Fine-Tuning Aromatic Stacking and Single-Crystal Photoluminescence Through Coordination Chemistry

Organic aromatics usually show a decrease in fluorescence efficiency in the solid state on account of well-known aggregation induced quenching. We have found that single crystals of coordination polymers consisting of γ-aminobutyric acid functionalized naphthalenediimide ligand (H ₂ GABA-NDI) can give rise to highly emissive, broad, and red-shifted photoluminescence (PL) in the solid state. To better understand the origin of the bandwidth broadening with the π–π stacking distances, we performed time-resolved PL studies in a series of polymers with a variety of metal centers. We conclude that the broad steady-state PL signals is originated from a superposition of two emissive states with differing energy and lifetimes, with the lower energy one produced by the interchromophoric interactions mediated by π–π stacking of neighboring NDI units. Our work demonstrates that coordination chemistry is an effective tool to modulate interchromophoric couplings and that simple PL analysis can be used as a measure of the degree of π-stacking.