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Issue 38, 2017
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Optical and magnetic properties of antiaromatic porphyrinoids

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Abstract

Magnetic and spectroscopic properties of a number of formally antiaromatic carbaporphyrins, carbathiaporphyrins and isophlorins with 4n π electrons have been investigated at density functional theory and ab initio levels of theory. The calculations show that the paratropic contribution to the magnetically induced ring-current strength susceptibility and the magnetic dipole-transition moment between the ground and the lowest excited state are related. The vertical excitation energy (VEE) of the first excited state decreases with increasing ring-current strength susceptibility, whereas the VEE of the studied higher-lying excited states are almost independent of the size of the ring-current strength susceptibility. Strong antiaromatic porphyrinoids, based on the magnitude of the paratropic ring-current strength susceptibility, have small energy gaps between the highest occupied and lowest unoccupied molecular orbitals and a small VEE of the first excited state. The calculations show that only the lowest S0 → S1 transition contributes signficantly to the magnetically induced ring-current strength susceptibility of the antiaromatic porphyrinoids. The decreasing optical gap combined with a large angular momentum contribution to the magnetic transition moment from the first excited state explains why molecules III–VII are antiaromatic with very strong paratropic ring-current strength susceptibilities. The S0 → S1 transition is a magnetic dipole-allowed electronic transition that is typical for antiaromatic porphyrinoids with 4n π electrons.

Graphical abstract: Optical and magnetic properties of antiaromatic porphyrinoids

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Publication details

The article was received on 14 Aug 2017, accepted on 11 Sep 2017 and first published on 18 Sep 2017


Article type: Paper
DOI: 10.1039/C7CP05460B
Phys. Chem. Chem. Phys., 2017,19, 25979-25988

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    Optical and magnetic properties of antiaromatic porphyrinoids

    R. R. Valiev, H. Fliegl and D. Sundholm, Phys. Chem. Chem. Phys., 2017, 19, 25979
    DOI: 10.1039/C7CP05460B

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