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J Phys Chem A. 2012 Aug 30;116(34):8744-52. doi: 10.1021/jp304997b. Epub 2012 Aug 16.

Obtaining enhanced circular dichroism in [4]heterohelicenium analogues.

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  • 1Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen, Denmark.


Electronic circular dichroism in the three helicenium analogues dimethoxyquinacridinium (DMQA(+)), dimethoxychromenoacridinium (DMCA(+)), and dimethoxychromenoxanthenium (DMCX(+)) were investigated in vacuum with time-dependent density functional theory methods using the CAM-B3LYP functional with the basis set 6-311++G**. The systems were thoroughly studied by designing derivatives with several different electron-donating and -withdrawing substituents while at the same time keeping the net charge of the molecule either positive, neutral, or negative. Fifty-six derivatives were examined, and we identify a superior substitution pattern that is found to be independent of the bridging atoms and gives a rotational strength close to 90 × 10(-40) esu(2) cm(2) for DMQA, DMCA, and DMCX. The optimal system shows promising applications as a chromophore because it has a highly allowed primary electronic transition with an angle between the electronic and magnetic transition dipole moments close to 50° and its chiroptical response is thereby limited only by the magnetic transition.

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