Emergence of Structural Phosphorescence in Free-Standing, Laterally Organized Polymer Nanofiber Membranes

Abstract

In the past decade, the phosphorescence of metal-free confined polymer structures has generated interest in optoelectronics due to their sustainability, low toxicity, and deployment in sensing applications. Herein, a free-standing array of laterally organized nanofibers was prepared via templated chemical vapor deposition polymerization into a liquid crystalline (LC) phase, and their optical properties were compared to compositionally identical films. The fibers converge into laterally aligned membranes that maintain a high internal order despite the surfaces of the membranes remaining uniform and closed. The membranes consisted of hourglass-shaped nanofibers with features in the micro- and nanometer regime. Free-standing nanofiber membranes differ from polymer films of equivalent chemical composition in several key features: (1) Anisotropic growth of polymer nanofibers with constraint and compliance to an LC template, (2) a high surface-to-volume ratio, and (3) the occurrence of a long-lived emission in the blue region, which persists for multiple seconds after excitation. This study constitutes the first report of long-lived emission from solid-state poly(p-xylylenes) nanofibers. Prospective applications of morphologically controlled polymer arrays with structural luminescence include organic sensors and optoelectronic devices.