Complexes of SO3 with Pyridine and Bipyridine: Quantum‐Mechanical Methods for Interactions and Spectroscopy

Abstract

AbstractGround‐ and excited‐state properties of complexes of SO3 with pyridine and bipyridine are studied with quantum‐mechanical approaches, an important endeavor as SO3 complexation is useful for mitigating its environmental impact and for designing photochromic polymers. Guided design of these polymers will benefit from detailed understanding of the performance of quantum‐mechanical methods to be used for such tasks. Therefore, here we study performance of density functional theory (DFT) and time‐dependent DFT (TD‐DFT) for predicting binding energies, relative energies and excitation spectra of pyridine‐SO3 and bipyridine‐SO3 complexes, in the gas phase and solution. Ground‐state properties are compared against DLPNO‐CCSD(T), DLPNO‐CCSD(T)‐F12 and CCSD(T)‐F12 calculations. Excited state properties are compared to second‐order Algebraic Diagrammatic Construction, ADC(2), and experimental data. For ground state properties, dispersion corrections make a massive improvement to computational data, with the revPBE‐D4 functional specifically recommended for its accuracy, ~1.5 kcal/mol error in the gas phase and ~2.8 kcal/mol in ethanol. For excited‐state properties, many density functionals perform quite well for predicting excitation energies, with most of them being range‐separated hybrids or double‐hybrids with spin‐scaled correlation. However, oscillator strengths from these functionals massively differ from ADC(2), with oscillator strengths from lower‐rung functionals like PBE, M06‐L and BP86 closer to ADC(2).