Pyrene Dimer Cation as Studied by Pulse Radiolysis

Radical cations of pyrene were investigated by the pulse radiolysis technique in solutions of benzonitrile, acetone, and dichloroethane. A 450‐nm absorption band of a pyrene monomer cation was replaced by new bands with maxima at 500, 580, and 750 nm as the pyrene concentration was increased. The latter absorption bands were exclusively assigned to a pyrene dimer cation in equilibrium with the monomer cation at room temperature. Equilibrium constants evaluated were ${\text{(2.7\hspace{0.17em}±\hspace{0.17em}0.2)\hspace{0.17em}×\hspace{0.17em}10}}^2\mathrm{and}{\text{(5.1\hspace{0.17em}±\hspace{0.17em}0.5)\hspace{0.17em}×\hspace{0.17em}10}}^2{M}^{\text{−1}}$ at 20°C for benzonitrile and acetone solutions, respectively. The decay processes of both the monomer and dimer cations were discussed. In addition, rate constants of the reactions of both the monomer and dimer cations with triethylamine were found to be ${\text{2.7\hspace{0.17em}×\hspace{0.17em}10}}^9\mathrm{and}{\text{5.4\hspace{0.17em}×\hspace{0.17em}10}}^8{M}^{\text{−1}}·{\sec }^{\text{−1}}$ , respectively.