Ultrafast Excited-State Deactivation of the Bacterial Pigment Violacein


Ashley A. Beckstead, Yuyuan Zhang, Jonathan K. Hilmer, Heidi J. Smith, Emily Bermel, Christine M. Foreman, Bern Kohler


Journal of Physical Chemistry B


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 x 10(-4), and femtosecond transient absorption measurements reveal excited-state lifetimes of 3.2 +/- 0.2 and 4.6 +/- 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 interring bond leads to a conical intersection with the ground state.



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