Reduced HOMO−LUMO Gap as an Index of Kinetic Stability for Polycyclic Aromatic Hydrocarbons

Abstract

A reduced HOMO−LUMO gap, which is defined as the HOMO−LUMO energy separation of a molecule divided by that of the hypothetical polyene reference, can be used as an index of kinetic stability for a variety of polycyclic aromatic hydrocarbons (PAHs). The reduced HOMO−LUMO gap < 1.00 indicates that the HOMO contributes to the decrease in the topological resonance energy. In general, PAHs with reduced HOMO−LUMO gaps < 1.30 are chemically very reactive. Fully benzenoid hydrocarbons are kinetically very stable with very large reduced HOMO−LUMO gaps. Many of the PAH molecules with large reduced HOMO−LUMO gaps are closed-shell substructures of nonmetallic one-dimensional benzenoid polymers.

Analysis of the Electronic Structure of Aqueous Urea and Its Derivatives: A Systematic Soft X‐Ray–TD‐DFT Approach

“…The knowledge about the electronic structure of urea in solution, however, is crucial for a deeper understanding of its behavior in chemical reactions. In particular, the energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) is of large interest since it serves as indicator for molecular properties like stability or reactivity (see, e.g., references [16][17][18][19] and references therein). The HOMO-LUMO gap itself, however, is strongly affected by an exchange of the functional groups of a molecule.…”

Effects of cluster formation on spectra of benzo[a]pyrene and benzo[e]pyrene

“…Although the HOMO-LUMO energy difference does not in general yield accurate spectral transition energies, it has in fact long been used to correlate with spectral shifts and other physicochemical properties of PAHs [25,26], and HOMO-LUMO differences do correlate satisfactorily with the shifts in λ max that accompany increases in the number of chromophores in PAHs, even to the extent of being able to distinguish among isomers [27].…”

Correlations of the Number of Dewar Resonance Structures and Matching Polynomials for the Linear and Zigzag Polyacene Series

“…19 In the plot of BRC versus HOMO, the zigzag phenacenes in Figure 7 appears to approach the Hosoya calculated limit HOMO value of 0.382 β as the number of rings increases; 8 (determined from the characteristic polynomial) divided by that of the hypothetical polyene reference which is devoid of cyclic contributions (determined from the matching polynomial) and is a measure of kinetic stability. 24 The contrasting difference in reactivity (kinetic stability) of the linear acenes versus the phenacenes is emphasized by the plots (Figures 8 and 9) of the number of Dewar resonance structures versus the reduced HOMO-LUMO gap index of Aihara. 24 If the reduced HOMO-LUMO gap index is < 1.3, then the PAH is chemically very reactive.…”

“…24 The contrasting difference in reactivity (kinetic stability) of the linear acenes versus the phenacenes is emphasized by the plots (Figures 8 and 9) of the number of Dewar resonance structures versus the reduced HOMO-LUMO gap index of Aihara. 24 If the reduced HOMO-LUMO gap index is < 1.3, then the PAH is chemically very reactive. Starting with benzene all total resonant sextet benzenoids have reduced HOMO-LUMO gap index > 1.93.…”