The effect of Duschinsky rotation on charge transport properties of molecular junctions in the sequential tunneling regime

First-principles study on vibrationally resolved fluorescence of fused 5,15-(diphenyl)-10,20-(dibromo)porphyrin molecule

The vibrationally resolved fluorescence spectrum of a narrow-line single-molecule transducer, fused 5,15-(diphenyl)-10,20-(dibromo)porphyrin (fused-H2P) molecule, has been calculated by time-dependent density functional theory with the inclusion of both Franck-Condon and Herzberg-Teller contributions. Analytical transition dipole derivatives are used for the calculations of Herzberg-Teller terms to eliminate the possible errors caused by numerical differentials. The performance of different exchange-correlation functionals including B3LYP, ωB97X-D, and M06-2X has been examined. The comparison with the high-resolution experimental emission spectrum indicates that all three functionals can satisfactorily describe the fluorescence spectral profile, while ωB97X-D and M06-2X give slightly better excitation energy than B3LYP. Detailed analysis shows that the fluorescence spectrum is dominated by the Franck-Condon contribution, while the Herzberg-Teller term contributes mostly to its low energy tail. It is found that the size of the basis set has limited influence on the fluorescence spectrum, and a standard 6-31G(d, p) basis set is adequate for the purpose. The substitution of terthiophene side chains is found to have minor effects on the fluorescence spectrum. Our study provides unambitious assignments for all the vibronic structures in the experimental spectrum.

Gauge invariant theory for super high resolution Raman images

The use of a highly localized plasmonic field has enabled us to achieve sub-nanometer resolution of Raman images for single molecules. The inhomogeneous spatial distribution of plasmonic field has become an important factor that controls the interaction between the light and the molecule. We present here a gauge invariant interaction Hamiltonian (GIIH) to take into account the non-uniformity of the electromagnetic field distribution in the non-relativistic regime. The theory has been implemented for both resonant and nonresonant Raman processes within the sum-over-state framework. It removes the gauge origin dependence in the phenomenologically modified interaction Hamiltonian (PMIH) employed in previous studies. Our calculations show that, in most resonant cases, the Raman images from GIIH are similar to those from PMIH when the origin is set to the nuclear charge center of the molecule. In the case of nonresonant Raman images, distinct differences can be found from two different approaches, while GIIH calculations provide more details and phase information of the images. Furthermore, the results from GIIH calculations are more stable with respect to the computational parameters. Our results not only help to correctly simulate the resonant and nonresonant Raman images of single molecules but also lay the foundation for developing gauge invariant theory for other linear and nonlinear optical processes under the excitation of non-uniform electromagnetic field.