Second harmonic generation in nonlinear optical crystals formed from propellane-type molecules†
Propellanes form a large family of compounds having a propeller-like shape. Members of this family, which crystallize in the noncentrosymmetric space group, could be interesting for second-order nonlinear optics; however, their properties have not gained much attention yet. Here, we report on 16,20-dinitro-(3,4,8,9)-dibenzo-2,7-dioxa-5,10-diaza[4.4.4]propellane which exhibits a high second-harmonic generation efficiency when excited with nanosecond pulses of λ = 1064 nm infrared light. We performed quantum chemical calculations to determine the origin of the optical nonlinearities in this material at microscopic as well as macroscopic levels using the model of Zyss and Oudar. Although the molecule lacks the typical D-π-A architecture, its crystal phase exhibits a second-order harmonic generation intensity that is almost 40 times larger than that of urea; it can thus be favorably compared with the best NLO organic molecular crystals.