Exceptionally high NLO response and deep ultraviolet transparency of superalkali doped macrocyclic oligofuran rings

Abstract

Cyclic oligofurans containing five and six furan rings (5CF & 6CF) doped with superalkalis are presented here as a new type of NLO material. The OLi₃@nCF, ONa₃@nCF and OK₃@nCF (n = 5 & 6) complexes are optimized at the M05-2X/6-31+G(d,p) level of theory. In these complexes, the superalkalis maintain their identity, and interact through the cavity of the cyclic oligofurans (nCF). Nonlinear optical properties are obtained through first hyperpolarizability (β_o) of the complexes. The NLO response is rationalized on the basis of dipole moment (μ_o), energies of crucial excitation states (E_ex) and vertical ionization energies (VIE). The highest hyperpolarizabilities (β_o = 5 × 10⁷ a.u. and β_vec = 3 × 10⁷ a.u.) are observed for OK₃@nCF complexes along with the lowest E_H–L, prominent NBO charge transfer, the highest dipole moment, and pronounced polarizability. The remarkable NLO response is attributed to the generation of excess electrons by superalkali doping. UV-Vis spectra are calculated to realize the transparency of these complexes in the UV-Vis region. The results suggest that higher NLO response is obtained when superalkalis are doped in higher oligofurans.