ИСТИНА

The production of cocrystals of organic molecules is a direction in crystal engineering which has recently attracted a lot of interest in connection with the development of new functional materials with unusual optoelectronic properties. On the one hand, design of cocrystals opens the prospect of a purposeful change in the packing of molecule responsible for certain property in order to tune this property. This is possible thanks to a large number of organic molecules which can form cocrystals with the key molecule. On the other hand, design of cocrystals opens the possibility to combine several properties from different molecules in one crystal simultaneously. However in cocrystals of organic luminophores there is a problem of the total energy transfer from a component that emits in short-wavelength region to a component that emits in long-wavelength region. This caused several unsuccessful attempts to make crystals of salts comprised by cation and anion, which possess complementary emission[1,2]. Nevertheless there is one example of salt in which both centres luminesce – this is a mixed salt of new organic anion 3-cyano-4-dicyanomethylene-5-oxo-4,5-dihydro-1H-pyrrole-2-olate (HA-), its deprotonated form (A2-) and cadmium cation Cd2+: [Cd3(HA)2(A)2(H2O)10]·0.5H2O [3]. In crystals of this salt dianion A2- emits in short-wavelength region (377 nm), anion HA- emits in long-wavelength region (620 nm). Therefore it is possible to design crystals of organic salt, in which one ion emits in short-wavelength region and the other emits in long-wavelength region (ideally in two complementary spectral regions). One needs only to define a specific packing of ions in crystal necessary for this. Salt built of anion HA- and cation 2-aminopyridinium (APY+) has been chosen to solve this problem. Fluorescence spectrum maximum of HA- in crystal lies in range of 544-669 nm depending on its molecular surroundings [4]. Fluorescence spectrum maximum of APY+ lies near 367 nm [5]. The salt was synthesized, three types of crystals with composition APY+HA-, APY+HA-·H2O(α,β) were obtained and their crystal structures were determined using single crystal x-ray diffraction, their fluorescent spectra were recorded. It turned out that in all types of crystals fluorescence of cation APY+ was absent. Water solution of this salt as well as filter paper saturated with this salt gave clear peak of cation fluorescence. For three types of crystals wavelength of fluorescence spectrum maximum of HA- is correlated with crystal structure. Attempt to disclose an effect of substrate on cation fluorescence in APY+HA- salt is made. [1] Wu C., Chen H.-F., Wong K.-T., Thompson M.E. J. Am. Chem. Soc. 2010, 132, 3133-3139. [2] Sandroni M., Zysman-Colman E. Dalton Trans. 2014, 43, 3676-3680. [3] Tafeenko V.A., Panin G.N., Baranov A.N., Bardasov I.N., Aslanov L.A. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 2007, 63, m541-m547. [4] Tafeenko V.A., Gurskiy S.I. Cryst. Growth Des. 2016, 16, 940-945. [5] Rusakowicz R., Testa A.C. J. Phys. Chem. 1968, 72, 2680-2681.