Cyano-Based Materials with Giant Optical Anisotropy and Second Harmonic-Generation Effect

It is a huge challenge to achieve giant optical anisotropy (e.g., birefringence) over a wide region from infrared (IR) to ultraviolet (UV) spectroscopy. This is mainly due to the lack of ideal optical motifs, which should have giant structural anisotropy with a wide transparent range. Especially in the field of nonlinear optical (NLO) materials, polar motifs with giant optical anisotropy are extremely scarce, but they are favorable to exhibit strong second harmonic generation (SHG) effect and phase-matching capacity. On the basis of analysis of microstructure and macro optical property, in this study, we focus on one-dimensional chained cyano (CN) motif and surprisingly find that it can exhibit sufficiently large optical anisotropy and SHG effect from IR to UV regions. Therefore, it is reasonable to believe that the CN motif can be considered as a novel NLO material gene, which was totally ignored in the previous studies. Interestingly, the CN-gene can be integrated into various coordination structures, such as metal cyanides, cyanogen halides, and cyanogen chalcogenides, to promote these materials to exhibit tunable NLO capabilities from IR to UV and deep-UV regions. Remarkably, the chained acentric CNI structure, which has already been obtained in the experiment, can achieve the IR and UV frequency conversion with a sufficiently large SHG effect (similar to 17 pm/V) and a giant optical birefringence (similar to 0.7 at 1064 nm). Therefore, the cyano-based compounds proposed in this article can not only enrich the structural chemistry of NLO materials, but also potentially advance the development of optical material genome project.