Steric and Electronic Effects in Methyl-Substituted 2,2'-Bipyrroles and Poly(2,2'-Bipyrrole)s: Part II. Theoretical Investigation on Monomers
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- 作者：Carlo Gatti ; Giovanni Frigerio ; Tiziana Benincori ; Elisabetta Brenna ; Franco Sannicolò ; Gianni Zotti ; Sandro Zecchin ; and Gilberto Schiavon
- 刊名：Chemistry of Materials
- 出版年：2000
- 出版时间：May 2000
- 年：2000
- 卷：12
- 期：5
- 页码：1490 - 1499
- 全文大小：184K
- 年卷期：v.12,no.5(May 2000)
- ISSN：1520-5002
文摘
The effects of N- and C
-methyl substitution in pyrrole and 2,2'-bipyrrole were investigatedthrough ab initio calculations and Atoms in Molecules analysis of the resulting wavefunctions. Replacement of a hydrogen atom with a methyl group in pyrroles lowers theionization potential, with substitution at C3 being more efficient than N-substitution becauseof the larger release of 
population to the ring in the former case. Full geometry optimizationat RHF/6-31G** level and as a function of the torsion angle 
between two adjacent ringsdemonstrates that the increasing loss of planarity in the 2,2'-bipyrrole, N,N'-dimethyl-2,2'-bipyrrole, and 3,3'-dimethyl-2,2'-bipyrrole series, adversely affects the positive contributionsexpected from methyl substitution. An intramolecular interaction energy model shows thatthe greater anti-planarization energy of N,N'-dimethyl-2,2'-bipyrrole, as compared to 3,3'-dimethyl-2,2'-bipyrrole, is due to the larger decrease in the stabilizing electrostatic termand to the larger increase in the destabilizing nonbonding contribution which occurs at =0
in the former. Calculations on the corresponding monocations and analysis of newconductivity measures on substituted poly(2,2'-bipyrrole)s suggest that the ease in achievinglocal chain planarity in doped polypyrroles should be more closely correlated to the anti-planarization energies of the charged monomers rather than to anti-planarization energiesof the neutral monomers.
-methyl substitution in pyrrole and 2,2'-bipyrrole were investigatedthrough ab initio calculations and Atoms in Molecules analysis of the resulting wavefunctions. Replacement of a hydrogen atom with a methyl group in pyrroles lowers theionization potential, with substitution at C3 being more efficient than N-substitution becauseof the larger release of population to the ring in the former case. Full geometry optimizationat RHF/6-31G** level and as a function of the torsion angle between two adjacent ringsdemonstrates that the increasing loss of planarity in the 2,2'-bipyrrole, N,N'-dimethyl-2,2'-bipyrrole, and 3,3'-dimethyl-2,2'-bipyrrole series, adversely affects the positive contributionsexpected from methyl substitution. An intramolecular interaction energy model shows thatthe greater anti-planarization energy of N,N'-dimethyl-2,2'-bipyrrole, as compared to 3,3'-dimethyl-2,2'-bipyrrole, is due to the larger decrease in the stabilizing electrostatic termand to the larger increase in the destabilizing nonbonding contribution which occurs at =0 in the former. Calculations on the corresponding monocations and analysis of newconductivity measures on substituted poly(2,2'-bipyrrole)s suggest that the ease in achievinglocal chain planarity in doped polypyrroles should be more closely correlated to the anti-planarization energies of the charged monomers rather than to anti-planarization energiesof the neutral monomers.