Comparative study of diradical characters and third-order nonlinear optical properties of linear/cyclic acenes versus phenylenes

摘要

A long-range corrected spin-unrestricted density functional theory (LC-UDFT) approach has been used to investigate the diradical character (y _i) and third-order nonlinear optical properties of linear/cyclic [N]acenes and [N]phenylenes in their ground states, where N is the number of benzene rings in each linear and cyclic configuration. It has been found that linear and cyclic acenes with N = 5-10 show singlet diradical characters, while linear and cyclic phenylenes with equivalent number of benzene rings have closed-shell configurations. The amplitudes of third-order nonlinear optical polarizability (γ_(zzzz)) for open-shell linear/cyclic acenes are larger especially in intermediate range of diradical character than those of closed-shell phenylene counterparts. For example, the γ_(zzzz) values of [5]cyclic acene (y_0 = y_1 = 0.320) is 4.89 × 10~3 a.u. which is about 6 times larger than those of 0.80 × 10~3 a.u. for closed-shell [5]cyclophenylene. Similarly, γ_(zzzz) value of [5]linear acene is also about 9 times larger than its closed-shell [5]linear phenylene counterpart. Our results show interesting insights into the relationship among the architectures, diradical characters and γ_(zzzz) values of different acenes and phenylenes.