Electronic Circular Dichroism of [16]Helicene With Simplified TD‐DFT: Beyond the Single Structure Approach

Abstract

The electronic circular dichroism (ECD) spectrum of the recently synthesized [16]helicene and a derivative comprising two triisopropylsilyloxy protection groups was computed by means of the very efficient simplified time-dependent density functional theory (sTD-DFT) approach. Different from many previous ECD studies of helicenes, nonequilibrium structure effects were accounted for by computing ECD spectra on "snapshots" obtained from a molecular dynamics (MD) simulation including solvent molecules. The trajectories are based on a molecule specific classical potential as obtained from the recently developed quantum chemically derived force field (QMDFF) scheme. The reduced computational cost in the MD simulation due to the use of the QMDFF (compared to ab-initio MD) as well as the sTD-DFT approach make realistic spectral simulations feasible for these compounds that comprise more than 100 atoms. While the ECD spectra of [16]helicene and its derivative computed vertically on the respective gas phase, equilibrium geometries show noticeable differences, these are "washed" out when nonequilibrium structures are taken into account. The computed spectra with two recommended density functionals (ωB97X and BHLYP) and extended basis sets compare very well with the experimental one. In addition we provide an estimate for the missing absolute intensities of the latter. The approach presented here could also be used in future studies to capture nonequilibrium effects, but also to systematically average ECD spectra over different conformations in more flexible molecules. Chirality 28:365-369, 2016. © 2016 Wiley Periodicals, Inc.

Circularly Polarized Fluorescent Helicene‐Boranils: Synthesis, Photophysical and Chiroptical Properties

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In‐Fjord Substitution in Expanded Helicenes: Effects of the Insert on the Inversion Barrier and Helical Pitch

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A comparison of methods for theoretical photochemistry: Applications, successes and challenges

“…The study finds that CAM-B3LYP and ωB97X-D3 perform best for most excitations, and that in general the RSH functionals perform better than global hybrids. As well as this, a study 157 applying the ωB97X and BHHLYP in conjunction with sTD-DFT to simulate the electronic circular dichroism (ECD) spectra of [16] helicene, finds good agreement with experiment; ECD spectra represent a challenge for TD-DFT as the spectra are sensitive to oscillator intensities.…”