78487-00-0Relevant academic research and scientific papers
Ortho-Phenylene oligomers with terminal push-pull substitution
He, Jian,Mathew, Sanyo M.,Cornett, Sarah D.,Grundy, Stephan C.,Hartley, C. Scott
experimental part, p. 3398 - 3405 (2012/05/31)
ortho-Phenylenes are an emerging class of helical oligomers and polymers. We have synthesized a series of push-pull-substituted o-phenylene oligomers (dimethylamino/nitro) up to the octamer. Conformational analysis of the hexamer using a combination of low-temperature NMR spectroscopy and ab initio predictions of 1H NMR chemical shifts indicates that, like other o-phenylenes, they exist as compact helices in solution. However, the substituents are found to have a significant effect on their conformational behavior: the nitro-functionalized terminus is 3-fold more likely to twist out of the helix. Protonation of the dimethylamino group favors the helical conformer. UV/vis spectroscopy indicates that the direct charge-transfer interaction between the push-pull substituents attenuates quickly compared to other conjugated systems, with no significant charge-transfer band for oligomers longer than the trimer. On protonation of the dimethylamino group, significant bathochromic shifts with increasing oligomer length are observed: the effective conjugation length is 9 repeat units, more than twice that of the parent oligomer. This behavior may be rationalized through examination of the frontier molecular orbitals of these compounds, which exhibit greater delocalization after protonation, as shown by DFT calculations.
Syntheses and Spectral Characteristics of Seven Polyphenyls Containing Highly Branched para-Phenylene Ring(s)
Fujioka, Yasuhiro,Ozasa, Shigeru,Sato, Kazumi,Ibuki, Eiichi
, p. 22 - 29 (2007/10/02)
Seven polyphenyls, including four new compounds, 2,2',6'- (2) and 3,2',6'-triphenyl-p-terphenyl (3), 3',5'-diphenyl-p-quarterphenyl (4), and 2-phenyl-3'-(2-biphenylyl)-p-terphenyl (7), were synthesized by the Ullmann coupling reaction of aryl iodide(s) or by the Kharash type coupling reaction of aryl Grignard reagent with an aryl iodide catalyzed by bis(acetylacetonato)-nickel(II).Infrared spectral studies of the polyphenyls showed that the range of 730-770 cm-1, generally accepted as the position of the out-of-plane C-H bending bands of the phenyl ring, should be widened slightly to 730-786 cm-1.The high frequency bands were confirmed to be correlated closely to the overcrowding by terminal rings in the complex structures.Proton magnetic resonance spectral studies indicated that he characteristic spectral features of the branched polyphenyls were consistent with their conformational aspects deduced from stereomodels.In the ultraviolet spetcral studies the polyphenyls containing highly branched p-phenylene ring(s) showed intense K-bands or shoulders at locations very similar to those of the corresponding linear polyphenyls containing the same number of p-phenylene rings. Keywords -- Ullmannn reaction; Ni-complex-catalyzed cross-coupling; quinquephenyl; sexiphenyl; octiphenyl; IR; UV; 1H-NMR
