The ∏-∏ Stacking Interaction And Luminescent Properties Of Organic Cocrystal Materials

The organic cocrystal material has received the attention of people because of its application in many fields, such as pharmaceutics, biology, organic luminescent material, energetic material and so on. Pyrene derivates have often been used in the preparation of organic cocrystal materials. As a result, it has been a research focus that optical or physical and chemical properties of the organic cocrystal materials, including solubility, luminescent property, thermal stability, chemical stability and so on, could be greatly influenced by the π-π stacking interaction between each compound in cocrystal structure. In recent decades, there has been an amount of reports on tuning the properties of drug by cocrystal. However, a few people research its applications in the other fields.Four kinds of pyrene derivates were prepared in this paper, such as pyrene, 1-phenyl-3-(pyren-l-yl)prop-2-en-1-one (C1),1-acetyl-3-phenyl-5-(1-pyrenyl)-pyrazoline (APPP) and 1-acetyl-3-(4-methoxyphenyl)-5-(1-pyrenyl)-pyrazoline (AMPP), prepared cocrystals with different guest compounds at the room temperature, Crystal II (Pyrene:17β-estradiol=1:1), Crystal A (C1:TCNQ=1:1), Crystal B (C1:TCNQ=1:1.5), Crystal C (C1:TCNQ=1:0.5), Crystal D(x) (C1:TCNQ:x=1:1:0.5, x=aromatic solvents), Crystal E (Cl:TCNQ:Methanol= 1:1:1), Crystal M (APPP:TCNQ=2:1), Crystal N (APPP:TCNQ:Acetic acid=1:1:1.5), Crystal X (AMPP:TCNQ=1:1), Crystal Y (AMPP:TCNQ=1.5:1), Crystal Z (AMPP:TCNQ:Acetic acid=1.5:1:2). Single-crystal X-ray diffractometer is used to obtain the structure of these crystals. The space group of Crystal Ⅱ is P212121, The space group of Crystal B, Crystal D(x) and Crystal E are P1, Crystal C is P21/c.The solid fluorescence spectrum for Crystal Ⅱ performs an obvious difference from Crystal I. As a result, the luminescent property could be tuned by changing the π stacking mode in crystal structure. As putting 17β-estradiol molecule insert pyrene crystal structure, a special fence structure consisted of 17β-estradiol has been produced linked by the hydrogen bonds between two adjacent 17β-estradiol molecules, as a result, the n-n stacking interactions between two pyrene molecules in Crystal II are removed, effectively. In addition, Crystal Ⅱ could be obtained by the grinding method, which makes this material more accessible.Experimental results show that solvent effects could be used to explain that Crystal A, Crystal B and Crystal C could be obtained from different solvent regarded of the molar ratio of the starting material, Crystal B induced by acetone, Crystal C by acetonitrile, Crystal A by the mixed solvent of acetone and acetonitrile (1:1 v/v). Similarly, as C1 and TCNQ is dissolved in the mixed solvent with aromatic solvents, methanol and the other solvents, aromatic solvents are packaged in the cocrystal (Crystal D(x)) preferentially, followed by methanol (Crystal E), the other solvents will not be packaged. As a result, three kinds of charge transfer modes consisted of C1 (D) and TCNQ (A) are produced, such as AD AD (Crystal A and Crystal D(x)), AD ADA (Crystal B), ADDADD (Crystal C).In addition, cocrystals linked by charge-transfer interactions will be obtained as APPP or AMPP mixed TCNQ in solution, especially, cocrystal will prefer to package acetic acid molecules to produce the black needle crystal (Crystal N and Crystal Z) as acetic acid molecules are existed in the mixed solvents, otherwise, the binary cocrystals will be obtained, such as Crystal M, Crystal X and Crystal Y, respectively, which are linked by different charge transfer interactions and influenced by solvent effects.