Abstract
We report time-resolved spectral hole-burning experiments on bacteriochlorophyll-a (BChl-a) doped into the glass triethylamine (TEA) at ambient pressure (Δp=0) and at a pressure of Δp=3.4 GPa. We observe a number of remarkable effects: (a) from the change in the temperature dependence of the “effective” optical homogeneous linewidth Γ′hom, we conclude that local order is introduced in TEA under high pressure; (b) from the change in the time dependence of Γ′hom, we conclude that spectral diffusion is induced by “downhill” energy transfer among BChl-a molecules (at a concentration of c∼5×10−4 M) within the S1↔S0 0-0 band, both at ambient and high pressure; and (c) from the wavelength dependence of Γ′hom, we conclude that an energy barrier (ΔE∼135 cm−1 at Δp=0, and ΔE∼70 cm−1 at Δp=3.4 GPa
) has to be crossed in order to excite two-level systems (TLSs) of the TEA host which, subsequently, leads to spectral diffusion. We present a qualitative molecular model for the interpretation of these effects.