(187o) Luminescence of Aramid Nanofibers

Aramid nanofibers (ANFs) and their complex networks have been investigated in various fields such as energy devices, sensors, and biomaterials due to their exceptional mechanical strength, thermal and electrical insulation, and sustainability. The combination of these multiple properties originate from the semi-crystalline domains of individual ANFs as well as from the highly interconnected structure of the fiber network. Despite extensive research into the diverse functionalities of ANF networks, their luminescence behavior has yet to be explored.
ANFs are typically regarded as non-luminescence materials due to their intrinsic molecular structure, which features large bandgaps and short pi-conjugation lengths. The planar aromatic rings and amide groups form tightly ordered stacking that leads to highly localized electronic states. Moreover, non-sufficient molecular rigidity in ANFs promote vibrational and rotational molecular behaviors, which cause non-radiative energy transitions and inhibit radiative emission. However, the re-protonation process leads to the formation of aromatic stacks , which increases the pi-conjugation length with electron delocalization. The nanoscale fibers also limit vibrational and rotational motions of the molecules, making radiative energy transitions more efficient.
We demonstrates the emergence and spectral properties of bright emerald luminescence from ANF networks and single fibers. This luminescence is strongly influenced by the polarity and protic nature of the solvent used in the re-protonation process. This study lays the groundwork for understanding the luminescence behavior of ANFs. Based on these insights, future research may explore blending ANFs with other materials to further investigate the relationship between structural organization and luminescence properties. Additionally, controlled structural modifications could enable the tuning of luminescence color. Such advancements will contribute significantly to the development of next-generation optoelectronic devices, including high-strength and flexible luminescent wearable sensors.