The bisazomethine dyes derived from diaminomaleonitrile and aminobenzaldehydes, 2,3-bis[(E)-4-(dialkylamino)benzylideneamino]fumaronitrile derivatives, are known to have potential as dyes for forming J-aggregate vapour-deposited films, even though appropriate conditions for preparation of their pure J-aggregate films are unknown. In this study, an attempt was made to investigate the effects of alkoxy substitution on the crystal structures of eight bisazomethine dyes; our final goal was to obtain pure J-aggregates of bisazomethine dyes in a crystalline state. The focus of this study is on the relationship between changes in the molecular structure and the crystal structure, characterized by a two-dimensional molecular stacking layer and its alignment. We found that the interlayer distance between adjacent two-dimensional stacking layers can be controlled by alkoxy substitution, when the substituent chain length is less than C10, without any significant structural changes in the stacking layer. Our observation was confirmed by lattice energy calculations from an energetic perspective. Scheme 1 Chemical structures of dyes 1-8.
Here, we report the J-aggregate structure of a chloroform solvate of 5-t-butyl-2,3-dicyano-6-[4-(dimethylamino)styryl]-pyrazine with a strong intramolecular charge transfer system. The dye was found to form a two-dimensional brick-wall structure separated by chloroform molecules in the solvated crystals, which exhibited intense red fluorescence. The absorption maximum of the solvate was also found to show a bathochromic spectral shift. These observed optical characteristics were interpreted in terms of excitonic intermolecular interaction based on two-dimensional brick-wall structure which is one of the proposed structures for J-aggregates.
Opticalproperties of three crystal modifications of 5-t-butyl-2,3-dicyano-6-[4-(dimethylamino)styryl]-pyrazine having different color appearances were measured and interpreted on the basis of a crystal structure analysis. Two of the three modifications exhibited a bathochromic spectral shift both in absorption and fluorescence compared with those in a toluene solution of the dye. The crystal structure analysis revealed that a
Some pyrazine dyes are known to display strong fluorescence not only in solution but also in the solid-state. 5-t-Butyl-2,3-dicyano-6-[4-(dimethylamino)styryl]pyrazine (1) is a 2,3-dicyanopyrazine dye synthesized for an examination of substituent effects on thin-film growth [1]. Dye 1 was found to exhibit three crystal modifications with different color appearance (I: red, II: black, III: reddish purple). Modification I is a solvate crystal including one chloroform per one dye molecule [2], and modifications II and III are polymorphs. In this work, optical properties of these three modifications were interpreted on the basis of their crystal structures. The absorption spectra of the modifications were measured using optical waveguide spectroscopy. The absorption maxima of modifications I, II and III were found at 559 nm, 462 nm and 571 nm, respectively. A bathochromic absorption shift of reddish modifications I and III from that of 1 in toluene was 79 nm (-2944 cm-1) and 91 nm (-3320 cm-1), respectively. On the other hand, a hypsochromic absorption shift of 18 nm (812 cm-1) was observed in modification II. The fluorescence maxima of modifications I, II and III were found at 619 nm, 734 nm and 668 nm, respectively. The energy displacement corresponding to the observed spectral shifts was characterized in terms of an exciton interaction. The exciton interaction for a dimer was estimated using the extended dipole model, and the nearest-neighbor approximation was applied for evaluating a total energy displacement due to crystallization. The calculation results were qualitatively in good agreement with the observed spectral shifts. The result also revealed that molecular pairs in two-dimensional stacking structure in these modifications play a significant role in the total energy displacement.
Malaria is an infectious disease caused by the parasite Plasmodium falciparum invading red blood cells. Toxic free heme released by the parasitic destruction of hemoglobin is detoxified by conversion to malaria pigment. The µ-oxo TPP and OEP heme complexes have been studied as malaria pigment model systems [1]. The current study focuses on structure correlation of these and [Fe(PPIX)] 2 (µ-O) in an effort to better understand the relationship between the spectra of malaria pigment and the µ-oxo heme complexes. The supramolecular interactions between propionate chains, C−H•••O and interplanar interactions, C−H•••π in [Fe(PPIX*)] 2 (µ-O) are observed. The tight H•••O interaction distances are 2.62(4) Å while the H•••π distances are 2.84(5)-2.93(5) Å.
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