Enhancing electrofluorochromic efficiency through C30H31N6+-sensitized layer-by-layer polyoxometalate films

Abstract

The inability to use organic cations in layer-by-layer (LBL) films stringently limits the efficiencies of most LBL films, such as luminescence-switched lanthanide-containing polyoxometalate (Ln-POM) functional composite films. Here, selecting luminescent organic cations such as C30H31N6+ (JGB) to facilitate energy transfer is proposed as a strategy to alleviate the fluorescence resonance energy transfer (FRET) efficiency problem. In typical Ln-POM ([ErSiW9/JGB]9) films, the FRET process occurs from luminescent species to electro-reduced POM, resulting in fluorescence quenching. In contrast, the organic cations (C30H31N6+) are able to transfer the harvested energy to the luminescent species (Sm), entailing a ~677-fold improvement over the overall luminescence efficiencies of [SmSiW9/JGB]9 films. Incorporating C30H31N6+ into the SmSiW9-contained LBL films elevates the electrofluorochromic efficiency to 93%, enhancing the power conversion efficiency by about 21.7%. The FRET contribution in [SmSiW9/JGB]9 was significantly higher than that in the [ErSiW9/JGB]9 films because of the structural change of SmSiW9 in the multilayer film. This strategy has immediate implications for using fluorescent organic cations to improve the performance of luminescence-switched POM functional devices.