Outstanding NLO response of K3O@thia[n]circulenes; a DFT and molecular dynamics perspective

Abstract

The nonlinear optical (NLO) response of superalkali (K3O) doped thia[7&8]circulenes (1–18) is analyzed through density functional theory (DFT) calculations. The high interaction energies illustrate thermodynamic feasibility of these complexes. Natural bond orbital (NBO) charge analysis confirmed that electronic charge is transferred from K3O toward thia[7&8]circulenes. Additionally, the lowest unoccupied molecular orbital (LUMO)—the highest occupied molecular orbital (HOMO) energy gaps are reduced up to 0.81 eV after doping. Polarizability (α o) and the first hyperpolarizability (β o) values are used to estimate NLO response of doped circulenes. The highest α o and β o obtained for K3O doped thia[7&8]circulene (9) are 7297 au and 3.03 × 108 au, respectively. Two level model illustrates that the excited dipole moment as decisive factor for enhancement of NLO response. The electronic excitation is confirmed from ultraviolet-visible (UV–vis) spectroscopic analysis where all doped circulenes showed bathochromic shift. Ab initio molecular dynamics depicts strong interaction and high thermal stability of K3O doped thia[7]circulene 9. Thus, K3O doping on thia[n]circulenes (n = 7&8) remarkably enhanced the NLO response which assures the use of respective complexes in designing of building blocks for future optics.