Hong, SY Kim, DY Kim, CY Hoffmann, R 2024-01-21T12:05:14Z 2024-01-21T12:05:14Z 2021-09-04 2001-08 0024-9297 https://pubs.kist.re.kr/handle/201004/140296 A quantum-chemical study of conformations and electronic structures of poly(m-phenylene) [PMP] and the related polyphenylenes was performed to elucidate the origin of the broken conjugation found in m-phenylene linked conjugated polymers. Potential energy curves of the polymers as a function of both torsion and helical angles were constructed through semiempirical Hartree-Fock band calculations at the Austin model I (AM1) level. It is found that two helical conformations of PMP are possible: one with a helical angle (alpha) of 72 degrees and the other with alpha = 144 degrees. The former is identical with the conformation of an oligomer in the solid state, m-deciphenyl structure. Our calculations predict that both helices are more stable by 2.5 kcal/mol per phenyl ring than the anti-coplanar conformation and that they exhibit absorption peaks at 5.8 eV. The electronic structure of PMP is, however, not affected significantly by increasing the planarity of a PMP chain but affected by copolymerization with other conjugated units. This implies that localization occurs in the m-phenylene ring itself. We examined the electronic structures of PMP and the related copolymers and found that the weak conjugation along the m-phenylene linked conjugated backbone is related to the inherent nodal nature of the frontier molecular orbitals of the unit even in the planar conformation. English AMER CHEMICAL SOC Origin of the broken conjugation in m-phenylene linked conjugated polymers Article 10.1021/ma010254k 1 MACROMOLECULES, v.34, no.18, pp.6474 - 6481 MACROMOLECULES 34 18 6474 6481 N scie scopus 000170662100050 2-s2.0-0035964514 Polymer Science Polymer Science Article STRUCTURAL PHASE-TRANSITION LIGHT-EMITTING-DIODES CRYSTAL-STRUCTURE ELECTRONIC-STRUCTURES FIRST-PRINCIPLES AB-INITIO POLY(PARA-PHENYLENE VINYLENE) ELECTROLUMINESCENT POLYMERS ELECTROCHEMICAL PROPERTIES POLYFLUORENE DERIVATIVES conjugated polymer