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Electronic absorption, polarised excitation, and circular dichroism spectra of [5]-helicene (dibenzo[c,g]phenanthrene)
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1971
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EngineeringGeneral Helix ModelParent HydrocarbonOrganic ChemistryComputational ChemistryCircular Dichroism SpectraChemistrySpectra-structure Correlationπ–Scf ApproximationMolecular SpectroscopyBiophysicsPhysicsPhysical ChemistryElectronic AbsorptionQuantum ChemistryMolecular ChemistrySupramolecular ChemistryMolecular ModelingOrganic Charge-transfer CompoundNatural SciencesMolecule-based Material
The absorption and circular dichroism spectra of (+)-dibenzo[c,g]phenanthrene-9,10-dicarboxylic acid are reported, together with the polarised excitation and fluorescence spectra of the parent hydrocarbon, [5]-helicene (dibenzo[c,g]phenanthrene). The transition energies and dipole and rotational strengths of [5]-helicene have been calculated in the π–SCF approximation, using a general helix model and a model based on X-ray diffraction data for the molecular structure and a constant and a bond-length-dependent π-resonance integral. It is found that the theoretical spectroscopic quantities are not sensitive to the choice of structural model or of a constant or variable β-value, and that their relative values are in satisfactory agreement with experiment. It is concluded that (–)-[5]-helicene has the stereochemical form of a segment of a left-handed helix, and that the (+)-isomer of the derived 9,10-dicarboxylic acid has the enantiomorphic configuration.