Pentacene first example

The first example of a pentacene precursor was a tetrachlorocyclohexadiene adduct prepared by the Mullen group (Figure 5.3.9a) [47]. This derivative is soluble in dichloromethane and forms good films by spin-coating. After deposition, the pentacene film is formed by a thermally activated retro Diels-Alder reaction expelling tetrachlorobenzene as the by-product. The hole mobilities of OFETs prepared from these pentacene precursors depended greatly on the annealing temperature... 

The first SMS experiments in 1989 utilized either of two powerful doublemodulation FM absorption techniques, laser frequency-modulation with Stark secondary modulation (FM-Stark) or frequency-modulation with ultrasonic strain secondary modulation (FM-US) [3,26]. The secondary modulation was required in order to remove the effects of residual amplitude modulation produced by the imperfect phase modulator. In contrast to fluorescence methods, Rayleigh and Raman scattering were unimportant. Figure 2.3B (specifically trace d) shows examples of the optical absorption spectrum from a single molecule of pentacene in p-terphenyl using the FM-Stark method. 

While not completely accurate, the PFEO model provides an estimate of the first level excitation energy and explains the trend in HOMO-LUMO gap. As the molecule increases in size the HOMO-LUMO gap decreases in magnitude and it becomes easier to generate an excited state. Technologically this has some ramifications for example, hexacene s very small HOMO-LUMO gap makes its electrons easy to excite. The material is easily oxidized in air and unsuitable for air stable transistors. The HOMO and LUMO surfaces for pentacene are shown in Fig. 2.8. It is clear that the wavefunction indeed travels around the perimeter of the molecule and this distance is a significant determiner of the electronic properties of the material. 

Fig. 1 A timeline of advances in scanning probe microscopy spanning the publication of the first STM images of the Si(l 11)-(7 x 7) surface in 1983, through Eigler et al. s pioneering atom manipulation work in the early 90s, to the more recent examples of NC-AFM manipulation of atoms on silicon and metal surfaces, the acquisition of images of pentacene with chemical bond resolution (2009) and, most recently, the mapping of molecular force fields. Image courtesy of Samuel Jarvis.

Fig. 1. The first row shows examples of natural transannular peroxides ascari-dole and a-phillandrene peroxide. The former can be obtained from terpene by diensynthesis with Oj and with chlorophyll or eosin as a photosensitizer. The second row shows sterol peroxide (Windaus and Brunken, 1928) and pentacene (Dufraisse, 1939). The last row illustrates the reversibility of oxygen addition in some cases (Dufraisse and Etienne, 193S).

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