(SO3CF3)−: A Non-π-Conjugated Motif for Nonlinear Optical Crystals Transparent into the Deep-Ultraviolet Region

The search for new ultraviolet (UV) or deep-UV nonlinear optical (NLO) crystals would greatly prompt the development of laser science and technology. As the NLO performance of these crystals is mainly determined by the anionic groups, herein the (SO 3 CF 3 ) − group is highlighted as a promising non-π-conjugated NLO-active motif with excellent deep-ultraviolet (DUV) transmission and good NLO properties. First-principles studies reveal that this group possesses the largest HUMO-LOMO gap among the (SO 4 ) 2− -based units, as well as a relatively large NLO response. The further experiments demonstrate that the CsSO 3 CF 3 compound containing the (SO 3 CF 3 ) − motif exhibits th UV cutoff edge below 200 nm and an NLO effect ≈0.8× KH 2 PO 4 , confirming the potentials of this new motif for UV and DUV NLO applications.