Grafting of derivatives of naphthalic anhydride onto amine-modified surfaces of dense nanosilica and their fractal features for luminescent performance

The surfaces of density nano-silica spheres (DNSS) was modified using amine groups, and then novel luminescent DNSS-based materials were successfully synthesized via post-grafting various capacities of perylene-3.4.9.10-tetracarboxylic-dianhydride (PTD) and 4-amino-1,8-naphthalic anhydride (ANA). Meanwhile, their structures and properties were characterized by XRD, SAXS, TEM, N₂ sorption, FT-IR, TG-DTG, Photoluminescence and elemental analysis, as well as time-resolved decays. The results demonstrate that the ANA or PTD is uniformly distributed in the presence of outer surface of amine-modified DNSS. Two characteristic peaks centered at 525 nm and 560 nm with various amounts of surface-grafted PTD belong to aggregate states, comparably, the emission peak for ANA-DNSS samples presents the blue-shift from 520 nm to 504 nm with increasing amount of surface-grafted ANA, indicating the dispersion behaviors of ANA from aggregating to monolayer state. Meanwhile, the fluorescence decay lifetime is around 4.49ns for ANA-DNSS-10, 9.85ns for PTD-DNSS-10, longer than 3.99ns for NA-DNSS-10 in our previous report. Specially, the SAXS patterns show the increase tendencies for surface fractal value with increasing amount PTD or ANA, suggesting the structural irregularities of obtained hybrid materials for before and after surface grafting. These observations demonstrate that the surface effect in the APTES-DNSS matrix play an important role on the fluorescent behaviors.