Quantum mechanics

Valence (chemistry)

Engineering

Chemical physics

Photochemistry

Materials science

Density functional theory

Crystal structure

Thermal expansion

Chemical engineering

Quenching (fluorescence)

Thermodynamics

Bipyridine

Physics

Organic chemistry

Thermal

Luminescence

Fluorescence

Computational chemistry

Negative thermal expansion

Crystallography

Chemistry

Optoelectronics

Journal of the American Chemical Society

Overcoming thermal quenching is an essential issue in the practical application of luminescent materials. Herein, we found that negative thermal expansion (NTE) can achieve the thermal enhancement of luminescence in molecular materials based on three metal-organic frameworks CuX-bpy (X = Cl, Br, I; bpy = 4,4'-bipyridine). All complexes exhibit NTE on the c-axis, and the strongest NTE leads to a contraction of the Cu...Cu distance in CuCl-bpy, which further intensifies the luminescence emission. This phenomenon indicates the existence of thermally enhanced charge transfer. Moreover, the origin of the distinction in charge transfer attributed to the different valence states of the copper is investigated through the combined studies of X-ray photoelectron spectroscopy, X-ray absorption near-edge structure, and density functional theory calculations. This research provides a new approach to modulating the luminescence thermal enhancement by NTE.

Thermal Enhancement of Luminescence for Negative Thermal Expansion in Molecular Materials