and synthesized,and they possess good photochromic reactivity and fatigue resistance upon irradiation with ultraviolet and visible light.The introduction of metal porphyrin make the maximum absorption peaks of the closed form redshift obviously and have influence on the Soret band of porphyrin moiety.The substituent effect of porphyrin on the absorption spectra of dithienylethene unit is not obvious.The open and closed form of them can all emit fluorescence when upon with appreciate light which does not result in the cyclization and cycloreversion,indicating that these compounds have the potential to be used in the optical information storage.The photocyclization quantum yield have been improved when the pyridyldithienylethenes is coordinated with metal porphyrins,while the photocycloreversion quantum yield remain unchanged.In the hot solution,the coordination bond is easily to be broken,and it will self assembled into the original structure while cooling down.A novel amide linked porphyrin and dithienylethene photochromic compound was designed and synthesized,it shows obvious photochromic reaction upon irradiation of ultraviolet light of 365 nm,its dichloromethane solution changes from pale pink to yellow green while the Soret absorption peak of the porphyrin unit red shifts from 418 nm to 450 nm,the Q band absorption peaks gradually disappear,and a new absorption peak at 671 nm appears.The open and closed form all show obvious different fluorescence when excited with light of 418,450 or 530 nm which do not result in the cyclization and cycloreversion,indicating that this compound is expected to be used in the light information storage device.The photocyclization quantum yield increased from 0.48 to 0.51 and the thermal stability is also improved significantly,fatigue life increased from 7 h to 17 h compared to the dithienylethene monomer.A novel porphyrinic dithienylethene photochrome was designed and synthesized through the Suzuki reaction by bromo-phenyldithienylethene and iodo-tetraphenylporphyrin as raw materials,it shows obvious photochromic reaction upon irradiation of ultraviolet light of 365 nm,its dichloromethane solution changes from pale pink to yellow green while the ultraviolet absorption peak at 272 nm decreased,and the Soret band of the porphyrin unit red shifts from 418 nm to 446 nm,the Q band absorption peaks gradually disappear,and a new absorption peak at 670 nm appears.The open and closed form showw obvious different fluorescence when excited with light of 418 nm which does not result in the cyclization and cycloreversion,indicating that this compound is expected to be used in the light information storage device.The photocyclization quantum yield increased from 0.26 to 0.49 and the thermal stability is also improved significantly,fatigue life increased from 12 h to 23 h compared to the dithienylethene monomer.Moreover,no matter in the acid or alkaline system,this compound can maintain its excellent photochromic properties.In summary,this paper designed and synthesized the new fulgimides and dithienylethenes containing porphyrin units,these compounds not only have good photochromism,but also have good fatigue resistance,better thermal stability and higher photocyclization quantum yield.Under the excitation of the appropriate light source,the fluorescence spectra of the open and closed isomers of these compounds show obvious difference,and the excitation light dose not cause the ring-close and ring-opening reactions.Therefore,these compounds are expected to be used in optical information storage devices,to achieve the nondestructive readout of information.