Advancing nonlinear optics: discovery and characterization of new non-centrosymmetric phenazine-based halides

Abstract

Organic–inorganic metal halides (OIMHs) have drawn considerable attention due to their remarkable optoelectronic properties and substantial promise for nonlinear optical applications. In this research, phenazine has been selected as the organic cation because of its π-conjugated feature. Three compounds, (C₁₂H₉N₂)PbCl₃, (C₁₂H₉N₂)SbCl₄, and (C₁₂H₉N₂)₂InBr₄·Br, were synthesized. Initial space group assignments were centrosymmetric for (C₁₂H₉N₂)PbCl₃ and (C₁₂H₉N₂)SbCl₄. However, under 1550 nm laser excitation, (C₁₂H₉N₂)PbCl₃ and (C₁₂H₉N₂)SbCl₄ exhibited second harmonic generation intensities ∼1.7 times greater than that of the benchmark KH₂PO₄. Structural reevaluation ultimately confirmed non-centrosymmetric P1 and P2₁ space groups for (C₁₂H₉N₂)PbCl₃ and (C₁₂H₉N₂)SbCl₄, respectively. Upon excitation at 335 nm and 470 nm, (C₁₂H₉N₂)PbCl₃, (C₁₂H₉N₂)SbCl₄, and (C₁₂H₉N₂)₂InBr₄·Br emit fluorescence at room temperature. (C₁₂H₉N₂)₂InBr₄·Br exhibits reversible phase transitions, showing potential for phase change energy storage. Our research underscores the critical role of comprehensive experimental validation in determining the precise crystallographic space groups and reveals the extensive potential of OIMHs as versatile candidates for advanced optoelectronic applications.