Enhancement of NIR‐Absorbing Ability of Bis(diarylmethylium)‐Type Dicationic Dyes Based on an Ortho‐Substitution Strategy.

Abstract

Electrochromic systems capable of switching nearinfrared (NIR) absorption are fascinating from the viewpoint of applications in the materials and life sciences. Although 11,11,12, (AQDs) with a folded form undergo one-stage two-electron oxidation to produce twisted dicationic dyes exhibiting NIR absorption, there is a need to establish a design strategy that can enhance the NIR-absorbing abilities of the corresponding dicationic dyes. In this study, we designed and synthesized a series of AQD derivatives with various substituents introduced at the ortho-position(s) of the 4-methoxyphenyl group. X-ray and spectroscopic analyses revealed that NIR-absorbing properties can be changed by introduction of the orthosubstituents. Thus, control of the steric and electronic effects of the ortho-substituents on the 4-methoxyphenyl groups was demonstrated to be an effective strategy for fine-tuning of the HOMO and LUMO levels for neutral AQDs and twisted dications, respectively, resulting in the modification of electrochemical and spectroscopic properties under an "ortho-substitution strategy".

Domino‐Redox Reaction Induced by An Electrochemically Triggered Conformational Change

“…Such a change in structures between the neutral and cationic states is common with AQD derivatives A and C , [15,32] which is reflected in the redox behavior with large separation of the oxidation and reduction peaks (Figure S36). This would also be the case for SS‐BQD.…”

“…By an eight‐fold Suzuki–Miyaura cross‐coupling reaction, SS‐BQD 1 a with 4‐methoxyphenyl groups was prepared in 92 % yield in a one‐step manner from tetrakis(dibromomethylene) precursor 3 , which was prepared from tetraone 2 [36] (Figure 3a). In addition, to investigate the effect of a restricted change in the structure of the QD unit, [32] we prepared the reference compound 1 b with a chlorine atom at the 2‐position of the 4‐methoxyphenyl group in a similar manner (56 %).…”

“…[29] If they exhibit the domino process, the same idea could be applied for the much larger multi-redox systems to facilely generate oligo/poly-cations. In fact, B underwent one-wave four-electron (4e) oxidation to give tetracation B 4 + , however, this did not lead to the domino-redox reaction, because the oxidation potential of B is similar to that of monomeric AQD A with the same aryl groups, [15,[30][31][32] which undergoes one-wave 2e-oxidation. Thus, the oxidation behavior of multi-redox system B could instead be explained by the independent ET process of two QD units.…”