Theoretical Study Of Substituent Effects On Electride Characteristics And The Nonlinear Optical Properties

The rapid development of nonlinear optics?NLO?materials in both theoretical research and experimentation has played an important role in promoting the progress of nonlinear optics.It has become an essential component in the fields of optics and electricity.Because of the superior properties of organic nonlinear optical materials,they can exhibit large nonlinear optical responses.In the past two decades,there has been an increasing interest in searching for new organic nonlinear materials,in particular the second-order nonlinear optical?NLO?materials with potential applications in ultrafast modulators and switches,laser frequency conversion devices,surface and interface characterization tools,and biological and chemical sensors.Electrides,a novel kind of ionic compound in which electrons serve as anions,have been proposed as potential second-order nonlinear optical?NLO?material.Among so many molecular electrides that are designed theoretically,Li@calix[4]pyrrole as a representative of molecular electrides is widely reported and investigated.Therefore,the substituent effects on the electride characteristics and the NLO behaviour of molecular electrides were studied theoretically based on the electrides in this paper.The results show that electron-donating and electron-withdrawing groups can effectively increase and decrease the first hyperpolarizability??₀?,respectively,without affecting the electride characteristics?electron population?.More interestingly,lithiation in which four H atoms bonded to N atoms are substituted by four Li atoms within the core structure of Li@calix[4]pyrrole remarkably improves the electride characteristics,with a large electron population of 0.74 e?1.02 e?at the NNA?ELF?basins by the topological analysis of atoms in molecules?AIM?and the electron localization function?ELF?,making this structure perhaps the first formal molecular electride with almost one electron isolated from the rest of the molecules.Furthermore,a relationship between the electride characteristics and the NLO properties is found:the more delocalization the excess electron of the electride experiences,the larger the?₀ value is.The present investigation may provide useful information for exploring high-performance second-order nonlinear optical materials based on organic electrides.