Iron Alkynyl Helicenes: Redox‐Triggered Chiroptical Tuning in the IR and Near‐IR Spectral Regions and Suitable for Telecommunications Applications

Abstract

The combination of a bis-alkynyl-helicene moiety with two iron centers leads to novel electroactive species displaying unprecedented redox-triggered chiroptical switching. Upon oxidation, strong changes of vibrational modes (either local or extended coupled modes) are detected by vibrational circular dichroism and Raman optical activity. Remarkably, the sign of the optical rotation at 1.54 µm (that is, at wavelengths typically used for telecommunications) changes upon oxidation while the topology and stereochemistry of the helicene remain unchanged.

Intense redox-driven chiroptical switching with a 580 mV hysteresis actuated through reversible dimerization of an azoniahelicene

“…[5][6][7] Of particular interest are helicene-based switches, 8 since the exceptionally intense chiroptical properties 9-11 of helicenes could lead to a large increase in the magnitude of the differential chiroptical signal and such molecules have already been successfully exploited in technological applications. [12][13][14][15][16][17] In most cases, the switching of these helicenes through changes in electrochemical potential (redox switching) has been achieved via reduction or oxidation of electronically biased helicenes [18][19][20][21] or helicene-coordinated transition metals, [22][23][24][25][26] leading to strong chiroptical switching D(De) of up to 135 M À1 cm À1 (see Fig. 1A left) 21 and even chiroptical switching at wavelengths suitable molecular systems are based on simple, reversible redox reactions with little or no significant structural change of the helicene, 27 the difference between the ''ON'' and the ''OFF'' potentials (redox hysteresis) is small and on the order of 60 mV (e.g.…”

Redox‐triggered chiroptical switching activity of ruthenium(III)‐bis‐(β‐diketonato) complexes bearing a bipyridine‐helicene ligand

“…21,22 Geometry optimizations were performed for tmhd/bipyridine-helicene complexes of Ru(III) ((P,Δ)- [4] .+ and (P,Λ)- [4] .+ in a spin-doublet d 5 electronic configuration, Figure 1) and of Ru(II) SCHEME 1 Preparation of the mixed-ligand Ru(III) complex [4] .+ ,PF 6 − . NH 4 PF 6 , CH 3 CN, reflux, 1 hour, 90%; (ii) bipyridine-carbo [6] helicene (rac-, P-or M-3), DMF, 140°C, 3 hours, 85% ((P,Δ)-4 and (P,Λ)-4 in a closed-shell d 6 configuration). H 2 SO 4 , aq.…”

“…3 In this context, several classes of organometallic helicene-based complexes have been investigated in our groups, including (1) ruthenium(II)-vinyl- 4,5 and iron(II)-ethynyl-carbo [6] helicenes 6 displaying redox-triggered switching of not only ECD and OR responses but also vibrational circular dichroism and, in the case of the Fe system, even resonance Raman optical activity spectra, (2) cycloplatinated bipyridine- [6]helicene-based systems demonstrating acid/base-triggered tuning of ECD and circularly polarized luminescence signals, 7 and (3) a bis-helicenic terpyridine derivative revealing an efficient absorption and emission switching activity through zinc(II) coordination/decoordination processes. Herein, we describe the synthesis of stable octahedral Ru(III) complexes ( [4] .+ ,PF 6 − , Scheme 1) bearing a helicenic bipyridine and two tmhd (tmhd: 2,2,6,6-tetramethyl-3,5heptanedionato) ligands. Herein, we describe the synthesis of stable octahedral Ru(III) complexes ( [4] .+ ,PF 6 − , Scheme 1) bearing a helicenic bipyridine and two tmhd (tmhd: 2,2,6,6-tetramethyl-3,5heptanedionato) ligands.…”

“…Indeed, bipyridines are widely used ligands that can stabilize metal centers through their strong σ-donating and weak π-back-bonding character, 9,10 while π-conjugated electron-rich β-diketonate ions, such as acac (acac: 2,4-pentanedionate) or tmhd, are known to support mixed-ligand Ru complexes, and, due to their non-innocent behavior, can consequently give access to stable compounds with electroactive properties. 2 and racemic and enantiopure bipyridine-carbo [6]helicene (rac-, P-, or M-3) were prepared according to literature procedures. Spectroelectrochemical studies have demonstrated that the complexes reveal an efficient redox-triggered chiroptical switching, thus yielding a new example of organometallic helicene-based switch.…”

“…Spectroelectrochemical studies have demonstrated that the complexes reveal an efficient redox-triggered chiroptical switching, thus yielding a new example of organometallic helicene-based switch. Then, the solvent was stripped off, and the crude compound was purified by silica gel chromatography (THF as the eluent), yielding rac- [4] .+ ,PF 6 − as a brown solid (25 mg, 85%). 7,15 2.2 | Synthesis of racemic [4] .+ ,PF 6 − To a solution of 2 (20 mg, 0.03 mmol) in DMF (3 mL) was added a solution of rac-3 (12 mg, 0.03 mmol) in DMF (3 mL).…”