Heteroatom substitution in acenes allows tailoring of their remarkable electronic properties, expected to include spin-polarization and magnetism for larger members of the acene family. Here, we present a strategy for the on-surface synthesis of three undecacene analogs substituted with four nitrogen atoms on an Au(111) substrate, by employing specifically designed diethano-bridged precursors. A similarly designed precursor is used to synthesize the pristine undecacene molecule. By comparing experimental features of scanning probe microscopy with ab initio simulations, we demonstrate that the ground state of the synthesized tetraazaundecacene has considerable open-shell character on Au(111). Additionally, we demonstrate that the electronegative nitrogen atoms induce a considerable shift in energy level alignment compared to the pristine undecacene, and that the introduction of hydro-aza groups causes local anti-aromaticity in the synthesized compounds. Our work provides access to the precise fabrication of nitrogen-substituted acenes and their analogs, potential building-blocks of organic electronics and spintronics, and a rich playground to explore π-electron correlation.

Instances of a word drawn from different domains may have different sense priors (the proportions of the different senses of a word). This in turn affects the accuracy of word sense disambiguation (WSD) systems trained and applied on different domains. This paper presents a method to estimate the sense priors of words drawn from a new domain, and highlights the importance of using well calibrated probabilities when performing these estimations. By using well calibrated probabilities, we are able to estimate the sense priors effectively to achieve significant improvements in WSD accuracy.

A central problem of word sense disambiguation (WSD) is the lack of manually sense-tagged data required for supervised learning. In this paper, we evaluate an approach to automatically acquire sensetagged training data from English-Chinese parallel corpora, which are then used for disambiguating the nouns in the SENSEVAL-2 English lexical sample task. Our investigation reveals that this method of acquiring sense-tagged data is promising. On a subset of the most difficult SENSEVAL-2 nouns, the accuracy difference between the two approaches is only 14.0%, and the difference could narrow further to 6.5% if we disregard the advantage that manually sense-tagged data have in their sense coverage. Our analysis also highlights the importance of the issue of domain dependence in evaluating WSD programs.

The photo-induced generation of unstable molecules generally requires stringent conditions to prevent oxidation and the concomitant decomposition of the products. The visible-light-induced conversion of two heptacene precursors to heptacene wass tudied. Single crystals of bis-and mono-a-diketone-type heptacene precursors (7-DK2 and 7-DK1,r espectively), were prepared to investigate the effect of precursor structure on reactivity. The photoirradiation of a 7-DK2 single crystal cleaved only one a-diketone group, forminga ni ntermediate bearing ap entacenes ubunit, while that of a 7-DK1 single crystal gave rise to characteristic absorption peaks of heptacene and their increaseinintensity with photoirradiation time, indicating the generation of heptacene withoutd ecomposition. Heptacene productionw as not observed when the precursors were photoirradiated in solution, implying that the single crystal interiorp rovided isolation from the external environment, thus preventing heptacene oxidation.

The acene series, an important class of linearly polycyclic aromatic hydrocarbons, are of interest owing to their unique physicochemical features. With an increase in the number of fused benzene rings, acenes display an evolution of electronic structure and properties. Thus, efforts have been devoted to the synthesis of longer acenes, with dodecacene being the longest acene (12 fused benzene rings) reported to date. However, the formation of polymeric acenes with numerous benzene rings, namely polyacene, has yet to be realized. Herein, we present a methodology for the synthesis of polyacene mediated by a metal–organic framework. Nanoconfined synthesis of precursor polymers in the channels of the metal–organic framework and the subsequent dehydro-aromatization reaction produced polyacene that was overwhelmingly longer than the previously reported acenes. The scalable synthesis of polyacene allowed us to unveil the stability and electronic properties of polyacene, paving the way for their widespread applications in optoelectronic and magnetic devices.