Tuning covalent bonding in zinc-based hybrid halides towards tunable room-temperature phosphorescence

Organic-inorganic metal halides with tunable and state room-temperature phosphorescence (RTP) properties in advanced luminescent materials have received broad interest. Herein, 2-(methylamino)pyridine (MAP), 2-[(methylamino)methyl]pyridine (MAMP), and 2-(2-methylaminoethyl)pyridine (MAEP) were designed and hybridized with Zn²⁺ and Cl^-/Br^-, yielding 11 hybrid materials. MAP-based compounds, with a narrow bandgap (3.57 eV), exhibit limited RTP due to inefficient intersystem crossing (ISC) and unstable triplet excitons. In contrast, MAMP (4.49 eV)- and MAEP (4.50 eV)-based compounds achieve enhanced RTP through bandgap alignment with Zn halides, enabling efficient energy transfer, ISC, and triplet exciton stabilization via strong hydrogen bonding and π-conjugation effects. Covalent bonding in MAMP and MAEP compounds provides greater rigidity and exciton stability than hydrogen-bonded systems, resulting in prolonged afterglow durations, while Br-bonding enhances ISC and spin-orbit coupling (SOC), and the weak interactions increase non-radiative decay, further reducing afterglow duration. Density functional theory calculations confirm the enhanced SOC in MAMP and MAEP compounds, further improving RTP efficiency. This work demonstrates the precise control of RTP properties, highlighting the potential in advanced anti-counterfeiting and emerging photonics applications.