Large molecular hyperpolarizabilities in "push-pull" porphyrins. Molecular planarity and auxiliary donor-acceptor effects

被引:115
作者
Albert, IDL
Marks, TJ
Ratner, MA
机构
[1] Northwestern Univ, Dept Chem, Evanston, IL 60208 USA
[2] Northwestern Univ, Mat Res Ctr, Evanston, IL 60208 USA
关键词
D O I
10.1021/cm970478a
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
Linear optical and SHG coefficients of a number of "push-pull" porphyrins are analyzed using the semiempirical INDO/S Hamiltonian and singles-only CI. The NLO response properties are computed at a nonresonant excitation energy of 0.1 eV using the correction vector formalism, and the calculations are carried out in both ideal planar and SYBYL force-field optimized geometries. The results strongly suggest that large NLO responses may be obtained by (1) minimizing the dihedral twist of phenyl substituents with respect to the porphyrin plane, (2) replacing the homoaromatic phenyl rings in tetraphenylporphyrins by electron excessive or deficient heteroaromatic rings such as pyrrole or tetrazine, (3) exploiting the electron-excessive and -deficient sites of the porphyrin pi-electron bridge itself. Thus, functionalizing the electron excessive beta position with donor substituents and electron-deficient meso position with acceptor substituents leads to enhanced NLO response properties. The enhancement in the NLO response properties is modest in chromophores containing spacer groups which reduce the dihedral twist angles. This is attributed to the diminished inductive effect of the electron excessivity/deficiency of the porphyrin rings due to the intervening spacer and phenyl moieties.
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页码:753 / 762
页数:10
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