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Issue 48, 2017
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The shape of the electronic circular dichroism spectrum of (2,6-dimethylphenyl)(phenyl)methanol: interplay between conformational equilibria and vibronic effects

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Abstract

Comparison between chiroptical spectra and theoretical predictions is the method of choice for the assignment of the absolute configuration of chiral compounds in solution. Here we report the case of an apparently simple biarylcarbinol, whose electronic circular dichroism (ECD) in the 1Lb region exhibits a peculiar alternation of negative and positive bands. Adopting Density Functional Theory, and describing solvent effects with implicit methods, we found three stable conformers in ethanol, each of them with two close lying states corresponding to similar local 1Lb excitations on the two phenyls. We computed the corresponding vibronic ECD spectra in harmonic approximation, including Duschinsky mixings as well as both Franck Condon (FC) and Herzberg Teller (HT) effects. Exploiting a recently developed mixed quantum/classical method, we further investigated the contribution of the vibronic spectra of out-of-equilibrium structures along the interconversion path connecting the different conformers. In this way, we achieved a reasonable agreement with experiment and attributed the alternating signs of the bands to the existence of different conformers. The remaining discrepancies with experiment indicate that specific solute–solvent interactions modulate the relative conformers’ stabilities, calling for new methods able to combine Molecular Dynamics explorations and vibronic calculations. Moreover, the poor performance of HT approaches and the existence of two closely-lying states suggest the necessity of an improved fully-nonadiabatic vibronic approach. These findings demonstrate that even for such a simple system as the biarylcarbinol investigated here, a full reproduction of the fine details of the ECD spectrum requires the development of new improved methods.

Graphical abstract: The shape of the electronic circular dichroism spectrum of (2,6-dimethylphenyl)(phenyl)methanol: interplay between conformational equilibria and vibronic effects

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Publication details

The article was received on 17 Sep 2017, accepted on 16 Nov 2017 and first published on 16 Nov 2017


Article type: Paper
DOI: 10.1039/C7CP06369E
Citation: Phys. Chem. Chem. Phys., 2017,19, 32349-32360
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    The shape of the electronic circular dichroism spectrum of (2,6-dimethylphenyl)(phenyl)methanol: interplay between conformational equilibria and vibronic effects

    D. Padula, J. Cerezo, G. Pescitelli and F. Santoro, Phys. Chem. Chem. Phys., 2017, 19, 32349
    DOI: 10.1039/C7CP06369E

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