Terrylene in p-terphenyl

Fluorescence spectra of single terrylene molecules were also recorded recently in the crystalline matrix of p-terphenyl [29] using again a similar setup as shown in Fig. 8. Most of the observed vibrational frequencies coincide with those of terrylene in polyethylene with the exception of small frequency shifts. In Fig. 11 the fluorescence spectrum of a single terrylene molecule in site Xz [29], which is the most photostable site, is displayed. The most important feature is the appearance of two lines of similar intensity at 244 and 256 cm, respectively. This doublet has not to be confused with type 1 and type 2 spectra in terrylene/polyethylene as discussed in the preceding section because those stem from different molecules. In contrast, in the p-terphenyl crystal the doublet around 250 cm is an inherent property of a single absorber, a fact which also can be deduced from bulk spectra through the appearance of the combination band at 500 cm.  

According to the theoretical study discussed above, the intense low frequency vibration around 250 cm is attributed to a long axis stretch of the whole molecule. The authors of [38] also studied the influence of various possible static distortions of the terrylene molecule on its vibrational structure. A boat or butterfly distortion about the short axis such that the planes of the terminal naphthalenes make a 

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Kummer S, Basche T and Brauchle C 1994 Terrylene in p-terphenyl a novel single crystalline system for single molecule spectroscopy at low temperatures Chem. Phys. Lett. 229 309-16... 

Muller A, Richter W and Kador L 1995 Pressure effects on single molecules of terrylene in p-terphenyl Chem. Phys. Lett. 241 547-54... 

Kulzer F, Kummer S, Matzke R, Brauchle C and Basche T 1997 Single-molecule optical switching of terrylene in p-terphenyl Nature 387 688-91... 

Kulzer F, Koberling F, Christ T, Mews A and Basche T 1999 Terrylene in p-terphenyl single-molecule experiments at... 

The absorption spectra of terrylene in the gas phase are not known. Using the compressibility calculated from the pentacene data, the solvent shift of terrylene in p-terphenyl is estimated to be Avs = 2345 + 411 cm and therefore its vacuum absorption wavelength should be 509 11 nm. The larger solvent and pressure shifts found for terrylene as compared to pentacene seem reasonable, since terrylene is bigger and therefore expected to exhibit larger polarizabilities in its ground and excited state. 

Study of the shape of the correlation function in the ns time regime has been used to determine both T and Ti for a single terrylene molecule in p-terphenyl [87]. 

Figure 3. Fluorescence excitation spectra of a single terrylene molecule in p-terphenyl (site X2) at 2 and 5 K. Note the broadening and the shift of the optical line at the higher temperature.

Figure 5. Temperature dependence of the optical linewidth and lineshift for a single terrylene molecule in p-terphenyl. Both data sets could be approximated by fitting an activated process (Eq. 4) to the data. The width as well as the shift yield an activation energy of 17 2cm. ...

Figure 11. Fluorescence spectrum of a single terrylene molecule in p-terphenyl in site (F = 1.4 K). The accumulation time to record the complete spectrum was 600 seconds. The spectrum is in good agreement with a bulk spectrum of the 2-site.

Figure 12. Fluorescence counts detected for a single terrylene molecule in p-terphenyl (site Xi) as a function of time. The quantum jumps are clearly visible as discrete intenuptions of the fluorescence. The sample was cooled to 1.4 K and the molecule was excited with an (free space) intensity of 62.5 W/cm. (b), a I s section of a 26.8 s data set, (a), a region covering 80 ms displayed on a magnified scale.

Using the experimental setup (Fig. 15) described in the last paragraph, the fluorescence intensity correlation function was measured for a single terrylene molecule in p-terphenyl over nine orders of magnitude in time by the authors group [27]. The experimental trace in Fig. 16 clearly displays the characteristic features of photon antibunching and photon bunching. The onset of Rabi oscillations is clearly visible, too. We now want to discuss separately these three effects for different systems and what can be learned from such measurements. 

In Section 1.2.2.2 it was shown that the optical linewidth of a single terrylene molecule in p-terphenyl is broadened by librational mode induced pure optical dephasing (Tl-processes) when the temperature is increased. In Fig. 18, is... 

The decay of the correlation function for a single terrylene molecule in p-terphenyl due to photon bunching was already presented in Fig. 16. In this case a biexponential decay - not easily visible in Fig. 16 - is observed because two of the sublevels are sufficiently distinct with regard to their kinetics (see Section 1.2.4.2). The measurements and the analysis of the experimental data to determine the population and depopulation rates were done in analogy to the previous description for pentacene in p-terphenyl. The ISC rates were in fairly good agreement with those determined from quantum jump measurements discussed in Section 1.2.4.2. In contrast to pentacene in p-terphenyl, the terrylene molecules studied so far did not exhibit a large variation of the ISC rates between different molecules [6]. 

Similar spectral dynamics of individual chromophores from repeated fluorescence excitation scans have subsequently been seen in amorphous hosts, for the systems Tr in polyethylene (PE) [14] and tetra-r-butyl-terrylene (TBT) in polyisobutylene (PIB) [15, 16]. In at least one instance [16] the chromophore samples far fewer frequencies than in the case of pentacene in p-terphenyl. The spectral difl usion trajectories are assumed to result from the flipping of those TLSs whose dynamics is slower than the scan time. 

Figure 2. Fluorescence excitation spectrum at 1.4 K of terrylene in a p-terphenyl single crystal in the spectral region of site Xi ( 580.4 nm). The narrow features are the excitation lines of single terrylene molecules. The laser was scanned in 32 seconds over the displayed frequency range at an intensity of 25mW/cm (fromRef.6).

In 2004, the first work was reported directed toward single-pair electronic EET in a dyad built from perylene diimide (PDl) as donor, terrylene diimide (TDl) as acceptor and a p-terphenyl spacer (dyad 1, Pig. 1) as bridging group [1]. Since then, several more single-molecule as well as computational studies on this compound have been carried out to investigate the prevailing energy transfer... 

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