Nonphotochemical Hole Burning Investigated at the Single-Molecule Level:  Stark Effect Measurements on the Original and Photoproduct State

Abstract

By applying an external electric field, we have studied the dc Stark shifts at the two states of a low-temperature single-molecule optical switch. We observe a reversible change from a mainly quadratic field dependence to a linear field dependence. The data analysis provides the S1−S0 dipole moment and polarizability differences of both the original and photoproduct state. On the basis of these data, a detailed microscopic scenario for the underlying nonphotochemical hole burning mechanism is discussed.

Molecular mechanisms of photo-induced spectral diffusion of single terrylene molecules in p terphenyl

“…Such asymmetry is not observed in the present models, but could be induced in real crystals by the proximity of defects such as domain walls ͑see above͒. On the other hand, the calculated values of ͉␦͉ for the M 3.2 conformation ͑assigned to XY͒ range from 230 mD to 300 mD, in fair agreement with measurements by Kulzer et al, 8,24 which range from 215 mD to 263 mD for 15 out of 16 molecules examined ͑the last value was 89 mD͒.…”

“…Kulzer et al 8 recently measured the Stark effect on single terrylene molecules in p-terphenyl obtaining the surprising results outlined above. The coupled Hartree-Fock calculations on free, planar terrylene yield here a jump in the polarizability parallel to the long axis of ␦␣ ញ ϭ100 Å 3 and a vanishing dipole jump ␦.…”

“…This assignment is now inconsistent with later measurements of the Stark effect ͑shift of the electronic transition frequency in an applied electric field͒ of single molecules in origins X 1 ,X 2 and X 4 . 8 These measurements require that the substitution sites should be centro-symmetric to explain the predominantly quadratic dependence of the frequency shift on the field strength, whereas the di-substitution sites are centro-symmetric only in the high temperature, disordered, monoclinic phase of p-terphenyl. In the latter phase, the central rings of the host molecules undergo rapid ͑picosecond͒ flipping through the mean molecular plane.…”

Optical tracing of multiple charges in single-electron devices

“…The transition frequency is thus very sensitive to the local electric field. For example, a sizable fraction of terrylene molecules in a p-terphenyl crystal exhibit a linear line shift of more than 3 MHz/(kV/m) in response to external electric field [14], despite the centrosymmetry of the terrylene molecule. This anomalously high linear response is induced by the deformation of the molecular orbital in the crystal [15].…”

“…(5) happens to be in the order of unity for the aromatic molecules that are relevant to the subject of this paper. For the exemplary system of terrylene in p-terphenyel [14], this prefactor is 4.8. The narrow linewidth of the molecular transitions, with high quality factors of Q = 10 7 , have a wellknown connection with the small value of the fine structure constant [21,22].…”