OPTICAL PROBING OF SINGLE MOLECULES OF TERRYLENE IN A SHPOLSKII MATRIX - A 2-STATE SINGLE-MOLECULE SWITCH

We report fluorescence excitation spectra of individual impurity molec ules in a new system: terrylene in a Shpol'skii matrix of hexadecan, S tudies of optical incoherent saturation, fluorescence microscope image s, and resonance frequency changes are reported for the 0-0 electronic transition at 1.7 K. For four stable molecules, the low-power optical line width at 1.7 K is 40 +/- 2 MHz full width at half-maximum, the s aturation intensity is near 1 W/cm(2), and the peak detected count rat e can reach 11000 counts per second. Most single molecules either are stable or require many minutes of irradiation before the resonance fre quency changes suddenly, but some show spectral changes on a time scal e of seconds. Since higher laser power increases the average rate of f requency shifts, this effect represents a light-driven change in the l ocal environment analogous to nonphotochemical hole-burning in large e nsembles. Several two-state molecules have been observed, and a prelim inary characterization of this light-driven ''molecular switch'' has b een completed. Multistate behavior also occurs. This work demonstrates that Shpol'skii matrices should provide fertile ground for the genera tion of a large number of new materials in which single-molecule spect ra can be obtained.