A BODIPY‐Based Molecular Rotor in Giant Unilamellar Vesicles: A Case Study by Polarization‐Resolved Time‐Resolved Emission and Transient Absorption Spectroscopy

Abstract

BODIPY and BODIPY‐derived systems are widely applied as fluorophores and as probes for viscosity detection in solvents and biological media. Their orientational and rotational dynamics in biological media are thus of vital mechanistic importance and extensively investigated. In this contribution, polarization‐resolved confocal microscopy is used to determine the orientation of an amphiphilic BODIPY‐cholesterol derivative in homogeneous giant unilamellar vesicles (GUV) made from 1,2‐dioleoyl‐sn‐glycero‐3‐phosphocholine (DOPC). The BODIPY‐moiety of the molecule is placed near the polar headgroups, and the cholesterol moiety is embedded in the membrane along the acyl chain of the lipids. The rotational relaxation of fluorophore is conventionally investigated by time‐resolved emission anisotropy (TEA); and this method is also used here. However, TEA depends on the emission of the fluorophore and may not be useful to probe rotational dynamics of the non‐emissive triplet states. Thus, we employ femtosecond transient absorption anisotropy (TAA), that relies on the absorption of the molecule to complement the studies of the amphiphilic BODIPY in DCM and GUV. The photoinduced anisotropy of the BODIPY molecule in DCM decays tri‐exponentially, the decay components (sub‐5 ps, 43 ps and 440 ps) of anisotropy are associated with the non‐spherical shape of the BODIPY molecule. However, the anisotropy decay in homogenous GUVs follows a biexponential decay; which arises from the wobbling‐in‐a‐cone motion of the non‐spherical molecule in the high viscous lipid bilayer media. The observations for the BODIPY‐chol molecule in the GUV environment by TAA will extend to the investigation of non‐emissive molecules in cellular environment since GUV structure and size resembles the membrane of a biological cell.

Triplet–Triplet Annihilation Upconverting Liposomes: Mechanistic Insights into the Role of Membranes in Two-Dimensional TTA-UC

“…The lipid membrane is a suitable platform to confine the photosensitizer and annihilator to the same plane assuming both species localize to the same region of the membrane, and that their orientation is conducive to energy transfer. To that end, we first prepared large unilamellar vesicles (LUVs) − (hydrodynamic diameter ∼140 ± 5 nm from DLS) of DOPC and two different giant unilamellar vesicles (GUVs), comprising DOPC only and a ternary phase-separated DOPC:SM (sphingomyelin):Chol (2:2:1). From imaging, GUVs were ∼10–30 μm doped with B2P- and B2PI–perylene pairs.…”

“…Both single and ternary giant unilamellar vesicles (GUVs) were prepared by electroformation using the Vesicle Prep Pro (VPP) (Nanion Technologies, Munich, Germany). 53 Single-phase GUVs comprised a DOPC lipid, and the ternary GUVs were prepared using DOPC, sphingomyelin (SM), and cholesterol in a 2:2:1 molar ratio to a final concentration of 5 mM; this ratio forms phase-separated domains in the GUV. The sensitizer and annihilator molecules were mixed with the lipid stock with a 5088:10:1 lipid:annihilator:sensitizer molar ratio.…”