Nanostructural Engineering of Glassy Oligoporphyrin Arrays for Near-Infrared-II Luminescence via Supramolecular Polymerization

Solid-state near-infrared (NIR) luminescence beyond 1000 nm (NIR-II) was achieved through the supramolecular polymerization of glassy oligoporphyrin arrays ( 1 – 4 ) in spin-coated films. Supramolecular polymerization proceeded during solvent evaporation from toluene, resulting in the NIR-II-luminescent nanostructure. The thermodynamics of supramolecular polymers was characterized in detail in solutions by a judicious choice of a solvent system comprising toluene and cyclohexane to modulate the solvation energy. The molecular arrangements in spin-coated films were elucidated by atomic force microscopic and synchrotron grazing-incidence wide-angle X-ray diffraction experiments. Collectively, the experimental observations revealed the formation of multiple cofacial π-stacking interactions with the interdigitation of bulky alkyl side chains. Beyond the static nanostructural features, the significant Stokes shifts observed in the NIR luminescence of 1 – 4 underscore a strong coupling between exciton dynamics and excited-state structural relaxation within the glassy supramolecular porphyrin polymers, ultimately leading to solid-state NIR-II photoluminescence.