Photophysical Properties of Chlorophyll <i>a</i> in Triblock Copolymers Micelle: A Combined Fluorescence Spectroscopy and Molecular Dynamics Simulation Study

This study demonstrates the interaction of a green pigment, Chlorophyll <i>a</i> (Chl <i>a</i>), in the microenvironments of two different pluronic triblock copolymers (TBPs), P123 and F127, upon encapsulation into polymeric micelle. TBP micelles are nontoxic and quite efficient for the stabilization of this particular plant pigment, which is poorly soluble in water. In present investigation, experimental analysis (absorption, fluorescence spectroscopy, including lifetime, and FCS) along with MD simulations study was performed to explore the molecular details and interaction mechanism of Chl <i>a</i> with P123 and F127 micelles. The emission intensity along with fluorescence quantum yield (Φ), fluorescence lifetime (τ_<i>f</i>), and diffusion time (τ_<i>D</i>) was found to be enhanced, which demonstrates the encapsulation of pigment molecules in polymeric micelles. The binding constant was determined by fluorescence technique, which further validates the binding phenomenon and location of Chl <i>a</i> in micellar aggregates. Different simulation snapshots of Chl <i>a</i> encapsulation and time-resolved center-of-mass (COM) analysis demonstrate stable localization of Chl <i>a</i> within the hydrophobic core region. Greater hydrophobicity of P123 micelles compared to F127 drives stronger encapsulation of Chl <i>a</i>, as obtained from the experimental observations and MD simulation study. Overall results indicate that the tuning of the photophysics of Chl <i>a</i> is due to its strong hydrophobic interaction with the hydrophobic poly(propylene oxide) (PPO) units of both micelles. These findings are significant in designing future drug delivery systems that preserve the photosensitizer's characteristics for photodynamic therapy.