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

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.