Ab Initio Studies of Aromatic Excimers Using Multiconfiguration Quasi-Degenerate Perturbation Theory

Abstract

The aromatic excimers of benzene, naphthalene, anthracene, pyrene, and perylene are systematically investigated using the multiconfiguration quasi-degenerate perturbation theory (MCQDPT) method, which is one of high-level ab initio quantum chemical methods. The reference configuration space for MCQDPT is carefully designed for an appropriate description of the target electronic state with a tractable computational cost. The dimers with eclipsed parallel arrangement are investigated. The basis set dependence of the selected spectroscopic parameters is examined for the benzene and naphthalene dimers, and that of the excimer binding energy is found to be significant. In contrast, the equilibrium intermolecular distance and excimer fluorescence energy are less sensitive to the size of the basis sets used, and they agree with the corresponding experimental values, even with a nonextensive basis set size. The calculated spectroscopic parameters for anthracene, pyrene, and perylene dimers are also in good agreement with the experimental results. The electronic properties of the excimers are discussed in relation to those of the corresponding monomers. The wave functions of the excimers are analyzed in detail to clarify the origin of the attractive nature between the two monomers.

Excited State Relaxation of Neutral and Basic 8-Oxoguanine

“…XMCQDPT has been used previously to yield energies that are in excellent agreement with experiment for small biological systems. [21][22][23] The active spaces in the XMCQDPT calculations are the same as those used in our MRCI calculations.…”

Spectroscopic Properties of Naphthalene on the Surface of Ice Grains Revisited: A Combined Experimental–Computational Approach

“…69 A smaller value of 0.300 nm was found with CC2 69 and the multi-configurational quasi-degenerate perturbation theory methods. 70 All values fall into the experimentally observed range of 0.300-0.360 nm. 55 .…”

A Theoretical Study of the Formation of Benzene Excimer: Effects of Geometry Relaxation and Spin-state Dependence

“…Previous results state that this is due to the strong molecular orbital interactions; as molecules come closer, molecular orbital interactions becomes stronger such that HOMO is destabilized while LUMO is stabilized, leading to significantly reduced HOMO-LUMO gap and hence reduced transition energy. 25,26 It is also found to be intriguing that molecules interact even stronger in S 1 state than T 1 state in this configuration. This might be ascribed, in part, to the fact that the localized nature of triplet wavefunction 36,37 weakens to some extent the electronic coupling between two localized triplet states, i.e., state for the dimer with one molecule in T 1 state and the other in the ground state and vice versa.…”

“…4,5,15 In this regard, intermolecular interactions in the excited states attract attention increasingly. 2,3,8,10,[16][17][18][19][20][21][22][23][24][25][26] As for recent theoretical studies of intermolecular interactions in the excited states, various acene molecules including benzene were employed. 9,18,[20][21][22][24][25][26][27] Most of those studies, however, rely on the frozen molecular structures derived from the ground-state calculations and thus the geometric relaxation effects have been neglected.…”