Tuning of nonlinear optic response properties for ruthenium alkynyl complexes via computational-guided structural tailoring

Abstract

Hartree Fock (HF) and density functional theory (DFT) methods based on a 3-21G set level were used to computationally assess the nonlinear optic (NLO) response of six ruthenium (Ru) arylalkynyl complexes. The low basis set of 3-21G was proved to provide adequate results with difference of only about 3% between calculation and experimental data. Substitution of Ru-phenyl with six simplified models of Ru-H and Ru-methyl complexes revealed that DFT-based calculations were more accurate than HF in estimating the NLO response. The calculated bond lengths and angles of Ru-methyl were in good agreement with Ru-phenyl. Given that the calculated C≡C stretching vibration and UV-vis maximum absorption for Ru-methyl was comparable to Ru-phenyl, with values corresponding to 2154.56 cm-1 and 460.93 nm, respectively. It was evident that Ru-H, Ru-methyl and Ru-phenyl complexes undergo intraligands π-π* and Laporte forbidden metal d-d transition. Henceforth, it is affirmed that calculations using simplified Ru-H complexes were as much as reliable as the full structure of Ru to assess the NLO response. Assessment of electron inductive effect on Ru-carbonyl (Ru-Co), Ru-cyclopentadienyl (Ru-Cp) and Ru- bipyridine (Ru-bpy) complexes revealed two absorption maxima that appeared in regions 320−375 nm and 382−460 nm, which represent an intraligand π-π* orbital and Laporte forbidden d-d-transition, respectively. Migration of electrons from Ru center to the bipyridine ligand suggests a greater electron acceptor effect than Ru center to the arylalkynyl group. However, Ru conjugated to an electron withdrawing group i.e. carbonyl tend to render lower NLO response while elevating HOMO - LUMO energy gap and Ru to Cα bond lengths.