We present a high-resolution photoelectron spectroscopy investigation of condensed films of benzene, naphthalene, anthracene, tetracene, and pentacene. High spectroscopic resolution and a systematic variation of the molecular size allow a detailed analysis of the fine structures. The line shapes of the C 1s main lines are analyzed with respect to the different contributions of inhomogeneous broadening, vibronic coupling, and chemical shifts. The shake-up satellite spectra reveal trends, which give insight into the charge redistribution within the molecule upon photoexcitation. In particular, the shake-up between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) increases in intensity and moves closer toward the C 1s main line if the size of the aromatic system is increased. An explanation is given on the basis of the delocalization of the aromatic system and its capability in screening the photogenerated core hole. A comparison of the HOMO-LUMO shake-up position to the optical band gap gives additional insight into the reorganization of the electronic system upon photoexcitation.

Very high-efficiency green organic light-emitting devices based on electrophosphorescence Applied Physics Letters 75, 4 (1999);

Melanins are promising materials for organic bioelectronics devices like transistors, sensors and batteries. In this study, the chemical structural changes of melanin synthesized, by the auto oxidation of L-DOPA, are analyzed for a new synthetic procedure that uses oxygen under pressure (4 to 8 atm). TEM, DLS, FTIR, NMR and XPS are use to characterize the material. Under oxygen pressure, melanin synthesis is accelerated, the polymer obtained is found to have structural differences most notably a higher number of carbonyl groups and different surface charges compared to conventional synthetic melanin. As a consequence it has higher homogeneity and it is soluble in water. To explain these findings a reaction mechanism is proposed based on current melanogenesis models.Keywords: Melanin, oxygen pressure, solubility, accelerated synthesis. E-mail address: joaovp281@gmail.comThis article is protected by copyright. All rights reserved.This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1002/pi.5185 Accepted Articleexample, thin films of synthetic melanin with good adherence and controllable thickness were made using layer-by-layer technique. It has also been reported that it is possible to obtain melanin films from electrochemical deposition methods, [8] An alternative to obtain good quality films is to modify the melanin structure preserving its main properties, but increasing its solubility or changing its aggregation state. The advantage of this approach is that all processing techniques used up to now for organic semiconducting polymers device production would be available for melanin. In addition, many routine advanced techniques dedicated to thin film or solution characterization could be used. In the last 15 years soluble melanin derivatives were synthesized using different functionalized groups. [14][15][16][17][18] In this study, we propose an alternative synthetic approach for a soluble melanin without any exotic functionalization using molecular oxygen under pressure. Molecular oxygen is considered an ideal oxidant in the context of "green chemistry"; it has low cost, is abundant and environmentally friendly, having thus academic and industrial interest. In addition the synthesis is found to be faster under oxygen pressure. EXPERIMENTALAll the commercially available chemicals were purchased from Acros or Sigma-Aldrich and were used without further purification. In what concerns reproducibility, more than 3 different syntheses were performed and similar optical and structural properties were obtained. Melanin synthesisThe synthesis of melanin was carried out using well-known procedures briefly described. [19] Initially 0.3 g of L-3,4-dihydroxyphenylalanine (L-DOPA) was dissolved in 60 mL of deionized water (Milli-Q), next 0.4 mL of ammonium hydroxide (NH 4 OH) is added, ...

Ultrafast electron dynamics in the low-femtosecond regime was evaluated for poly(thiophene) by resonant Auger spectroscopy using the corehole clock method. Sulfur KL 2,3 L 2,3 Auger decay spectra were measured as a function of the photon energy. Remarkable changes developed by tuning the photon energy along the sulfur 1s absorption edge, depending on the nature of the intermediate core excited states. Features characteristics of the Auger Resonant Raman effect were observed. Competition between core hole decay and delocalization of the photoexcited electron was monitored. Branching ratios of Raman (spectator) and normal Auger channels were calculated and electron delocalization times derived.

The bifunctionalization of graphene oxide (GO) has attracted attention as a promising tool for broadening applications, despite its many challenges, especially regarding site-specific reactions. Herein, we obtained mono-and bifunctionalized GO containing thiol and imidazole groups that were anchored on the carboxylic acid sites of GO via amidation reactions. We varied the bifunctionalization methodology and showed that consecutive addition of the reagents (containing imidazole and thiol groups) led to materials with higher degrees of functionalization, in contrast to their simultaneous addition. The functionalized materials were evaluated as nanocatalysts in the neutralization reaction of a toxic organophosphate. Also, it was evidenced that the effect of the mono-and bifunctionalized materials on the catalytic outcomes gives insight toward neighboring effects. All catalysts were effective in the reaction studied with the monofunctionalized materials (containing thiol or imidazole groups) showing similar activity. Among the bifunctionalized materials (with both thiol and imidazole moieties), the one with the lower degree of functionalization showed the best performance. This was attributed to a combination of mechanisms, strongly dependent on the neighboring groups: attraction on the GO surface, nucleophilic catalysis by thiol/imidazole groups, and bifunctional intramolecular catalysis, for example, by thiol and imidazole groups, assisting potential nucleophilic hydroxyl groups. Oddly, the bifunctionalized materials with the higher degree of functionalization did not show the most prominent activity; they were actually similar to the monofunctionalized ones. This can be attributed to the inhibition or hindering of some of the proposed mechanisms due to steric effects or a nonideal positioning of the groups. A lot remains to be clarified in this field, but one thing is clear: a higher degree of functionalization should not always be pursued because the application of the material is what should guide what characteristics should be determined. Several other applications should be impacted by neighboring effects, which are directly influenced by the functionalization procedure.