| Singlet exciton fission（SF）is a spin-allowed multi-exciton generation process,in which one high-energy singlet exciton is transformed into two or more low-energy triplet excitons.With multi-exciton generation capability,SF is believed to have potential to break the 33%of Shockley-Quiesser limit by overcoming thermalization losses in third-generation solar cell devices.However,the practical applications of SF materials are greatly hindered by the limited availability of suitable materials.The triplet pairs generated by intramolecular singlet fission decay rapidly and dissociate difficultly,which is not conducive to their application in SF photovoltaic devices.In response to the above problems,it is necessary to understand the interaction between the intramolecular singlet fission materials and the intramolecular singlet fission mechanism,develop new singlet fission material and understand the effect of heteroatom modification for the excited state dynamic.In this paper,a series of acene derivatives were designed and synthesized,and the effects of solvent environment and bridging units of isomers on intramolecular singlet fission were systematically studied by ultrafast spectroscopy;a new stable singlet fission material was developed;the effect of sulfur atom on the excited state dynamics of perylene diimide was studied.The specific research contents are as follows:1.We designed and synthesized a phenothiazine-bridged pentacene dimer PPTZP,and studied the effect of solvent environment on the intramolecular singlet fission.Adding an oxidizing acid to the solution of PPTZP makes PPTZP become PPTZP+·,which bridge by the phenothiazine radical cation.The transient absorption spectra does not detect the triplet excitons signal in PPTZP+·,indicating that there is no singlet fission.Theoretical calculations suggest that it may be due to the interaction between the pentacene and the bridging unit.We further studied the effects of n-hexane,toluene and chloroform on the singlet fission of PPTZP.2.We designed and synthesized pentacene dimer molecules 13PAP,26PAP and PNP,which linked by azulene and naphthalene as bridging units,and studied the effect of bridging units with dipoles on intramolecular singlet fission.Previous studies have shown that the choice of bridging unit for singlet splitting has a significant effect.Herein,transient absorption spectra show that singlet fission is not observed in neither13PAP nor 26PAP,but fast and efficient singlet fission occurs in PNP.Theoretical calculations show that the electron clouds of LUMO or HOMO in 13PAP and 26PAP are also distributed in the bridging unit,indicating that pentacene interacts with the bridging unit,which is not conducive to the occurrence of singlet fission.3.We developed a new stable and efficient singlet fission material and investigated the effect of stacking on singlet fission.These N-doped two-dimensional angular fused acenes have three sets of aromatic Clar sextets,making them significantly more stable than linear acenes with only one sextet.Time-resolved spectroscopy characterization reveals that the SF process occurs in the polycrystalline films of EH-Fla and TIPS-Fla,with maximal triplet yields of 32%and 159%,respectively.The SF processes of these two molecules are mediated by excimer states.In EH-Fla,the low-lying excimer prevents the SF process to occur effectively,resulting in a low triplet yield.In contrast,the excimer state in TIPS-Fla is mixed with strong CT coupling,which prompts the efficient SF and results in a high triplet yield.4.We designed and synthesized the perylene diimide derivatives PDI,SPDI,2SPDI,3SPDI and 4SPDI with different numbers of sulfur atoms,and studied the effect of sulfur atoms on the excited state kinetics and nonlinear optical properties.The excited state kinetics of this series of molecules in solution were studied by transient absorption spectroscopy.Combined with transient absorption spectroscopy,the properties and mechanism of nonlinear optics were studied by nanosecond Z-scan technique. |
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