Pentacenes

Figure Cl.5.2. Fluorescence excitation spectra (cps = counts per second) of pentacene in /i-teriDhenyl at 1.5 K. (A) Broad scan of the inhomogeneously broadened electronic origin. The spikes are repeatable features each due to a different single molecule. The laser detuning is relative to the line centre at 592.321 nm. (B) Expansion of a 2 GHz region of this scan showing several single molecules. (C) Low-power scan of a single molecule at 592.407 nm showing the lifetime-limited width of 7.8 MHz and a Lorentzian fit. Reprinted with pennission from Moemer [198]. Copyright 1994 American Association for the Advancement of Science.

Line shifts as a function of pressure have been studied for pentacene and terrylene in /i-teriDhenyl [98, 99]. Botli exhibited linear and reversible spectral red shifts witli increasing pressure. Modest variations (factors of 1.3-1.6) in tlie pressure shifts among molecules were attributed to slightly different local environments. 

The polarization properties of single-molecule fluorescence excitation spectra have been explored and utilized to detennine botli tlie molecular transition dipole moment orientation and tlie deptli of single pentacene molecules in a /7-teriDhenyl crystal, taking into account tlie rotation of tlie polarization of tlie excitation light by tlie birefringent... 

Ambrose W P, Basche T and Moerner W E 1991 Detection and spectroscopy of single pentacene molecules in a p-terphenyl crystal by means of fluorescence excitation J. Phys. Chem 95 7150-63... 

Reilly P D and Skinner J L 1995 Spectral diffusion of individual pentacene molecules in p-terphenyl crystal theoretical model and analysis of experimental data J. Phys. Chem 102 1540-52... 

Wild U P, Guttler F, Pirotta M and Renn A 1992 Single molecule spectroscopy stark effect of pentacene in p-terphenyl Chem. Phys. Lett. 193 451-5... 

Guttler F, Croci M, Renn A and Wild U P 1996 Single molecule polarization spectroscopy pentacene in p-terphenyl Chem. Phys. 211 421-30... 

Tchenio P, Myers A B and Moerner W E 1993 Dispersed fluorescence spectra of single molecules of pentacene in p-terphenyl J. Chem. Phys. 97 2491-3... 

Fleury L, Tamarat P, Lounis B, Bernard J and Orrit M 1995 Fluorescence spectra of single pentacene molecules in p-terphenyl at 1.7 K Chem. Phys. Lett. 236 87-95... 

Much of our knowledge of the frequency dependence of VER rates in polyatomic molecules stems from low-temperature studies of molecular crystals [2] such as pentacene (PTC 221 4) guest molecules in a crystalline naphthalene (N C,., H ) host. In naphthalene, the phonon cut-off frequency is -180 cm [97]. At low temperature,... 

Figure C3.5.10. Frequency-dependent vibronic relaxation data for pentacene (PTC) in naphthalene (N) crystals at 1.5 K. (a) Vibrational echoes are used to measure VER lifetimes (from [99]). The lifetimes are shorter in regime I, longer in regime II, and become shorter again in regime III. (b) Two-colour pump-probe experiments are used to measure vibrational cooling (return to the ground state) from [1021.

Chang T-C and DIott D D 1989 Vibrational cooling in large molecular systems pentacene in naphthalene J. Chem. Phys. 90 3590-602... 

It is interesting to note that recent evidence shows that even extra-terrestrially formed hydrocarbons can reach the Earth. The Earth continues to receive some 40,000 tons of interplanetary dust every year. Mass-spectrometric analysis has revealed the presence of hydrocarbons attached to these dust particles, including polycyclic aromatics such as phenanthrene, chrysene, pyrene, benzopyrene, and pentacene of extraterrestrial origin indicated by anomalous isotopic ratios. 

Zone refining purified naphthalene from anthracene, 2,4-dinitrophenylhydrazine, methyl violet, benzoic acid, methyl red, chrysene, pentacene and indoline. 

This trend is revealed, for example, by the rates of Diels-Alder addition reactions of anthracene, naphthacene, and pentacene, in which three, four, and five rings, respectively are linearly fused. The rate data are shown in Table 9.3. The same trend can be seen in the activation energy and the resonance energy gained when cycloreversion of the adducts 9-12 yields the aromatic compoimd, as shown in Scheme 9.3. 

The pentacene is formed by five aligned condensed benzene rings (Fig. 14-18). 

A most remarkable set of data was reported by Nelson and coworkers [96] on pentacene. Three devices, made within the same run, were presented. The data art shown in Figure 14-26. 

Figure 11.7 Scanning electron micrograph of pentacene fibers prepared by dewetting of a hot trichlorobenzene solution using the roller apparatus. The fibers are aligned along the rolling direction (reprinted with permission from Ref 71). The scale bar is 5 pm.

T. T. M. (2004) Effect of impurities on the mobility of single crystal pentacene. Appl. Phys. Lett., 84, 3061-3063. 

Minakata, T. and Natsume, Y. (2005) Direct formation of pentacene thin films by solution process. Syn. Met., 153, 1—4. 

Kai, K. and Karthaus, O. (2007) Growth of unidirectionally oriented pentacene nanofibers by a roller method . e-J. Surf. Sci. Nanotechnol, 5, 103-105. 

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