Terrylene Molecules Research Articles

Single molecule spectroscopy of terrylene in n-alkane mixtures

To answer the question of whether special Shpol'skii guest–host combinations which exhibit well-defined trapping sites are essential for single molecule spectroscopy, we have reinvestigated at high-resolution the fluorescence of single molecules of terrylene. Our experiments have demonstrated that similar to the well-known terrylene– n-decane “Shpol'skii” system, spectra of comparable quality and with lifetime-limited linewidths of about 50 MHz can also be obtained in several mixtures of alkanes. In the light of these results we then discuss the prospects for single molecule (or single ion) spectroscopy in rare gas matrices.

Pressure effects on single-molecule spectra of terrylene in hexadecane

The effect of hydrostatic pressure on single-molecule spectra has been studied at 4.4 K for 48 terrylene molecules in a Shpol'skii matrix, hexadecane. From the average rate of the pressure shift of the single-molecule lines, the low-temperature compressibility of hexadecane has been estimated at 0.037 GPa −1. The shift parameter has been found to be dispersed more widely in hexadecane compared with p-terphenyl. 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 terrylene in a Shpol'skii matrix.

Low-Temperature Confocal Microscopy on Individual Molecules near a Surface

The spectral behavior of single terrylene molecules at a hexadecane−silica interface structure is studied. Different sample preparation techniques indicate that molecules close to a silica substrate in a hexadecane matrix are subject to additional dephasing or spectral diffusion. The temperature activation of the homogeneous line width of these molecules shows much reduced activation energies as compared to those of molecules in bulk hexadecane. These low-lying activation energies may be attributed to surface phonon states or local phonon modes particular to the interface structure. With the aid of a low-temperature scanning confocal microscope, the distance of single terrylene molecules to the silica surface can be measured with a precision of 60 nm. A drastic increase of the homogeneous line width for molecules with distances less than 150 nm to the silica surface is found.

Excitation of a single molecule on the surface of a spherical microcavity

We use the optical resonance of a spherical microcavity (quality factor ∼106) to excite a single molecule. By attaching a p-terphenyl crystal doped with pentacene and terrylene molecules to a dielectric sphere, we detect individual molecules excited by the near field of the cavity. A low-temperature optical microscope is utilized to image the emission from the single molecule, determine its position on the sphere surface, and measure its absorption linewidth. These results demonstrate the feasibility of single-molecule cavity quantum electrodynamics.

Single molecules observed by immersion mirror objective. The orientation of terrylene molecules via the direction of its transition dipole moment

Fluorescence from single molecules of terrylene in a Shpol'skii matrix (n-hexadecane or n-dodecane) was detected with an immersion mirror objective. An analysis of fluorescence intensity distribution outside the image plane has been performed according to a method presented earlier (preceding Letter). Spatial orientations of a long molecular axis for several individual terrylene molecules have been found. One of the angles from the pair describing spatial orientation was found to match the value available from routine polarisation experiments.

Single-molecule optical switching of terrylene in p-terphenyl

The controlled manipulation and switching of single atoms and molecules raise the prospect of ultra-high-density data storage. Switching by motion of a single atom has been reported1, and techniques of single-molecule optical detection and spectroscopy2 in the condensed phase have been refined to a degree that allows the modification of the absorption properties of a single chromophore3. Light-induced jumps in single-molecule excitation frequencies have been reported3,4,5, but in none of these cases could the process be controlled: the jumps varied from molecule to molecule, they were interrupted by spontaneous jumps, and the new excitation frequencies could not be identified unambiguously. Here we report light-induced reversible frequency jumps ofsingle molecules of the aromatic hydrocarbon terrylene embedded in a particular site of a p-terphenyl host crystal6 at temperatures of around 2 K. The changes in absorption frequency for different terrylene molecules were identical (within 0.5%) for all samples studied. Thus we were able to switch single-molecule absorption lines in a controlled way between well-defined frequency positions.

Photophysical properties of single terrylene molecules in Shpolskii matrices

We studied distributions of line widths of terrylene in n-alkanes. In dodecane the line broadening is caused by fast dephasing. The additional broadening in hexadecane is attributed to spectral diffusion.

Excitation induced frequency shifts of single molecules

We have developed an experimental scheme to observe frequency shifts of single molecule absorption lines induced by a controlled manipulation in the surroundings in the solid state at low temperatures. In a mixture of terrylene and triphenylene in the matrix n-octane many single terrylene molecules are observed in parallel with a fluorescence microscope while triphenylene molecules are excited to their long-living triplet state. Frequency shifts are induced upon excitation and relaxation of triphenylene, resulting in increased spectral dynamics of terrylene molecules during the relaxation period.

Single-Molecule Spectroscopy and Persistent Hole Burning of Terrylene in p-Terphenyl: External-Field Effects

Abstract Fluorescence excitation spectra of single terrylene molecules in p-terphenyl crystals were investigated at low temperatures. The line shifts due to hydrostatic pressure and external electric fields were measured, with the electric field strength oriented either parallel or perpendicular to the k vector of the laser light. A linear Stark effect was found for most molecules, indicating local environments of low symmetry. In sites X1 and X3 (and XY, a photoproduct state), spectral hole burning was observed. Whereas the holes are stable in sites X1 and XY, they decay with a time constant of some minutes in X3. Pressure experiments were performed on the stable hole spectra in sites X1 and XY. In weakly doped samples, holes composed of very few molecular lines were generated with halfwidths distinctly narrower than twice the homogeneous linewidth.

Single Molecule Spectroscopy: Terrylene in the Polymorphic Matrix Benzophenone

Abstract We report a new matrix for single molecule spectroscopy: terrylene doped into benzophenone. The peculiarity of this matrix consists of its polymorphism. Single terrylene molecules were detected in the polycrystalline phase of the benzophenone host. In the glassy phase of the matrix, single molecules were not resolved. An upper limit for the homogeneous width of the terrylene molecules in the glassy phase was obtained from hole-burning experiments. Total luminescence spectra in both amorphous and crystalline phase of bulk samples were measured.

Pressure Effects on Single Molecules of Terrylene in p-Terphenyl

Abstract Fluorescence excitation spectra of single molecules and persistent holes of terrylene in p-terphenyl crystals were investigated under hydrostatic pressure up to 10510 hPa. Single-molecule lines could be observed around all four inhomogeneous bands X1 to X4. They showed a linear and reversible pressure shift between -0.92 MHz/hPa and -1.55 MHz/hPa with no clear differences between the inhomogeneous bands. The relative fluctuations of the pressure shift parameter between different molecules are larger than for pentacene in p-terphenyl which indicates a less well-ordered local environment of the dopant molecules. Persistent hole-burning was possible in the bands X1 and X3 of the same samples in which single-molecule lines were observed. The pressure shift of the hole spectra (which are close to the band center) is smaller than the shift of the single-molecule lines (in the wings of the band). Hence, the molecules seem to feel different local compressibilities.

Measurement of Optical Dephasing of a Single Terrylene Molecule with Nanosecond Time Resolution

Measurement of Optical Dephasing of a Single Terrylene Molecule with Nanosecond Time Resolution

Pump-Probe Experiments with a Single Molecule: ac-Stark Effect and Nonlinear Optical Response.

We have measured the ac-Stark effect on single terrylene molecules in $p$-terphenyl crystals at superfluid helium temperatures. With the pump beam far enough from resonance, the molecular transition shifts as expected, i.e., proportional to the pump intensity and to the inverse pump detuning. Experiments closer to resonance with stronger beams show Autler-Townes-like structures that can be well reproduced by means of Bloch equations with two intense laser fields. These experiments are a demonstration of nonlinear optical effects with the localized electronic states of a single molecule trapped in a solid.

Pressure effects on single molecules of terrylene in p-terphenyl

The hydrostatic-pressure shift of the zero-phonon lines of single terrylene molecules in a p-terphenyl host crystal was measured at 1.6 K. We found four inhomogeneous absorption bands of the terrylene molecules in p-terphenyl with inhomogeneous widths between 15 and 33 GHz, corresponding to four crystal sites, and we measured the pressure shift of single molecules in the sites X 2, X 3, and X 4. All the molecules investigated (35 in total) exhibited a linear and reversible red-shift with increasing pressure, with magnitudes between −0.92 and −1.48 MHz/hPa. The pressure shift parameter was found to be independent of the spectral position of the molecules.

Single molecule spectroscopy: maximum emission rate and saturation intensity

We consider the collection efficiency for photons emitted by a single molecule in a solid excited by monochromatic light at low temperature, which depends upon the dipole radiation pattern, the orientation of the emission dipole, total internal reflection, and the numerical aperture of the collecting optics. By using the complete expression for the collection efficiency and varying the collection angle, we have determined the orientation of the dipole of a single terrylene molecule in hexadecane to be almost perpendicular to the substrate. By using saturation data we find that the angle between the optical axis of the collection paraboloid and the emission dipole moment is 16±6°. We estimate that the true saturation intensity of terrylene (for dipole moment parallel to the electric field of the light) is about (80±30) mW/cm 2 and that the ratio of the intersystem crossing rate to the total decay rate of the triplet state is about 3.3±1.2.

Direct spectroscopic observation of quantum jumps of a single molecule

BOHR'S notion of quantum jumps between electronic states of an excited atom has now been demonstrated experimentally for single ions confined in radio-frequency traps and interacting with a driving laser field1–3. In these experiments the fluorescence of a strongly allowed transition was shown to cease abruptly when the ion jumped into a metastable state which was coupled to the common electronic ground state by a weak radiative transition. But attempts to monitor quantum jumps of single molecules have been hampered by the fact that the lifetime of the metastable triplet state was too short in relation to the photon detection rate. By using a system with favourable photophysical parameters—terrylene doped into p-terphenyl crystals4—we have now been able to observe directly quantum jumps between electronic states of single terrylene molecules. In contrast to single atoms, here the quantum jumps occur as non-radiative transitions between states of different multiplicity, and are manifested as interruptions of the fluorescence signal. These results demonstrate how single-molecule spectros-copy can reveal truly quantum-mechanical effects in large polyatomic molecules.

Single molecule lines and spectral hole burning of terrylene in different matrices

We observe fluorescence excitation lines of single terrylene molecules in three new polymer matrices (polyvinylbutyral, polymethylmethacrylate, and polystyrene) and in two crystals, n-hexadecane (polycrystalline Shpol’skii matrix) and anthracene single crystal. We also burn persistent spectral holes in bulk samples of these solutions for comparison to single molecule lines. In all matrices where hole burning is efficient enough, we find good agreement between the average width determined from the distribution of single molecules’ linewidths and the homogeneous width deduced from spectral holes, which demonstrates the consistency and complementarity of the two techniques.

Terrylene in p-terphenyl: a novel single crystalline system for single molecule spectroscopy at low temperatures

Terrylene in p-terphenyl represents a promising novel single crystalline system for optical spectroscopy of single impurity molecules at low temperatures. The optical spectra of terrylene in p-terphenyl show four origins in absorption and emission, indicating four crystalline sites. In one of the sites saturated fluorescence count rates of up to 600000 s −1 were measured for single terrylene molecules. From a measurement of the fluorescence autocorrelation function for single terrylene molecules we could determine the populating and depopulating rates of the triplet state. Using the very small populating rate the triplet quantum yield was calculated to be only ~ 10 −5.

Optical Probing of Single Molecules of Terrylene in a Shpol'kii Matrix: A Two-State Single-Molecule Switch

We report fluorescence excitation spectra of individual impurity molecules in a new system: terrylene in a Shpol'skii matrix of hexadecan, Studies of optical incoherent saturation, fluorescence microscope images, 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 saturation intensity is near 1 W/cm(2), and the peak detected count rate can reach 11000 counts per second. Most single molecules either are stable or require many minutes of irradiation before the resonance frequency changes suddenly, but some show spectral changes on a time scale of seconds. Since higher laser power increases the average rate of frequency shifts, this effect represents a light-driven change in the local environment analogous to nonphotochemical hole-burning in large ensembles. Several two-state molecules have been observed, and a preliminary characterization of this light-driven ''molecular switch'' has been completed. Multistate behavior also occurs. This work demonstrates that Shpol'skii matrices should provide fertile ground for the generation of a large number of new materials in which single-molecule spectra can be obtained.

Vivronic spectroscopy of single molecules: Exploring electronic-vibrational frequency correlations within an inhomogeneous distribution

Vibrationally resolved dispersed fluorescence spectra have been obtained from single molecules of terrylene in polyethylene at 1.5 K using excitation wavelengths from 577 to 566 nm, spanning both sides of the inhomogeneously broadened electronic origin. The spectra of different molecules exhibit significantly different frequency and intensity patterns. There is a weak overall correlation between ground state vibrational frequencies and wavelength of the electronic origin, with the redder-absorbing molecules tending to have higher vibrational frequencies. The red-shifted absorbers may reside in smaller cavities in the matrix, thus experiencing both strongerh dispersive interactions and more severe atom-atom repulsions.