From C4H7N2Ge0.4Sn0.6Br3 to C6H11N2Ge0.4Sn0.6Br3: Effective Modulation of the Second Harmonic Generation Effect and Optical Band Gap by Planar π-Conjugated Organic Cation Size

In the search for nonlinear optical (NLO) materials with excellent overall performance, we have devoted ourselves to organic–inorganic hybrids consisting of anionic groups containing stereochemically active lone-pair (SCALP) electron cations and organic planar π-conjugated group cations. Accordingly, in this paper, two novel organic–inorganic hybrid metal halides, C 4 H 7 N 2 Ge 0.4 Sn 0.6 Br 3 (I) and C 6 H 11 N 2 Ge 0.4 Sn 0.6 Br 3 (II), have been synthesized. The powder second-harmonic technique shows that both C 4 H 7 N 2 Ge 0.4 Sn 0.6 Br 3 and C 6 H 11 N 2 Ge 0.4 Sn 0.6 Br 3 have moderately strong second-order nonlinear optical effects, which are about 2.03 (I) and 1.16 (II) times that of KH 2 PO 4 (KDP), respectively. They also have different optical band gaps of 2.75 (I) and 2.88 eV (II) due to the different sizes of the organic cations, and their photoluminescent and thermal properties were also investigated. This work provides new structural insights for the design and modulation of organic–inorganic hybrid halide materials with multiple excellent optical properties.