Polyarene anions: interplay between theory and experiment

Abstract

Polyarenes, or polycyclic aromatic hydrocarbons (PAHs), represent a ubiquitous and heavily studied type of compounds, appealing for their interesting spectroscopic, supramolecular, organometallic, and other properties. A major branch of research is concerned with polyarene anions: their electronic and structural properties, reactivity, aromaticity, and spectroscopy. This review describes the major role of computational investigations in complementing, explaining, and guiding experimental research, and thus providing invaluable contribution to our understanding of polyarene anions. The scope of this review focuses on polyarenes composed only from sp 2 -hybridized carbons and limits the discussion to the quantum-mechanical method of calculation. The topics covered include computation-assisted characterization; choice of methods; transformations induced by reduction, including anistropic charge redistributions, reorganization of bonding structure, flattening of curved polyarenes (buckybowls), and Jahn-Teller distortion; aromaticity topics such as ring currents and aromaticity measures; reactivity, for example, toward electrophilic substitution or ring closure, acidity and basicity, and self-assembly interactions in solution and in the gas phase; and finally, spectroscopy, mainly for astrochemical research, ranging from the mid-infrared to the far-ultraviolet spectral ranges. C 2011 John Wiley & Sons, Ltd.

Anionic derivatives of altan‐corannulene

“…On the other hand, their anions and cations generally have a distinctly different aromaticity character. [1][2][3] Therefore, the prohibitive role of antiaromaticity can become suggestive of possible syntheses of aromatic-charged species.…”

Electron affinity calculation for selected PAHs using DFT: Effect of cyclopenta ring fusion and aromaticity

“…4. The electron spin density distribution shows that the addition of an extra electron moves the excess electron density to the periphery of the molecule which is very much expected [3]. The sites of higher electron localization in the anions are indicated by the higher ESP value (by red color in Fig.…”

“…The delocalization of electrons and spread of the wave function over several atoms in the molecule facilitates multiple ionization of the molecule as well as accommodation of extra electrons [3]. It has been seen that molecules like C 60 can be experimentally detected with charge states as high as +12 and as low as À2 in vacuum [5,6] (À6 in solution phase [7]).…”

“…These molecules are one of the most abundant molecules in inter stellar space and are stable in the harsh radiation environment around stars [2]. The inherent structural attributes due to the carbon atoms make formation of large size PAHs possible and the strong delocalization of p-electrons leads to their inherent stability [3].…”

Benzene and Beyond: Pursuing the Core of Aromaticity

“…74 A half-century later a similar mixture of certainty and doubt was expressed in a major review: 'Aromaticity is probably the most prominent concept in chemistry whose very definition is still debated, being intuitively understood by all and rigorously defined by none'. 75 A 1970 Jerusalem conference exhibited a wide variety of opinions concerning the status and utility of the concept. 76 A minority held that it had long outlived its usefulness: I think we should all realize that we are united here in a symposium on a nonexistent subject […] aromaticity is not an observable property, i.e., it's not a quantity that can be measured and it's not even a concept which, in my experience, has proved very useful.…”