In addition to π – conjugated groups, non – π – conjugated groups, such as PO4, SO4, are also extremely important systems to explore new deep ultraviolet (DUV) nonlinear optical (NLO) crystals. However, most of the reported NLO phosphates and sulfates either display weak second-harmonic generation (SHG) responses (< 2 × KH2PO4 (KDP)) or little birefringence, in spite of their short cut-off UV edges.
It is a great challenge to design and synthesize non-π-conjugated DUV NLO crystals with desired SHG coefficients (> 2 × KDP) and moderate birefringence.
In a study published in Angew. Chem. Int. Ed., the research group led by Prof. YE Ning from Fujian Institute of Research on the Structure of Matter (FJIRSM) of the Chinese Academy of Sciences reported a new polar non-π-conjugated group, viz. (NH2SO3)–, as a DUV NLO-active functional unit based on the first-principles studies.
The calculation results revealed that the (NH2SO3)– group is superior to (SO4)2- group due to its obvious polarizability anisotropy, large hyperpolarizability (approximately 1.92 times larger than that of (SO4)2- group) and wider HOMO-LUMO gap of 8.17 eV (corresponding to the absorption edge of 152 nm).
In order to verify the calculation results, the researchers combined alkaline-earth metals with (NH2SO3)– group to synthesize two DUV transparent NLO sulfamates, M(NH2SO3)2 (M = Sr, Ba).
Optical properties measurements showed that M(NH2SO3)2 (M = Sr, Ba) have outstanding linear optical and NLO properties including strong SHG responses (1.2 and 2.7 ×KDP), short UV cut-off edge (< 190 nm) and moderate birefringence (firstname.lastname@example.org nm for Sr(NH2SO3)2).
Besides, the researchers successfully grew the large size single crystals of M(NH2SO3)2 (M = Sr, Ba) by constant temperature solution evaporation method, which indicated that they have great application values.
This study has provided not only two promising DUV transparent NLO crystals, but also an innovative non-π-conjugated unit for developing more DUV transparent NLO materials.
Reference: Dr. Min Luo, Dr. Chensheng Lin, Donghong Lin, Prof. Ning Ye, “Rational Design of the Metal‐Free KBe2BO3F2⋅(KBBF) Family Member C(NH2)3SO3F with Ultraviolet Optical Nonlinearity”, Angew. Chem. Int. Ed. 2020, 59, 15978. https://onlinelibrary.wiley.com/doi/abs/10.1002/anie.202006671
Provided by Chinese Academy of Sciences