Naphthalenyl, anthracenyl, tetracenyl, and pentacenyl radicals and their anions

Electronic structure theory has been applied to the naphthalene-, anthracene-, tetracene-, and pentacene-based radicals and their anions. Five different density functional methods were used to predict adiabatic electron affinities for these radicals. A consistent trend was found, suggesting that the electron affinity at a site of hydrogen removal is primarily dependent upon steric effects for polycyclic aromatic hydrocarbons. The results for the 1-naphthalenyl and 2-naphthalenyl radicals were compared to experiment, and it was found that B3LYP appears to be the most reliable functional for this type of system. For the larger systems the predicted site specific adiabatic electron affinities of the radicals are 1.51 eV (1-anthracenyl), 1.46 eV (2-anthracenyl), and 1.68 eV (9-anthracenyl); 1.61 eV (1-tetracenyl), 1.56 eV (2-tetracenyl), and 1.82 eV (12-tetracenyl); and 1.93 eV (14-pentacenyl), 2.01 eV (13-pentacenyl), 1.68 eV (1-pentacenyl), and 1.63 eV (2-pentacenyl). These electron affinities are 0.5-1.5 eV higher than those for the analogous closed-shell singlet polycyclic aromatic hydrocarbons (PAHs); i.e., EA(anthracene) = 0.53 eV. The global minimum for each radical does not have the same hydrogen removed as the global minimum for the analogous anion. With this in mind, the global (or most preferred site) AEAs are 1.37 eV (naphthalenyl), 1.64 eV (anthracenyl), 1.81 eV (tetracenyl), and 1.97 eV (pentacenyl)