Multistate Redox Switching and Near-Infrared Electrochromism Based on a Star-Shaped Triruthenium Complex with a Triarylamine Core

摘要

A star-shaped cyclometalated triruthenium complex >2(PF6)n (n = 3 and 4) with a triarylamine core was synthesized, which functions as a molecular switch with five well-separated redox states in both solution and film states. The single-crystal X-ray structure of >2(PF6)3 is presented. This complex displays four consecutive one-electron redox waves at +0.082, +0.31, +0.74, and +1.07 V vs Ag/AgCl. In each redox state, it shows significantly different NIR absorptions with λmax of 1590 nm for >2⁴⁺, 1400 nm for >2⁵⁺, 1060 nm for >2⁶⁺, and 740 nm for >2⁷⁺, respectively. Complex >2⁴⁺ shows a single-line EPR signal at g = 2.060, while other redox states are all EPR inactive. The spin density distributions and NIR absorptions in different redox states were rationalized by DFT and TDDFT calculations. A vinyl-substituted triruthenium analogous >3(PF6)4 was prepared, which was successfully polymerized on ITO glass electrode surfaces by reductive electropolymerization. The obtained poly->3ⁿ⁺/ITO film was characterized by FTIR, AFM, and SEM analysis. It shows four well-defined redox couples and reversible multistate NIR electrochromism. In particular, a contrast ratio (ΔT%) up to 63% was achieved at the optic telecommunication wavelength (1550 nm).