Electrochromism of Nanographenes in the Near-Infrared Region

Nanographene (NG) is a potential candidate for organic EC materials because of its large pi-conjugated system, chemical stability, absorption band covering the visible region, and tunable optical properties by postsynthetic modification. We show that NGs carrying redox-active triphenylamine (TPA) units covalently linked to the NG edge function as EC materials in the NIR region. The hybrid materials can be obtained by the installation of TPA units onto the NG edge and display changes in the absorption spectrum in the NIR region extending to a wavelength of over 2000 nm upon one-electron oxidation and reduction at low potentials (<1.1 V). Time-dependent unrestricted density functional theory calculation of a model NG at the UB3LYP/6-31G(d,p) level of theory suggests that a narrow energy gap between the basal plane and the oxidized TPA unit is responsible for the observed EC function in the NIR region.

Automated summary

Nanographene is a promising candidate for organic electrochromic (EC) materials due to its large pi-conjugated system, chemical stability, and tunable optical properties. In this study, nanographene carrying redox-active triphenylamine units covalently linked to the edge exhibited EC behavior in the near-infrared (NIR) region. The absorption spectrum of the hybrid material changed upon one-electron oxidation and reduction at low potentials, extending to a wavelength of over 2000 nm.