Light Induced Single Molecule Frequency Shift.

A light induced frequency shift of the 0-0 line was measured in two-photon excitation spectra of single diphenyloctatetraene molecules doped in a crystal matrix. The shifts were proportional to the laser power with a slope of about 600 MHzyW when the laser beam of about 300 mW power was focused to a diameter of 2 mm. Significantly, the observed line broadenings were an order of magnitude smaller than the shifts. The effect is ascribed mainly to a “fast” energy exchange between a local vibration and thermal phonons created by the third harmonic C-H band absorption in the matrix, and partially to an ac Stark shift. [S0031-9007(96)02047-9]