Micelle Assisted Multi‐Step Energy Relay in a Blend of Fluorophores as a Potential Light Harvesting System

Abstract We report a pH‐responsive system comprising three pH responsive fluorophores, 7‐Hydroxy coumarin (7HC), Fluorescein (Flu), and Rhodamine B (RhB) wherein an efficient two‐step Förster Resonance Energy Transfer (FRET) process is facilitated. Upon excitation of 7HC, energy is sequentially transferred from 7HC (primary donor) to Flu (primary acceptor) and then to RhB (secondary acceptor). The FRET processes were studied at pH 7 and 12 in the presence of surfactants: cationic Tetradecyltrimethylammonium bromide (TTAB), anionic Sodium Dodecyl Sulfate (SDS), and neutral polyoxyethylene[4] lauryl ether (Brij 30). Differences in FRET efficiencies across surfactant media were interpreted by analyzing the solubilization sites of the fluorophores using UV‐Visible and fluorescence spectroscopy. The pH‐dependence of the FRET acted as an ON‐OFF switch, showing higher efficiency in alkaline media. Among the surfactant systems, the two‐step FRET operated most efficiently in alkaline TTAB micelles, with efficiencies reaching up to 50 % for 7HC to Flu (FRET‐1), 30 % for Flu to RhB (FRET‐2), and 23 % for the overall transfer. At a donor‐to‐acceptor ratio of 1000/80/80, energy transfer efficiencies touched 74 % for FRET‐1 and 84 % for FRET‐2. This highlights TTAB micelles as promising scaffolds for efficient multi‐step FRET‐based artificial light‐harvesting systems.