Synthesis And Properties Of Multi-branch Phenothiazine Dyes Based On Alkyne Bond

Since the beginning of the 21st century,human demand for energy is increasing day by day,and people’s large-scale use of fossil energy such as crude oil and coal also brings environmental problems.Therefore,people have conducted a lot of research on green and renewable energy,including sunlight,in order to solve the environmental problems which plague the world today,such as greenhouse gases.However,the development of solar cell is still affected by the low efficiency of photoelectric conversion and the poor battery stability.While working on solar cells,scientists have discovered a new form of cell for studying photosynthesis in plants,called dye-sensitized solar cells（DSSC）..Dyes as a key factor affecting the photoelectric performance of DSSC,is mainly used to convert free electrons exciting state electrons absorbing photons from sunlight,which enter into the titanium dioxide conduction band and convert into electric energy,and then the electrons return to the battery system through the electrolyte.Based on the previous work of the research group,the synthesis and properties of several multi-chain phenothiazine dyes based on acetylene bridge were studied in this paper,which are mainly divided into the following contents:（1）Synthesis and properties of FCDD and FCTD series dyesUsing 2-bromofluorene and phenothiazine as starting materials,fluorene unit-containing phenothiazine single-chain derivatives were synthesized through multi-step reactions.Then using single-chain precursors and polyiodides as starting materials,a series of alkyne-linked phenothiazine multi-chain dyes（namely FCDD-1,FCDD-2,FCDD-4,FCTD-1）were synthesized through multi-step reactions.The structures of the obtained unknown compounds were characterized by NMR and MS.The FCDD series are typically double-stranded（D-π-A）₂structural dyes.In this paper,some methods were used to expand the light absorption range of dyes,enhance the light absorption capacity of dyes,and inhibit the charge recombination of electrons on solar cells,prevent dye aggregation,so as to improve the performance of solar cells.The FCTD series are novel（D-π-A）₃structural dyes with three-unit chains based on conjugated bridging,increasing the number of unit chains on the benzene ring,expanding the light absorption range of the dye,enhanceing the light absorption ability of the dye,and improve the photoelectric properties of the dye.In addition,in order to reduce the aggregation effect of dyes,the alkyl chain of dyes was extended,and fluorene derivatives were introduced as electron-donor groups to increase the electron-donor capacity of dyes.Finally,as a conjugate structure,benzene ring was used to connect the precursor unit chain of dyes to broaden the conjugated system of dyes and enhance the light absorption and light capture capacity of dyes.This study is expected to attract more researchers to explore dyes with multi-chain D-π-A structures and accelerate the creation of new high-performance dyes.（2）Electrochemical properties of DSSC based on FCDD and FCTD series dyesThe photoelectric properties of the dyes were studied by means of UV-Vis spectroscopy and photocurrent working spectrum of DSSC.The performance of para-position double-chain dyes on benzene ring was better than that of interposition double-chain dyes,and the double-chain dyes with thiophene as the bridging bridge exhibited the best photoelectric performance.Besides,compared with double chain dyes,triple chain dyes showed better photoelectric parameters such as open circuit voltage and short circuit current density,indicating that the improvement of photoelectric conversion efficiency of DSSC could also rely on wider conjugated structure.Three-chain dye FCTD-1 sensitized solar cells exhibited the most excellent performance,under the simulated sunlight（AM1.5,100 m W/cm²）,the open circuit voltage was 0.79 V,the short-circuit current density was 6.77 m A/cm²,the filling factor was 0.74 and the total photoelectric efficiency could reach 4.0%.It was found that both FCDD and FCTD series dyes have good performance when they form solar cells.