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

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, (C 12 H 9 N 2 )PbCl 3 , (C 12 H 9 N 2 )SbCl 4 , and (C 12 H 9 N 2 ) 2 InBr 4 ·Br, were synthesized. Initial space group assignments were centrosymmetric for (C 12 H 9 N 2 )PbCl 3 and (C 12 H 9 N 2 )SbCl 4 . However, under 1550 nm laser excitation, (C 12 H 9 N 2 )PbCl 3 and (C 12 H 9 N 2 )SbCl 4 exhibited second harmonic generation intensities ∼1.7 times greater than that of the benchmark KH 2 PO 4 . Structural reevaluation ultimately confirmed non-centrosymmetric P 1 and P 2 1 space groups for (C 12 H 9 N 2 )PbCl 3 and (C 12 H 9 N 2 )SbCl 4 , respectively. Upon excitation at 335 nm and 470 nm, (C 12 H 9 N 2 )PbCl 3 , (C 12 H 9 N 2 )SbCl 4 , and (C 12 H 9 N 2 ) 2 InBr 4 ·Br emit fluorescence at room temperature. (C 12 H 9 N 2 ) 2 InBr 4 ·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.