Visible-Light-Activated Multi-Color Tunable Time-Dependent Afterglow Triggered by Variable Conjugation Effects via the Transformation of Matrix.

Achieving multi-color tunable time-dependent afterglow color (TDAC) in pure organic materials under visible light excitation remains a significant challenge. Herein, TDAC composites (CDs/U) are prepared with multi-color tunability upon visible-light excitation. Furthermore, the TDAC mechanism is the coexistence of shorter-lived afterglow and longer-lived afterglow. The long- and short-wavelength afterglow in CDs/U originate from highly conjugated nitrogen heterocyclic structures and abundant surface functional states, respectively. More impressively, p-CDs/U systems (p-phenylenediamine (p-PD) as carbon source) exhibit dynamic TDAC behaviors with different decay rates of long-wavelength red afterglow as varying the reaction temperature varies. The experimental results indicate that the transformation of the matrix from biuret to ammelide and then to cyanuric acid (CA) decreases the conjugation degree of p-CDs/U systems owing to the lower pyrrolic N content. This is not conducive to long-wavelength emission, leading to shorter lifetimes in the long-wavelength region. Meanwhile, the theoretical calculation confirms that the matrix is critical for efficient thermally activated delayed fluorescence (TADF). Moreover, the three composites exhibit distinct TDAC behaviors because p-PD and o-PD develop higher conjugation during CDs formation compared to m-PD. Finally, benefiting from the excellent TDAC characteristics of these composites, we have successfully developed multi-mode anti-counterfeiting and multi-dimensional encryption.