Synthesis And Charge-Transfer Properties Of Hybrid Main-Group Metal Halides With Pyridyl-TTF Derivatives

There are various electronic states of tetrathiofulvalene(TTF)and its derivatives including neutral or radical cations,which endows TTF with adjustable electrochemical and optical properties.In most reported TTF-metal halides,TTF exists in the form of oxidation.It has been found that neutral TTF can be used as a hole transport material in perovskite solar cells and exhibit good photoelectric conversion efficiency.Therefore,it is important to introduce neutral TTF into the metal halide system to study the charge transfer properties between neutral TTF and metal halides at the molecular level.In this paper,methylated bipyridine or protonated bipyridine were introduced into TTF system to obtain positively charged TTF derivatives,but the oxidation state of TTF itself was still neutral.Then it was combined with negatively charged bismuth and lead halides to study the charge transfer between TTF derivatives and bismuth and lead halides,and to explore their effects on photoelectric properties.This paper mainly includes the following aspects:In the introduction,the properties and latest research progress of TTF and its derivatives are summarized.Charge transfer complexes containing TTF,organic-inorganic hybrid materials and their applications and properties in battery energy are introduced.At the same time,the development of organic-inorganic lead and bismuth halides is briefly summarized.Finally,this paper elaborates the topic selection ideas and research content.In the second section,four novel TTF-bimuth halides were obtained using dimethylated and diprotonated bis(4'-pyridyl)-tetrathiafulvalene divalent cations(denoted as(MePy)2TTF and(HPy)2TTF)and bismuth halides:[(MePy)2TTF]3[Bi2l9]2-4DMF(1),[(HPy)2TTF]3[Bi2I9]2·8DMF(2),[(MePy)2TTF][BiBr5DMF]·DMF(3),and[(MePy)2TTF][BiCl5DMF]·DMF(4).Single crystal analysis showed that the TTF cations regularly stack to form an extend infinitely column.Bismuth-halide anions were embedded between TTF columns through anion-cation interaction.Among these compounds,the main contribution of charge transfer(CT)is intramolecular CT(IMCT)from TTF molecules to pyridyl groups.However,charge transfer between anions and cations(ACCT)has a significant effect on the physical properties of IMCT and compounds.Different interaction modes of anions and cations lead to different synergistic effects between IMCT and ACCT,which changes the band gap and photocurrent properties of the compounds.This study gives a clear relationship between structure and properties,hoping to be helpful for the design of new perovskite materials at the molecular level.In the third section,compound[(MePy)2TTF][Pb2I6]·DMF(5)was obtained using(MePy)2TTF and lead-iodide.The single crystal X-ray diffraction(XRD)results show that the Pb-I halide has a one-dimensional chain structure.Elemental analysis further confirmed the composition of the molecular formula.The solid-state optical diffuse reflectance spectroscopy,electron spin resonance(ESR)and cyclic voltammetry(CV)measurements of compound 5 showed that charge transfer occurs between cation TTF and Pb-I anion.The photocurrent response measurement shows that the photoelectric response of compound 5 is stronger than that of the starting material and it can maintain stability for a long time.Fourthly,the overall work is summarized,and new breakthroughs in TTF-perovskite research are expected in the future.