Abstract
Two novel thiaheterohelicene derivatives were synthesized from the corresponding 2,2'-(2,6-naphthalenediyl-di-2,1-ethenediyl) bis-thiophene and its dimethyl substituted analogue 2,2'-(2,6-naphthalenediyldi-2,1-ethenediyl) bis-2’’-methylthiophene using oxidative photo cyclization reaction. The compounds were characterized by 1H NMR, electron impact-mass spectrometry, elemental analyses, and the absolute molecular structures were determined by single crystal X-ray diffraction analysis. They crystallized under monoclinic system with space group P21/n for the unsubstituted compound and P21/c for the methyl substituted compound, respectively. The dihedral angle between the terminal thiophene ring and the molecular center was observed to be 20.82? for the unsubstituted compound and 14.27? for the methyl substituted compound, respectively. Furthermore, molecules oriented as herringbone structures by intermolecular π-π stacking in the crystals. The relative study of the actual arrangement of these molecules has been carried out using X-ray diffraction analysis. The two molecules have different crystal packing. The molecule 3b has herring bone like arrangement due to the substituent bulkiness and weak CH-π interaction. On the other hand, the molecular packing of molecule 3a is not herringbone probably due to the multiple weak intermolecular CH-S short contacts between columns consisting of stacked molecules.
Highlights
Helicenes are ortho fused polycyclic aromatic compounds
The compounds were characterized by 1H NMR, electron impact-mass spectrometry, elemental analyses, and the absolute molecular structures were determined by single crystal X-ray diffraction analysis
As part of our continuous interest towards the development of novel polycyclic compounds as semiconductive materials, we report the syntheses of two new thiahelicene derivatives having H (3a) and -CH3 (3b) substituents at α position to the S atom
Summary
Helicenes are ortho fused polycyclic aromatic compounds. The carbohelicenes are more studied, recently heterohelicene molecules having one or more heteroatom have gained great attention due to the extended π-electron conjugation compared with carbohelicene. They have been employed as organic light-emitting diodes [8], organic field effect transistors [9] [10] and photovoltaics [11]. The aim of this research is to study the effect of the -CH3 substitution on the actual arrangement of the molecules using X-ray structural determination of the two molecules. We have taken -CH3 substituent for the comparative study of the effect of substation on the actual arrangement of these molecules because making of this molecule (3b) is easy, economically cheaper compared to the other substituents
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