Fluorescent Nanographene-Polystyrene Microlabels for Photonic Applications

Nanographenes (NG) can be described as graphene fragments displaying strong optical transitions in the visible or near-infrared range due to bandgap opening through quantum confinement on lateral sizes of a few nanometers. NGs can be considered as ideal benchmarks to study the optical response of zero-dimensional nanocarbons, sometimes showing non-trivial photophysics [1,2]. From a functional point of view, NGs often display a very bright fluorescence, and their optical properties can be precisely tailored through precise structural engineering with atomic precision. On these grounds, NGs are ideal building blocks of more complex nanocomposites where they can play the role of efficient light harvesters or light emitters. Here we present the result of our recent study [3] focusing on a nanoribbon-shaped NG displaying visible fluorescence with very high quantum efficiency (QY=65%) [1]. We first carried out a thorough characterization of its photocycle by a combination of steady-state, nanosecond and femtosecond time-resolved optical methods. Then, we coupled these NGs with micrometer-sized polysterene spheres (NG@PS), through a simple self-assembly strategy in solution phase. The resulting NG@PS composites show unique fluorescent properties that are very different from those of the starting NGs and pave the way to new applications of nanographenes. [3] In fact, NG@PS fluorescence displays an entirely new set of narrow resonances due to the coupling of NG optical transitions to the whispering gallery modes of the polystyrene microsphere, acting as an optical microresonator. We argue that these NG@PS are a family of functional nanocomposites which would be potentially suitable for several applications, such as micro-sensing or micro-lasers. More specifically, we show that the finely-structured spectral fingerprints displayed by NG@PS are unique for each individual microparticle, such that NG@PS can be used as luminescent unclonable labels for anticounterfeiting applications.<br/><br/>REFERENCES<br/>1. S. Castro-Fernandez et al. Angewandte Chemie 59, 7179, 2020<br/>2. M. Reale et al. Carbon 206, 45, 2023<br/>3. M. Reale et al. Adv Func Mater, 2024, 2402079