First-Principles Study on Redox Magnetism and Electrochromism of Cyclometalated Triarylamine-Core Triruthenium Complex

Lin Li,Meng-Yang Chen,Wei-Feng Sun,Jian-Quan Liang,He-Qian Liu,Yue Wang,Jian Zhang,Yu-Xuan Sun,Wei Song

doi:10.3390/cryst11010057

Abstract

Spin electronic states and optical properties of a circular ruthenium (Ru) terpyridine complex with a triarylamine core (CTTC) are theoretically investigated by first-principles calculations within an all-electron numerical orbital scheme based on spin density functional theory (SDFT), which demonstrate five well-defined redox states for electrochromic functions. Atomic structure of CTTC molecule is obtained by geometric optimization, and its electronic structure with a decreasing semiconductor band-gap exhibits five consecutive single-electron redox states of Ru-coordinated centers. Except for CTTC in (Ru)3+4 redox state exhibiting a net spin of 2.25 (ћ/2), the other redox states are almost zero in total spin. Density distribution and energy-splitting of spin states indicate that the ferromagnetic coupling of Ru cations coordinating with terpyridine/triarylamine ligands originates dominantly from the spin polarization of Ru 4d-orbitals coordinated by N- and C-2p electrons of triarylamine. CTTC molecule in each redox state represents a well-discriminated absorption in visible region, with the highest characteristic peaks locating at 24.2, 20.2, 21.3, and 19.3/21.7 (103 cm−1) and a manifold of peaks at 13.4~25.3 (103 cm−1) for +2~+6 redox states, respectively. Theoretical electronic structure and optics of CTTC complex are used to evaluate the underlying physical mechanism of realizing a multi-color visible electrochromism by four couples of redox pairs, which is suggested to be applied for monitoring electrical information.

Highlights

Electrochromism of electroactive molecules is a manifestation of the reversible switch between distinguishable redox states under electric excitation, displaying reversible alternations in optical properties and transparency, which plays an important role in energy conservation, building, and aerospace at present [1,2,3]
Triggered by these cyclometalated ruthenium complexes with four redox states at lowpotentials, in the present study, we investigate a cyclometalated triruthenium complex with a triarylamine core by first-principles calculations of electronic structure and optoelectronic transition in various redox states, which accounts for its magnetism and multistate-redox electrochromics
A molecular model of the cyclometalated triruthenium complex with a triarylamine core and terpyridine terminals (CTTC) is initially constructed using Monte Carlo (MC) molecular simulation method [22] according to the reported chemical configuration, as shown in Figure 1 [23], which is used as the input structure for geometry optimization of energy minimization

Summary

Introduction

Electrochromism of electroactive molecules is a manifestation of the reversible switch between distinguishable redox states under electric excitation, displaying reversible alternations in optical properties and transparency, which plays an important role in energy conservation, building, and aerospace at present [1,2,3]. Ruthenium-amine-conjugated (cyclometalated ruthenium) complexes with low potential Ru(III/II)-C bonds have recently been characterized to represent a sufficient absorption discrimination in visible and near-infrared (NIR) regions through redox processes of at least three oxidation states [15,16,17,18], which show potential to be efficiently applied for electrochromic switches and variable optical attenuators in fiber-optic communications [19,20,21] Triggered by these cyclometalated ruthenium complexes with four redox states at lowpotentials, in the present study, we investigate a cyclometalated triruthenium complex with a triarylamine core by first-principles calculations of electronic structure and optoelectronic transition in various redox states, which accounts for its magnetism and multistate-redox electrochromics

Theoretical Calculation Methodology

Conclusions