The geometries and second-order nonlinear optical properties of the four conformers of donor-acceptor-substituted calix[4]arene molecules are investigated by means of semiempirical quantum-chemical techniques. The evolution of the second-order polarizability beta is analyzed with respect to changes in conformation and the theoretical results are compared with electric-field-induced second-harmonic generation and hyper-Rayleigh scattering experimental data. We point out the presence of strong pi-pi cofacial interactions that shift the charge-transfer bands to shorter wavelengths; we rationalize the origin of the blue shift by studying the characteristics of a dimer.