[materials] photosensitive core-shell liquid crystal structure based on PBI

Perylene bisimides (PBIS) are a series of planar or twisted structures obtained by introducing different groups at the position of imide and "island" from perylene anhydride Because the framework of perylene bisimides is planar perylene anhydrides, PBIS generally retain good optical and thermodynamic stability of perylene anhydrides Not only that, PBIS have many other advantages, such as good dispersion, photoelectric stability and so on These characteristics make PBIS widely used in LED, airport effect, solar cell, molecular switch, liquid crystal display and other fields Figure 1 The structure of PBI derivatives and the schematic diagram of their columnar helical structure (picture source: angelw Chem Int ed.) recently, Professor Matthias Lehmann and Professor Frank w ü rthner from the University of ulzburg, Germany, jointly reported a perylene imide derivative (PBI 2t), generally speaking, due to PBIS The central structure of PBIS perylene anhydrides with planar structure, so it can form one-dimensional H-type aggregate through π - π stacking, which greatly limits the application of PBIS in the field of optoelectronics To solve this problem, our team designed this perylene diimide derivative with a special substituent group They introduced 3,4 in the bay of perylene anhydride, 5-tris (dodecyl) phenyl dithiophene group (Fig 1a), in this way, changes the aggregation behavior of perylene diimide, resulting in the formation of a columnar spiral structure, and the aggregates of perylene anhydride and dithiophene in the material are J-type and H-type respectively This achievement was published in German Applied Chemistry (DOI: 10.1002 / anie 201904789) under the title of "photoconductive core – shell liquid ‐ crystal of perylene bisimide J ‐ aggregate donor ‐ acceptor dyad" Fig 2 The synthesis route of pbi2t (picture source: angel Chem Int ed.) the synthesis of pbi2t is not complicated Firstly, the 3,4,5-tris (dodecyl) phenylthiophene containing methyl ester is obtained by one-step Suzuki coupling reaction between the brominated thiophene derivative (Fig 2,1) and 2 Then, the 3 containing carboxylic acid group is obtained by demethylation, 4,5-tris (dodecyl) phenyl dithiophene (Fig 2,4) and 1,6,7,12-tetrahydroxyphenoxy perylene-3,4,9, The final PBI product (pbi2t, Fig 2) can be obtained by the reaction of 10 tetramethyldiimide (Fig 2, 5) Different from the general PBIS, the author did not introduce substituent at the position of amide, which was explained by the author to increase the hydrogen bond in the structure as much as possible Fig 3 UV absorption spectrum (a), microstructure (b) and photocurrent measurement diagram (c) (picture source: angelw Chem Int ed.) after obtaining the material, the author first studied its spectral properties The results show that pbi2t monomers in the solution have obvious UV absorption at 385 nm and 569 nm (Fig 3a), which correspond to the UV absorption of thiophene group and perylene anhydride monomers respectively After they are made into films (the materials aggregate), the absorption at 385 nm decreases significantly, while the absorption at 569 nm moves to 653 nm, which shows that pbi2t After the formation of aggregates, the aggregation behavior of the two parts is not the same, in which J-type aggregation occurs in perylene anhydride, while H-type aggregation occurs in thiophene group However, it is interesting that the fluorescence emission of PBI can be observed by either the excitation wavelength of PBI or the excitation wavelength of thiophene, which indicates that there is an electron transfer effect (PET) between PBI and thiophene In addition, by polarizing optical microscopy (POM) and differential scanning calorimetry (DSC), it is found that pbi2t exhibits the characteristics of liquid crystal from 20 ℃ to 281 ℃, and at this temperature, the material will start to melt and decompose The structure of the material in liquid crystal state has been studied by WAXS and maxs The results show that the material is a helical columnar structure (Fig 3b) The author speculates that the self-assembly with this structure may improve the transfer efficiency of excitons in the long-distance transport, so it is expected to become a photosensitive element The experimental results confirm the author's conjecture that the photocurrent of the material is only a few hundred FIA in the dark room condition, and the photocurrent of the material can exceed 1 Na in the light condition (Fig 3C) Full text author: Markus Hecht, Tim schlossarek, Matthias stolte, Matthias Lehmann and frank w ü rthner.