Conferring High Luminescence and Photophysical Stability on a Eu ³⁺ Tetrakis(β-Diketonate) with the Bis(triphenylphosphine)iminium Cation

Lanthanide complexes of sufficient luminescence and stability are highly desirable for a wide variety of fields. We successfully synthesized a tetrakis(β-diketonate) complex, <b>PPN[Eu(TTA)</b>_<b>4</b><b>]</b> (TTA: thenoyltrifluoroacetone, PPN: bis(triphenylphosphine)iminium). The as-synthesized complex exhibits superior luminescence properties compared with its sodium analog (Na[Eu(TTA)₄]) with a higher PLQY (77.4% vs 21.6%) and an extended fluorescence lifetime (0.61 ms vs 0.22 ms) as well as the enhanced stability including a higher thermal decomposition onset (280 °C) and markedly greater photostability (>95% intensity retained after 120 h sunlight). The enhanced photoluminescence is attributed to the PPN⁺, which reinforces molecular rigidity to suppress nonradiative decay and optimizes Eu³⁺ coordination microenvironment to promote ligand-to-metal energy transfer. When applied to latent fingerprint (LFP) visualization, <b>PPN[Eu(TTA)</b>_<b>4</b><b>]</b> emits high<b>-</b>contrast red luminescence under 365 nm ultraviolet (UV) excitation, enabling clear resolution of all three levels of fingerprint features (ridge patterns, detail points, and sweat pores) on diverse substrates (porous, nonporous, and semiporous). Preliminary studies further demonstrate that <b>PPN[Eu(TTA)</b>_<b>4</b><b>]</b> possesses efficient X-ray radioluminescence, suggesting potential cross-application in hidden fingerprint detection. This work clarifies the critical role of PPN⁺ in regulating Eu³⁺ complex performance and provides a novel strategy for developing high-performance luminescent materials for forensic science and optical engineering.