Design,Synthesis And Properties Of E/Z Isomers Based On Cyanostilbene

Organic luminescent materials have developed rapidly in recent years and have been widely used in many fields.Small organic luminescent molecules containing C=C double bonds units are important components of organic luminescent materials.But the E/Z isomerization reaction is founded extensively in most organic molecules containing double bond units.That's limits their practical application as luminescent materials partly,especially under photo-irradiation condition.Therefore,it is very important to obtain E/Z isomers with stable configuration in the excited state under photo-irradiation condition.Tetraphenylethene(TPE)derivatives and cyanostilbene(CNS)derivatives play an important role in organic photoelectric materials fields.At present,most reports focus on tetraphenylethylene derivatives,which might because CNS derivatives are less stable than TPE derivatives.However,due to the strong electron accept ability and large steric hindrance effect of CNS unit substituted cyano-group on C=C double bonds,it is beneficial to the formation of donor-acceptor(D-A)structure and intermolecular charge transfer.We make a studied about some molecules based on CNS unit,reported a triphenylamine-cyanostilbene molecule(TPNCF)formed by modifying the CNS structure with triphenylamine,which could maintained the stable E/Z configuration as the film in high polar solvents.We proposed that the charge transfer(CT)excited state between the triphenylamine donor and cyanostilbene acceptor groups induced the stable configuration of the E-and Z-isomers under photo-irradiation.According to our study,the E/Z isomerization process occurring at a higher energy locally excited(LE)state was suppressed by a rapid internal conversion process from the LE to CT state under irradiation,which effectively solves the problem of poor stability of CNS group.In the first part of the thesis,a donor-acceptor(D-A)phenoxazine-cyanostilbene molecule(PZNCF)was designed and synthesized.By contrast to the triphenylamine-cyanostilbene molecule(TPNCF),the in-situ NMR and UV spectra of E-and Z-isomers of PZNCF demonstrated that the E/Z isomerization rate become slower under photo irradiation,which indicated that the stronger electron donating group of phenoxazine substituted in cyanostilbene structure was benefit to the configuration stability of E/Z isomers.DFT calculation and photophysical results indicated that a stronger charge transfer state was generated in both E-and Z-isomers of PZNCF,which indicated that the modification of D-A group to make the molecule have a low energy strong CT state was cond ucive to the the stability of CNS derivatives.In the second part of the thesis,two pairs of D-A phenooxazine-cyanostilbene molecules were designed and synthesized(E/Z-PZNCF and E/Z-PZNC),the four target molecules were successfully characterized by NMR and X-ray single crystal diffraction.The E/Z configuration stability of E/Z-PZNCF and E/Z-PZNC molecules was compared by in-situ ~1H-NMR spectroscopy and in-situ UV-vis spectroscopy.The results showed that the E/Z isomerization rate of E/Z-PZNCF molecule containing trifluoromethyl substituted cyanostilbene was significantly slower under the condition of light irradiation,which indicated that stronger electron acceptor were more conducive to the stability of E/Z configuration in the D-A molecule system based on CNS.DFT calculation and spectral experiment results showed that both E-isomer and Z-isomer of PZNCF had stronger CT states compared with PZNC,which is consistent with the result in previous part.In the third part of the thesis,two D-A cyanostilbene derivatives with AIE activity were designed and synthesized,abbreviated as PZPNC and PZNC,whose chemical structures only differ by one more phenyl between donor and acceptor.Their E/Z isomers were characterized with single crystal structures and the effect of D-A distance on the stability of E/Z configuration was studied.The in-situ UV-vis spectra and HPLC spectra of E/Z-PZPNC and E/Z-PZNC under photo-irradiation demonstrated that the E/Z isomerization of PZNC was slower than PZPNC,indicating that the shorter D-A distance is conductive to the stability of CNS derivatives.According to the above studies,the stable E/Z configuration can be obtained by designed and synthesized a reasonable D-A structure.The E/Z isomerization process occurring at a higher energy locally excited(LE)state could be suppressed by a rapid internal conversion process from the LE to CT state under irradiation.This guideline should be further developed in other molecular structure design with double bond to achieve more configuration-stable molecules for organic photo-electronic applications.