Rigorous Franck–Condon absorption and emission spectra of conjugated oligomers from quantum chemistry

Abstract

A harmonic Condon approach is used to calculate excitation and emission band shapes for the lowest dipole-allowed electronic transitions in conjugated oligomers: polyenes, oligorylenes, and para-phenylenevinylenes. Ground- and excited-state adiabatic energies, equilibrium structures, and vibrational modes are obtained within standard all-valence-electron molecular Hamiltonian incorporating extended configuration interaction. The interstate distortion is cast in normal coordinates and used to calculate transition probabilities from the zero-phonon initial state to the vibrational manifold of the final state. Spectral profiles are obtained as a superposition of Lorentzian line shapes. Theoretical band shapes reproduce prominent features in the absorption and fluorescence spectra of the oligomers in question. The strength of the bond-stretching vibronic progression increases with oligomeric length in polyenes, but decreases in para-phenylenevinylenes. In line with experiment, absorption and emission band shapes of para-phenylenevinylenes are obtained intrinsically nonsymmetric due to stiffening of the accepting vibrational modes in the excited state. The Stokes shifts of the apparent 0-0 features in the latter are reproduced and traced back to relaxations in slow, ring-torsional motions.

Isotopic effect and temperature dependent intramolecular excitation energy transfer in a model donor–acceptor dyad

“…Common to both, however, are contributions from modes around 1600 cm −1 and 1800 cm −1 . These correspond to the C=C bond stretching modes and are consistent with the the vibronic fine-structure peaks observed in most conjugated polymer systems 18,19 . Fig.…”

A joint theoretical and experimental study of phenylene–acetylene molecular wires

“…This can be readily done within the Condon approximation for displaced multidimensional harmonic oscillators [20,33]. The vibrational overlap integrals | 0|ν n | 2 = e −Sn S ν n ν!…”

“…These quantities, in turn, depend on the dimensionless displacements ∆ n of each normal mode with HuangRhys factors, S n = ∆ 2 n /2. The fluorescence band shape as a function of the frequency ω is determined by the imaginary part of the polarizability [20,33] …”

“…Even more accurate TD-DFT approaches are able to tackle complicated electronic features such as exciton binding energy [16,17,18] and double excitations [19]. Furthermore, based on the results of the calculations, absorption an emission spectra can be modeled, for example, for polyenes, oligoarylenes, phenylenevinylenes, and polyfluorenes [10,20,21]. Existing theoretical studies of phenylene-acetylene include TD-DFT investigation of the excited states of the monomer [22,23] and several studies of dendrimer with phenylene-acetylene being the basic unit [24,25].…”

Theoretical predictions of red and near-infrared strongly emitting X-annulated rylenes

“…Theoretically Karabunarliev et al studied the oligorylenes by using different semiempirical and concluded that for quaterrylene, the optically opaque state becomes the lowest excited state adiabatically, not vertically, while for shorter rylenes, the lowest excited states are dipole-allowed both adiabatically and vertically. [28][29][30] Therefore, there certainly occurs a 1Bu/2A g crossover when elongating oligorylenes length, and terrylene and quaterrylene may be both close to the crossover point.…”