Multi-dimensional, light-controlled switch of fluorescence resonance energy transfer based on orderly assembly of 0D dye@micro-micelles and 2D ultrathin-layered nanosheets

Fluorescence resonance energy transfer (FRET) systems have broad applications in visual detection, intelligent materials, and biological imaging, all of which favor the transmission of light through multiple dimensions and in diverse directions. Herein, we have demonstrated multi-dimensional (0D and 2D) FRET within a multi-layer ultrathin film (UTF) by employing a layer-by-layer (LBL) assembly technique. The anionic block copolymer micelle poly(tert-butyl acrylate-co-ethyl acrylate-co-methacrylic acid) (PTBEM) is chosen as a molecular carrier for the incorporation of bis(8-hydroxyquinolate) zinc (Znq₂) and open-ring merocyanine (MC) (denoted as (Znq₂/MC)@PTBEM). Alternatively, electrostatic assembly is performed with cationic layered double hydroxide (LDH) nanosheets (denoted as [(Znq₂/MC)@PTBEM/LDH]_n). This [(Znq₂/MC)@PTBEM/LDH]_n system offers a multi-dimensional propagation medium and ensures that the FRET donor and acceptor are located within their F?rster radii in each direction. The system demonstrates a FRET process that can be switched via alternating ultraviolet/visible (UV/vis) irradiation, with tunable blue–green/red fluorescence, resulting in a FRET efficiency as high as 81.7%. It is expected that this assembly method, which uses 0D micelles on a 2D layered material, can be extended to other systems for further development of multi-dimensional FRET.