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.

Optical Properties of Electrospun Nanofiber Mats

“…Phosphorescence, on the other hand, was suggested as an alternative to electrical light in medical endoscopes [133] or for anti-counterfeiting applications [134], but in most cases it is used as an oxygen sensor [135][136][137][138][139]. Furthermore, other phosphorescent sensors were suggested, such as Zn 2+ phosphorescent sensors [140,141], phosphorescent sensors for humidity [142], or several other physical and chemical stimuli, such as pressure, heat, pH value, explosives, or heavy metal ions [143].…”