Easily Accessible and Up‐Scalable Aliphatic Bis‐Formamides with Afterglow Luminescence: Photoluminescence Properties and Applications

ABSTRACT Materials based on water‐processable, non‐conjugated organic molecules featuring afterglow luminescence are promising due to their sustainable character and their straightforward upscale. Yet, they remain barely applied in advanced optoelectronics, such as solid‐state lighting and anti‐counterfeiting, because of a lack of mechanistic studies. Herein, we describe a class of terminal bis‐formamide compounds, H(O═)CNH─(CH 2 ) n– HNC(═O)H, that feature a long afterglow with an average excited‐state lifetime (<τ>) close to the second. As an interesting archetype, N,N'‐(hexane‐1,6‐diyl) bis‐formamide ( n = 6, BFAC6 ) exhibits a <τ> of 0.40 s associated with a photoluminescence quantum yield of 13% in both crystalline solid state and polyvinyl alcohol films ( BFAC6@PVA ). Thorough investigations such as temperature‐dependent x‐ray analyses, time‐resolved electronic spectroscopy, and electrochemical impedance spectroscopy suggest that the unusual long‐lived emission could be attributed to rigid packing ruled by H‐bonding, resulting in an emitting excited state attributed to— at least— a H‐trapped emissive state. Moreover, the so‐called clustering‐triggered emission, or clusteroluminescence, is also to be considered here. As a proof of concept, these materials were used for decoration, anti‐counterfeiting, and color down‐conversion for white hybrid light‐emitting diodes, featuring promising performances in terms of device stability, as well as recovery of the initial emission features upon heating–cooling processes.