Theoretical Analysis of the Intermolecular Interaction Effects on the Excitation Energy of Organic Pigments: Solid State Quinacridone

Abstract

Quinacridones (QAs) are organic hydrogen-bonded pigments, which are yellow in solution and become reddish to violet in solid phase depending on the crystal structure. We have carried out regular and fragment molecular orbital (FMO) based time-dependent density functional theory (TDDFT) calculations of the alpha (I), beta, and gamma crystalline phases of QA to examine the origin of the spectral shift in the solid phase. On the basis of the TDDFT calculations, we have found that the spectral shift from gas to solid phase in QA is dominated by the interplay of the structural deformation, electrostatic potential (crystal field), and intermolecular interactions, and each contribution is of the same order of magnitude. The spectral shift induced by the structural deformation is mainly caused by the stretch of the CO bond. The individual intermolecular interactions contribute to bathochromic and hypsochromic shifts depending on the spatial orientation, and their sums result in the bathochromic shift overall.

Challenges in large scale quantum mechanical calculations

“…For example a new fragmentation scheme for fractioned bonds was developed and applied to the adsorption of toluene and phenol on zeolite; Si nanowires have also been studied using FMO . FMO may also be used for excited calculations, e.g., in combination with TDDFT, which has been tested for solid state quinacridone …”

Fragmentation Methods: A Route to Accurate Calculations on Large Systems

“…Huang et al 567 applied the KEM/MP2/6-31G(d,p) method to investigate the interactions in the crystal of two molecules TDA1 and RangDP52. Fukunaga et al 568 applied the FMO/TDDFT/6-31G(d,p) method to investigate the role of intermolecular interactions upon the excitations energies in three isomers of quinacridone crystals. To facilitate calculations and make them more realistic, an embedding model was used, in which a cluster of quinacridone molecules was immersed in the field of a large number of atomic charges, computed with the BLYP functional and periodic boundary conditions, with the 6-31G(d,p) basis set.…”

Assessing the accuracy of many-body expansions for the computation of solvatochromic shifts

“…Hirata et al 27 computed the vertical excitation energy of formaldehyde in a large water cluster. Recently, Kitaura and coworkers 35,36 have applied their own fragment molecular orbital (FMO) approach to the computation of excitation spectra. The formaldehyde molecule in solution has also been studied under this approach 37 .…”