Design,Synthesis And Application Of Triplet Photosensitizer Based On Squaraine Dyes

Organic triplet photosensitizers have been widely used in different fields,such as:photodynamic therapy,photoinduced catalytic hydrogen production,triplet-triplet annihilation up-conversion,photo-redox organic reaction,oxygen sensing and so on.However,there are still some limitaions in the design of existing organic triplet photosensitizers,such as weak absorption of light in the near-infrared region by molecules,mainly relying on heavy element modification,and low triplet quantum yield.In this article,in order to further enrich the diversity of triplet photosensitizers,two series of triplet photosensitizers were synthesized using different electron donating groups.Then,utilizing UV-visible absorption,steady-state transient fluorescence emission,single crystal structure and DFT/TDDFT theoretical calculation,etc.,the photophysical properties of them were studied in detail.（1）Aiming at solving the problem that the traditional triplet photosensitizer molecules have weak light absorption in the near infrared region and low light utilization rate,the second chapter of this article selects squaraine dyes with strong absorption in the near infrared region for modification.Four squaraine derivatives（SQ,DISQ,Me SQ,DIMe SQ）with different substitution indole modifications were designed and synthesized.Spectral test results show that in dichloromethane solutions,the molecular SQ,DISQ,Me SQ,and DIMe SQ have absorption wavelengths of 600-700 nm and emission waves of 620-800 nm,all in the near infrared region.In terms of application,the sensitized singlet oxygen properties of four squaraine derivatives were studied.Among them,the molecular DISQ obtained the highest singlet oxygen quantum yield（6%）,which is 2 times that of DIMe SQ（3%）.We speculate that N-hydrogen substituted molecules are more conducive to intersystem crossing than N-methyl substituted molecules.Combined with the single crystal structure and theoretical calculations.Combined with the single crystal structure and theoretical calculations,the intramolecular N-H…O force is conducive to the intersystem transition of molecules,indicating that molecular DISQ can be used as a potential drug for photodynamic therapy.（2）In order to solve the traditional organic triplet photosensitizer molecules mainly rely on the heavy atom effect to promote intersystem crossing.Heavy elements have the disadvantages of being easy to fall off,expensive,and toxic.Therefore,the design of pure organic triplet photosensitizer based on SOCT-ISC mechanism has the advantages of easy synthesis and no heavy atoms.In the third chapter of this article,three squaraine derivatives（SQ-Ph,SQ-AN,SQ-PY）with different aryl substituted triads were synthesized.The triads is mainly to introduce different aryl groups and squaraine dye molecules to form different torsion angles,thereby improving the molecule’s SOCT-ISC.Based on the SOCT-ISC mechanism of squaraine dye,we first proposed it.The photophysical properties of the triads molecules were studied through different spectral tests,density functional theory calculations and single crystal diffraction.The DFT calculation results show that the angles between the phenyl,anthryl,and pyrenyl groups in the molecules SQ-Ph,SQ-AN,and SQ-PY and SQ are38°,79°,and 55°respectively,which is consistent with the single crystal diffraction results.The spectrum test results show that the main absorption wavelength is 550-750 nm,the emission wave is 600-850 nm,all in the near infrared region.And the molecule SQ-AN with an approximately orthogonal structure shows the highest singlet quantum yield（12%）due to the action of SOCT-ISC.At the same time,we studied the effects of different metal ions on the optical properties of molecules SQ,SQ-Ph,SQ-AN,and SQ-PY.The study found that only the molecular SQ-AN showed high selectivity and specificity for metal Co²⁺ions.Surprisingly,after the addition of metal Co²⁺ions,the fluorescence in the molecular SQ-AN solution was clearly quenched,and the singlet oxygen quantum yield doubled（25%）.Through uv-titration,fluorescence titration and nuclear magnetic titration,we can speculate that the molecular SQ-AN and the metal Co²⁺ion are in a 3:2 ratio to form a trimer of the molecular SQ-AN and the metal Co²⁺ion.The formed trimer increases the efficiency of intersystem crossing between molecules,therefore,the singlet oxygen quantum yield of the molecule SQ-AN is improved.Nanosecond transient absorption spectrum test results also confirmed that the addition of metallic Co²⁺ions can indeed significantly enhance the triplet signal of the molecular SQ-AN.The above research will help to design pure organic triplet photosensitizer based on donor/acceptor/donor-system.