We then follow this discussion on the broadening of the hole as a function of time (spectral diffusion). We show that the amount of spectral SHP099 diffusion depends on the size of the photosynthetic complex studied. Further, we demonstrate that, in addition to the hole width, the hole depth as a function of wavelength can also yield relevant information that is otherwise hidden under the broad absorption bands. Data reviewed proves the existence of ‘traps’ for energy transfer
in photosystem II (PSII) sub-core complexes of higher plants. The final example Stem Cells inhibitor shows how we uncovered the lowest k = 0 exciton states hidden under the B850 band of LH2 complexes, and how their spectral distributions could be determined. To our knowledge, HB is the only technique that is able to uncover small, hidden spectral distributions characterized by specific dynamics. Homogeneous
linewidths, optical dephasing and spectral diffusion Absorption and emission bands of pigment–protein complexes and organic molecules dissolved in solvents or polymers are generally very broad (typically a few 100 cm−1, even at liquid-He temperatures), as compared to those found in crystalline systems (of a few cm−1). Such large widths are caused by the slightly different environments of the individual chromophores within the disordered host (the IWP-2 solubility dmso protein or glass at low temperature), leading Phospholipase D1 to a broad statistical distribution of the electronic transition energies
and, therefore, to a wide Gaussian profile with an inhomogeneous width Γinh (Creemers and Völker 2000; Völker 1989a, b, and references therein). Information on the dynamics of the excited state of the system is contained in the homogeneous linewidth Γhom of the electronic transition of the individual chromophores. Since Γhom is usually a factor of 103–105 times smaller than Γinh (Völker 1989a, b), the homogeneous line is buried in the inhomogeneously broadened band. To obtain the value of Γhom, laser techniques must be used, either in the time domain, such as photon echoes (Agarwal et al. 2002; Fidder and Wiersma 1993; Fidder et al. 1998; Hesselink and Wiersma 1980, 1983; Jimenez et al. 1997; Lampoura et al. 2000; Narasimhan et al. 1988; Thorn-Leeson and Wiersma 1995; Thorn-Leeson et al. 1997; Wiersma and Duppen 1987; Yang and Fleming 1999), or in the frequency domain, such as FLN, HB and SM (for references, see above). The lineshape of a homogeneously broadened electronic transition is usually Lorentzian; it is the Fourier-transform of an exponential decay function.