Synthesis And Application Of Selenophenol Based Triplet Photosensitizers

The chromophore that called triplet photosensitizer can generate triplet state with high-efficiency through intersystem crossing after being excited.It has a wide range of applications,including electroluminescence,bioimaging,photodynamic therapy,and triplet-triplet annihilation upconversion and so on.Intersystem crossing is a spin-forbidden process,so the difficulty of designing new triplet photosensitizers is to extend the triplet lifetime of the photosensitizer while retaining strong absorption ability for visible light.At present,triplet photosensitizers are consisted of triplet photosensitizers based on heavy atoms and photosensitizers without heavy atoms.Transition metal complexes and photosensitizers substituted with iodine or bromine atoms belong to triplet photosensitizers based on heavy atoms.Various reaction mechanisms such as exciton coupling,introduction of spin converters and n-?*transitions were involved in the photosensitizers without heavy atom.Since mechanisms of the photosensitizer without heavy atom are numerous and complex,selenophenol was used as the heavy atom group in this paper to design triplet photosensitizers such as fluoroboron dipyrrole photosensitizers and phenothiazine photosensitizers,aiming to explore the influence of selenophenol on the photophysical properties of photosensitizer.Specifically,the research content of this article includes:(1)Using the fluoroboron dipyrrole(BODIPY)as the chromophore,and selenophenol as the heavy atom group,photosensitizers MB-Se,2B-Se and MB-Se-2Br were synthesized.Compared with BDP-2I,the three photosensitizers all had medium or even excellent absorption ability for visible light,and a significant bathochromic shift of its spectrum with the extension of?-conjugation.Possessing a large Stokes shift was one of the characteristics of the three photosensitizers.The obvious separation of absorption and emission facilitated its elimination of background light interference in biological imaging.An A-D-A structure was formed between selenophenol with the BODIPY because selenophenol was a donor with weak electron-donating ability,then ICT phenomenon was apparent.Selenophenol was introduced to BODIPY with alkynyl group enabled selenophenol to participate in the formation of the triplet state of BODIPY effectively,then the fluorescence of the BODIPY was quenched obviously,and the triplet lifetime of 22.8?s,13.1?s,and 17.2?s were finally obtained.In addition,singlet oxygen can be effectively obtained by photosensitizers MB-Se,2B-Se and MB-Se-2Br.The singlet oxygen quantum yield were determined as 90.4%,39.1%and 97.2%of photosensitizers MB-Se,2B-Se and MB-Se-2Br using rose bengal as the standard,respectively.However,the loss of excited state energy with the rotation of the central benzene ring should be responsible for the short triplet lifetime and low singlet oxygen quantum yield of the photosensitizer 2B-Se.With photosensitizer MB-Se-2Br as the energy donor and perylene as the acceptor,the upconversion efficiency of 3.3%was finally obtained.(2)Using phenothiazine as the based molecule,electron-withdrawing groups were introduced to the 10^th position of phenothiazine to construct a D-A structure molecule with non-planar configuration,generation of triplet excitons can be improved while using D-A structure and the n-?*transition of lone pair of electrons in S and N atoms in phenothiazine.At the same time,selenophenol was introduced into the benzene rings on both sides of phenothiazine to enhance the degree of spin-orbit coupling,then molecules PTZ-Se-ACN and PTZ-Se-CF₃ were synthesized,and the corresponding photophysical properties were tested.The intramolecular charge transfer between phenothiazine and acceptors were greatly destroied with the introduction of selenophenol,and finally only LE absorption band was detected near 260 nm,solvation phenomenon disappeared at the same time.Similar to the heavy atom effect of the bromine atom,the molecular fluorescence were effectively quenched by selenophenol,then microsecond lifetime were obtained in the deoxygenation solution at room temperature.Comparing the luminescence spectra in deaeration solution at room temperature and 77 K,it was confirmed that only ³LE emission were maintained in PTZ-Se-ACN and PTZ-Se-CF₃.PTZ-Se-ACN and PTZ-Se-CF₃ were confirmed as room temperature phosphorescent molecules by spectrums and decay curves at different temperature.