Broad-band emissive phenanthroimidazole-based donor–acceptor luminogens for hybrid white light emitting diodes and sensors for picric acid detection

Abstract

In this study, a series of phenanthroimidazole-based donor–acceptor luminogens were designed and synthesized. Furthermore, their design rationale, molecular structure, and spectroscopic characterization are discussed in detail herein to provide a comprehensive understanding of their various applications, integrating hybrid white LED fabrication and sensing properties (temperature sensing and picric acid detection). We validated our findings through electrochemical analysis, supported by DFT calculations, including the determination of the HOMO–LUMO gap via cyclic voltammetry, and all the synthesized fluorophores were characterized via single-crystal XRD. Among the fluorophores designed and synthesized in this work, PhAn showed superior properties for application in white LED technology. This fluorophore was fabricated on a near-UV LED chip with a precise PMMA : organic fluorophore and Eu complex mass ratio, and the resulting hybrid white LED exhibited an impressive CRI of 83 and CIE values of 0.29, 0.31, with a correlated color temperature of 9433 K. This accomplishment was further underscored by a luminous efficacy of radiation (LER) at 288 lm W⁻¹, solidifying the role of PhAn as a key contributor to efficient and visually appealing white light emission. Moreover, the integration of the organic fluorophores with near-UV chips enhanced their practical application. White light was generated by physically mixing the fluorophores and integrating them with an Eu(III) phosphor in an equimolar ratio, offering a dual solution to the fabrication of efficient white LEDs and advanced methods for the detection of hazardous materials. Additionally, the designed fluorophores revealed a Stern–Volmer quenching constant of 9.09 × 10⁻² M⁻¹ and a detection limit of 3.46 ppb, showing the ability to detect picric acid using fluorescence, DFT analysis, and ¹H NMR spectroscopy. Furthermore, a thorough study of single crystals of all the synthesized fluorophores was conducted.