Absorption and circular dichroism spectra of dimeric systems. Extended dimer model

Abstract

An extended dimer model is formulated. It differs from the simple dimer model in allowing for mixing of monomer electronic states by intermolecular interaction. The exact and approximate mathematical treatments of the model are discussed in detail. The model is applied to studies of absorption and circular dichroism spectra of dimers. It is shown that the transfer of intensity and rotatory power due to interstate mixing leads to readily observable changes in the vibronic structure of the corresponding spectra. The model is used to reinterpret the observed CD spectra of two different 1,1′-bianthryls.

Analysis of the vibronic fine structure in circularly polarized emission spectra from chiral molecular aggregates

“…Some studies on vibronic effects in CD have appeared, [29][30][31][32] yet no detailed analysis of vibronic effects in CPL has been given. As fluorescence usually occurs from the lowest electronically excited state, CPL spectra are often considerably easier to interpret than CD spectra since they involve only a single electronic transition.…”

Circular Dichroism Study of the Light-Harvesting PCP Complexes Within the Vibronic Multistate Dimer Theory

“…Thus, for a given vibronic transition, the absorption and rotatory ' 621 strength expressions(1) will contain not one [11] but many terms of different electronic origin. For a dimer with achiral monomers we can write [12,13] where the sums run over an arbitrary number of monomer states contributing to interstate couplings. D(i, j, ±) and R(i, j, ±) depend on the symmetry of the monomer electronic states as well as on the geometry of the dimer.…”

“…So, we safely assume that Ψ0 can be adequately represented in the Born-Oppenheimer approximation. It does not apply to the excited states because Ψv ± must account for vibronic coupling [10] as well as the couplings of the excited electronic states introduced by the monomer-monomer interaction operator -Vint [12]. Thus, for a given vibronic transition, the absorption and rotatory ' 621 strength expressions(1) will contain not one [11] but many terms of different electronic origin.…”

“…These integrals can be simply found since the vibrational functions Φ + and Φ",± satisfy the vibronic equation [12] which is readily numerically solvable for given values of the resonance interacting energies (Davydov splittings) Vm and Vn as well as the interstate coupling parameter Vmn [1. 2, 13].…”

“…To this end we use the vibronic dimer theory formulated and applied earlier [8,12]. In particular we wish to show that the principal chiral properties of PCP complexes observed in the range of 15000-25000 cm-1 can be understood when the peridinin dimer acting in PCP as prosthetic group has the geometrical structure as shown in Fig.…”