Solvent-Mediated Structural Modulation for Excited-State Relaxation in In-Based Hybrid Halides

Organic-inorganic metal halides (OIMHs) provide a versatile platform for regulating excited-state processes through structural design. Herein, four In-based OIMHs, (C7H12N2)InCl5(H2O)·H2O (1), (C7H10N2)InCl3(C3H7NO) (2) and (C7H10N2)2In2Cl6 (3), and [(C7H10N2)InBr4][(C7H10N2)2InBr2] (4), were synthesized via solvent-controlled crystallization using 2-[(methylamino)methyl]pyridine as the organic component. Changing the crystallization solvent modulates ligand protonation, In-N/O coordination, and In-halide connectivity, giving rise to distinct coordination motifs and intermolecular confinement. Specifically, HCl favors ligand protonation and In-Cl coordination, whereas N,N-dimethylformamide and acetonitrile promote In-ligand coordination. Such solvent-induced structural modulation enables the excited-state relaxation pathways to be tuned without heterometal incorporation. Three chlorides (1-3) exhibit blue prompt emission accompanied by green room-temperature phosphorescence. The bromide (4) displays excitation-independent yellow emission centered at 555 nm under dual excitation channels, together with a second-harmonic generation response. Spectroscopic analyses and theoretical calculations reveal that the emissions are associated with halide-to-organic charge-transfer-related excited states, whose relaxation is governed by local coordination geometry and intermolecular interactions. This work provides an effective solvent-mediated strategy for tuning both prompt and long-lived emissions in OIMHs.