Peri-functionalized Pentacene

Reports of pentacene functionalized at the 6,13 positions using the aforementioned methods have appeared in the literature since the early 1940s [29]. These materials are more soluble than pentacene, and substitution at the central ring minimizes decomposition by dimerization. These materials are still sensitive to 

One of the most common uses for peri-substituted pentacene is as a red emitter in organic light-emitting diodes (OLEDs). Diphenylpentacene, for example, has a fluorescence quantum yield of 30% as a 0.55% dopant in Alq3, yielding OLED devices with efficiencies near the theoretical maximum [34]. Variation of the aryl substituents improves solubility and processing and can increase fluorescence quantum yield (for example, pentacene 25 has a composite fluorescence quantum yield of 32%) [35]. There is one report of the use of diaryl pentacenes in FET devices, but the performance was generally poor (hole mobility for vapor-deposited 23 was of the order of 10-8 cm2 V-1 s-1) [30]. 

The most dramatic difference between unfunctionalized pentacene and the silyl-ethynylated pentacenes is the change from edge-to-face interaction to face-to-face 

Several sets of calculations of the band structure of pentacene cover the polymorphs and thin-film forms reported for this compound [42]. They show modest dispersions (0.1-0.2 eV) with a two-dimensional electronic nature. Band-structure calculations for functionalized pentacenes 27 and 29 support the measured band gap findings [43], In the one-dimensional re-stacked compound 27, calculations show a small gap along one crystallographic axis, with a remarkable 0.86 eV dispersion in the conduction band. In the two-dimensional re-stacked material 29, the calculation showed small band gaps along two crystallographic axes, with dispersions of the order of 0.3 eV in the conduction band. In principle, the performance of these materials should be similar to that of unfunctionalized pentacene. 

An alternative measurement of the electronic properties of single crystals relies on an all-optical pump-probe technique, which measures the mobility of photogen- 

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