Study of spectral diffusion in a broad time range by single molecule spectroscopy

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The effect of hydrostatic pressure on sing-molecule spectra has been studied at〜4.2 K below the atmospheric pressure for pentacene molecules in p-terphenyl and terrylene molecules in a Shpol'skii matrix, hexadecane. All the lines examined showed linear and reversible shifts without an additional broadening. The shift parameter of the single-molecule spectrum has been found to be much spread in hexadecane compared with p-terphenyl. From the average rate of the red-shift with increasing pressure, the low-temperature compressibility of hexadecane has been estimated at 0.037 GPaィイD1-1ィエD1. The temperature dependence of the linewidth has also been found to be considerably different among individual molecules. These results are ascribed to the presence of various microscopic environments of the guest molecule in a Shpol'skii matrix. Saturation of the emission intensity and the linewidth of each single molecule were observed as function of the intensity of the excitation light. The saturation property was different for each molecule, which is ascribable to different orientation of each molecule. Some emission line showed an abrupt change of the emission intensity. Thus, is was confirmed that the spectral diffusion can be observed even under a slow scanning.