Synthesis, spectroscopic studies and quadratic nonlinear optical characterisation of methoxy and aldehyde-substituted calix[4]arene

5,17-Di-tert-butyl-11,23-diformyl-26,28-dimethoxycalix[4]arene-25,27-diol (1) has been synthesised, and then characterised via elemental analysis, X-ray diffraction and MALDI-TOF mass spectrometry analyses, and also FT-IR, Raman, 1H NMR, 13C NMR, UV–Vis spectral techniques. The density-functional theory (DFT) has been utilised to calculate the electric dipole moment (µ), dispersion-free dipole polarisability (α) and second-order hyperpolarisability (β) values for 1. The maximum one-photon absorption, vibrational frequency and NMR chemical shift descriptions of 1 have been also evaluated employing computational chemistry. Both simulated and also measured UV–Vis, vibrational, NMR spectra for title calix[4]arene have been introduced. Additionally, the conclusions of observed and simulated spectra have been evaluated together so as to assert the accordance among them. It has been ascertained that the examined material has reasonably great quadratic hyperpolarisability, indicating quite well second-order optical nonlinearity behaviour. The highest occupied molecular orbitals (HOMOs), the lowest unoccupied molecular orbitals (LUMOs) and HOMO–LUMO energy gaps of title structure have been appreciated from DFT.