A computational expression for the Faraday A term of magnetic circular dichroism (MCD) is derived within coupled cluster response theory and alternative computational expressions for the B term are discussed. Moreover, an approach to compute the (temperature-independent) MCD ellipticity in the context of coupled cluster damped response is presented, and its equivalence with the stick-spectrum approach in the limit of infinite lifetimes is demonstrated. The damped response approach has advantages for molecular systems or spectral ranges with a high density of states. Illustrative results are reported at the coupled cluster singles and doubles level and compared to time-dependent density functional theory results.
Raman
and Raman optical activity (ROA), IR, and vibrational circular
dichroism (VCD) spectra of (
R
)- and (
S
)-pantolactone have been recorded in three solvents. ROA has been
employed on water and DMSO solutions, VCD on DMSO and CCl
4
solutions. In the last solvent, monomer–dimer equilibrium
is present. Due to the low conformational flexibility of the isolated
molecule and to the possibility of aggregation, this compound has
been used here to test different protocols for computation of the
spectroscopic responses taking into account solvent effects. Molecular
dynamics (MD) simulations have been carried out together with statistical
clustering methods based on collective variables to extract the structures
needed to calculate the spectra. Quantum mechanical DFT calculations
based on PCM are compared with approaches based on different representations
of the solvent shell (MM or QM level). Appropriate treatment of the
solvent permits obtaining of good band-shapes, with the added advantage
that the MD analysis allows one to take into account flexibility of
dimeric structures justifying the broadness of observed bands and
the absence of intense VCD couplets in the carbonyl and OH stretching
regions.
The magnetic circular dichroism (MCD) spectra of metal complexes of tetrakis(thiadiazole)porphyrazines ([TTDPzM] with M = 2HI, ZnII, MgII(H2O), and CdII) have been recorded in dimethyl formamide solution. Together with the UV–Vis spectra, the MCD spectra provide useful information about the structure and electronic properties of the complexes. The experimental UV–Vis and MCD spectra compare pretty well with DFT calculations of two sorts, based either on the sum‐over‐states (SOS) approach or on the complex polarization propagator approach. They further corroborate the findings and interpretation of MCD spectra of porphyrazines based on the model of Michl for peripheral molecular orbitals. Magnetic circularly polarized luminescence (MCPL) spectra, quite uncommon in the literature, have been recorded for [TTDPzM] (M = 2HI, ZnII, MgII(H2O)).
With the aim of finding and characterizing new simple organic molecules (SOM) generating circularly polarized luminescence (CPL), we test here nine [2]paracyclo[2](5,8)‐quinoliphane derivatives, whose circular dichroism (CD) spectra were previously measured at short wavelengths in a study encompassing also OR and VCD (CD in the IR). Completion of the CD spectra is carried out with attention paid to weaker and longer wavelength features. The observed signs of the CPL spectra are compared to the signs of the CD band at the longest wavelength and are found coincident except in two cases. The magnitudes of dissymmetry ratios g in luminescence are of the order 10−3, like the corresponding |g| values for the absorption case. TD‐DFT calculations for the two simplest cases provide details on the molecular orbitals involved in the transitions responsible for the observed signals of these molecules. The calculations allow us to provide also a first explanation of the two observed behaviors of the |glum|/|gabs| ratios.
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