Ultrafast Excited-State Deactivation of the Bacterial Pigment Violacein

Abstract

The photophysical properties of the natural pigment violacein extracted from an Antarctic organism adapted to high exposure levels of UV radiation were measured in a combined steady-state and time-resolved spectroscopic study for the first time. In the low-viscosity solvents methanol and acetone, violacein exhibits low fluorescence quantum yields on the order of 1 × 10, and femtosecond transient absorption measurements reveal excited-state lifetimes of 3.2 ± 0.2 and 4.5 ± 0.2 ps in methanol and acetone, respectively. As solvent viscosity is increased, both the fluorescence quantum yield and excited-state lifetime of this intensely colored pigment increase dramatically, and stimulated emission decays 30-fold more slowly in glycerol than in methanol at room temperature. Excited-state deactivation is suggested to occur via a molecular-rotor mechanism in which torsion about an interring bond leads to a conical intersection with the ground state.

Terrestrial Microorganisms: Cell Factories of Bioactive Molecules with Skin Protecting Applications

“…Known to possess antibacterial effects against Staphylococcus aureus and other Gram-positive pathogens, violacein can also act as a photo-protective agent against UV irradiation. This compound absorbs at visible wavelengths and presents a broad absorption band extended out to 700 nm [69]. When used as an additive in commercial sunscreens (4% w / w violacein), the SPFs increased by 10–22%.…”