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

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─(CH2)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.