Polyacenes

Polyacenes are condensed aromatic molecules such as naphthalene, anthracene, tetracene, and pentacene. The most widely studied is anthracene The use of anthracene as a photoreceptor was first described in Carlson s original patent (1942). Because of its poor physical and mechanical properties and lack of absorption in the visible or near infrared, it is not of practical interest. The photogeneration processes, however, are perhaps the best understood of any 

Ryan et al. (1979) described two-photon photoexcitation of anthracene. The thermalization distance was 40 A and independent of wavelength between 246 and 308 nm. It was argued that thermalization occurs by internal conversion until a long-lived state is reached. The process is similar to that proposed by Chance and Braun (1976) and Noolandi and Hong (1978, 1979). It was suggested that the same final state could be reached following one- or two-photon photoexcitation. 

Due to its relevance o single-layer photoreceptors, photogeneration in polymers is of considerable importance to xerography. The most widely studied are the polysilanes, poly(N-vinylcarbazole), and various doped polymers. 

The polyacenes form an important class of aromatic compounds, which can be derived from uncharged perimeters with AN+1 n electrons by introducing cross-links that produce only linearly annelated six-membered rings. Thus, the polyacenes are obtained by odd perturbations. 

The interactions between the different configurations of Equation (2.M) vary depending on the nature of the perturbation. The Cl problem is simplified considerably if some of the interactions of the Cl matrix Equation (2.12) vanish. If the perturbation is odd, the relative phase angle q vanishes, and only X and U can mix, whereas Y = (, - I 2)/(i / ) and V = ( 3 - 4)/(i ) already correspond to the Bb and Lb states. If 

The location of the absorption bands as well as their intensities can be discussed on the basis of the perimeter model and perturbation theory. In Example 2.6 it was shown that the transition dipole moments of the and 

The spectroscopic properties that derive from these arguments for perfectly symmetrical antiaromatic systems are of limited practical interest since [4A/]annulenes are subject to Jahn-Teller and pseudo-Jahn-Teller distortions and do not have C symmetry in reality. What makes these results useful is that they provide a starting point for the introduction of perturbations that convert the parent perimeters into n systems of real interest. 

The classification into N and P as well as the ordering and the polarization of the excited states is analogous to that of systems derived from uncharged 4N-electron perimeters. These results are important because quinones (26), for instance, can be viewed as derivatives of doubly positively charged 4N-electron perimeters. 

In order to discuss higher states, the orbitals nd or their 

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Pariser R 1956 Theory of the electronic spectra and structure of the polyacenes and of alternant hydrocarbons J. Chem. Rhys. 24 250-68... 

These batteries incorporate a polyacenic semiconductor (PAS) for the active material of the positive electrode, lithium for that of the negative electrode and an organic solvent for the electrolyte. PAS is essentially amorphous with a rather loose structure of molecular-size order with an interlayer distance of 4.0 A, which is larger than the 3.35 A of graphite [56, 57]. 

The batteries feature a high operating voltage of 2.0-3.3 V. The energy density of SL621 (diameter 6.8 mm, height 2.1 mm) is 6.5 Whl"1. It is applicable to various types of small, thin equipment requiring backup for memory and clock function. Table 15 shows the specifications of lithium—polyacene batteries [58],... 

Table 15. Specifications of secondary lithium-polyacene batteries...

Polyacene is classified as a material which does not belong to either soft or hard carbons [84], It is also made by heat-treatment of phenol resin. As the heat-treatment temperature is lower than about 1000 °C, polyacene contains hydrogen and oxygen atoms. It has a conjugated plane into which lithium ions are doped. It was reported that the discharge capacity of polyacene is more than 1000 mAhg. However, there are no practical lithium-ion batteries using polyacene. 

Naphthalenedicarboxylic acid is useful in the synthesis of linear polyacenes,8 3-halo-2-naphthoic acids,4 and 3-amino-2-naphthoic acid.4... 

Girreser U., Giuffrida D., Kohnke F. H., Mathias J. P., Philp D., Stoddart J. F. The Structure-Directed Synthesis of Cyclacene and Polyacene Derivatives Pure... 

These calculations have been conducted on the basis of RHF optimized geometries, considering the 6-31G basis set for the n-alkane compounds (11), and the 6-31G basis set for the polyacene series (12). In both cases, the basis set contention has been checked by comparison with more thorough investigations on small compounds, such as ADC[3] calculations (11a) on n-butane based on the 6-31IG, 6-31G and 6-31G basis, or the MRSDCI ionization spectrum of ethylene as obtained by Murray and Davidson (33) using a 196-CGTO basis set. 

Pyykko, P. and Zaleski-Ejgierd, P. (2008) From nanostrips to nanorings the elastic properties of gold-glued polyauronaphthyridines and polyacenes. Physical Chemistry Chemical Physics, 10, 114-120. 

The 327-670 GHz EPR spectra of canthaxanthin radical cation were resolved into two principal components of the g-tensor (Konovalova et al. 1999). Spectral simulations indicated this to be the result of g-anisotropy where gn=2.0032 and gi=2.0023. This type of g-tensor is consistent with the theory for polyacene rc-radical cations (Stone 1964), which states that the difference gxx gyy decreases with increasing chain length. When gxx-gyy approaches zero, the g-tensor becomes cylindrically symmetrical with gxx=gyy=g and gzz=gn. The cylindrical symmetry for the all-trans carotenoids is not surprising because these molecules are long straight chain polyenes. This also demonstrates that the symmetrical unresolved EPR line at 9 GHz is due to a carotenoid Jt-radical cation with electron density distributed throughout the whole chain of double bonds as predicted by RHF-INDO/SP molecular orbital calculations. The lack of temperature... 

Figure 12.1 Schematic series of aromatic polyacene molecules.

Because of this degeneracy and coexistence of these resonant structures one expects intrinsic conjugation defects to exist and be formed along the chain, the so-called Pople-Wamsley defects (34) which in the case of polyacenes and polydiacetylenes takes the form... 

Fig. 11 Correlation between electrochemical potentials and OMTS bands for more than ten compounds including polyacenes, phthalo-cyanines, and porphyrins. OMTS data were acquired both from tunnel junctions and STM measurements. The standard potential relative to the normal hydrogen electrode associated with the half reaction M(solution) + e-(vac) —> M-(solution) is the y axis. The three outliers are assigned to the ring oxidation of porphyrins. (Reprinted with permission from [26])...

Mazur U, Hipps KW (1994) Unoccupied orbital mediated tunneling resonance-like structures in the tunneling spectra of polyacenes. J Phys Chem 98 5824—5829... 

El-Sayed, M. A., Pavlopoulos, T. Polarization of the triplet-triplet spectrum of some polyacenes by the method of photoselection. J. Chem. Phys. 39, 834 (1963). 

Raghu, C., Anusooya Pati, Y., Ramasesha, S. Structural and electronic instabilities in polyacenes density-matrix renormalization group study of a long-range interacting model. Phys. Rev. B 2002, 65(15), 155204. 

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