Theoretical Study On The Performance Of Rhenium Complex Containing Ethinyl Ligand As Dye Photosensitizer

With the development of society,the demand for energy and the consumption of traditional fossil energy are increasing day by day,so the search for alternative energy sources has aroused great concern in industry and academia.Solar energy has the advantages of no pollution,abundant resources and so on,which is one of the most promising renewable energy sources.According to statistics,it is predicted that solar energy will dominate in 2050 and is expected to be the main energy source for technological development.Dye-sensitized solar cells（DSSCs）have emerged,which have the advantages of low cost and high energy conversion efficiency,and can be directly converted into electric energy for application.Therein,the dye sensitizers play an important role in improving the photoelectric conversion efficiency of solar cells,so the study of such functional materials has received a lot of attention from the scientific community.In recent years,dye sensitizers based on rhenium and ruthenium complexes have been extensively studied,but their photoelectric conversion efficiencies are still low.Therefore,the development of high-performance dye sensitizers is a hot research topic.The rhenium（Ⅰ）complexes have the advantages of high room temperature phosphorescence quantum yield,relatively short excited state lifetime and high thermal stability.Therefore,structural modification and performance regulation of rhenium（Ⅰ）complexes will be conducive to screening out better dye sensitizers.In the article,based on the experimental synthesis of the parent rhenium（Ⅰ）complex,the properties of the rhenium（Ⅰ）complex were studied by changing the position of the substituents and the position and number of carboxyl ligands.The calculation was carried out using quantum chemical calculation methods,which stating from the microscopic electron configuration of the molecules and considering the solvation effect.The main contents of the discussion are that the properties of the ground state,excited state,the frontier molecular orbitals,absorption spectrum and related theoretical parameters of the molecules,as well as the interface charge transfer characteristics of the interaction between the molecules and TiO₂.The result reveals the relationship between the geometry of the molecules and photoelectric properties and theoretically predicts the performance of rhenium（Ⅰ）complexes.It provided a certain direction for the design and synthesis of new and efficient dye sensitizers.The main contents are as follows:1.A series of complexes were designed by substituting of diimine ligands and phenyl ligands in the parent rhenium（Ⅰ）tricarbonyl diimine complex Re（CO）₃（N^N）[C≡C–C₆H₄–CHC（CN）（COOH）],N^N=1,10-Phenanthroline（phen）（1）with different electron donating groups（-CH₃,-NH₂,-OH）and electron withdrawing groups（-Br,-Cl,-NO₂）.The DFT/TDDFT method was used to study the effects of electronic structures and spectral properties about the isolated dyes and the dyes combined with TiO₂（101）surface.The results show that the geometrical structures of all the design complexes are similar,but the electronic structure is slightly different.The difference in functional groups on the ancillary ligands can significantly affect the energy level of the LUMO,and then affect the molecular orbital energy gap and change the light absorption capacity and photoelectric conversion efficiency of the dyes.Analysis shows that complexes 1,a3,b1,b3,c1 and c3 have smaller energy gap differences,better light-harvesting ability,sufficient driving force and higher charge transfer efficiency,which can be used as appropriate sensitizers.In addition,after the dye molecules combined with the surface of TiO₂（101）,electrons can be directly injected from the dye molecules into the TiO₂ conduction band,which not only reduces the energy gap of the systems,but also have red shifts in the absorption spectrum that guarantee better absorption of sunlight in the visible region.2.The DFT/TDDFT method was used to study the influence of the electronic structures and spectral properties by changing the different number and position of the carboxyl group on the quinoline ligand from the alkynyl-quinolineligand-containing rhenium（Ⅰ）tricarbonyl complex Re（CO）₃（^tBu₂bpy）（HnL）（L=-C≡C-Quin-8-OCOOH）（1）（n=1,a1-a5;n=2,b1-b5）.The study shows that the difference in the number and position of carboxyl groups has a significant effect on the HOMO,which leads to a change in photoelectric conversion capability of the dye molecules.Compared with the parent dye 1,the absorption spectra of all the design complexes are red-shifted,which indicating that they all have good light absorption ability.Based on the comparative analysis of the frontier molecular orbitals,absorption spectra and other parameters,we conclude that the complexes 1,a2 and b2 can be used as better dye sensitizers,and the carboxyl sites have a greater influence on the performance of dyes.