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

Brandt, Jochen R.; Pospı́šil, Lubomı́r; Bednářová, Lucie; Costa, Rosenildo Corrêa da; White, Andrew J. P.; Mori, Tadashi; Teplý, Filip; Fuchter, Matthew J.

doi:10.1039/c7cc04903j

Cited by 32 publications

(39 citation statements)

References 45 publications

(43 reference statements)

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“…In 2017, Teply and Fuchter took advantage of the dimerization process of N-methyl-1azonia [6]helicene [(M)-254] + to perform an intense chiroptical switch. 253 In its turn, the latter was bis-oxidized to [(M,M)-255] 2+ which spontaneously dissociated back to [(M)-254] + (Scheme 63a). Following the ECD responses at two different wavelengths, i.e.…”

Section: Other Azoniahelicenesmentioning

confidence: 99%

Enantioenriched Helicenes and Helicenoids Containing Main-Group Elements (B, Si, N, P)

2019

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In this review, we discuss the rich chemistry of helicenes and helicenoids containing maingroup elements. Enantioenriched helicenic derivatives containing main-group elements B, Si, N and P, either incorporated within the helical backbone or grafted to it, will be thoroughly presented. We will describe their synthesis, resolution, and asymmetric synthesis, their structural features, electronic and chiroptical properties, emission, together with other photochemical properties and applications. OUTLINE 14 The absorption spectrum of 19c recorded in CH 2 Cl 2 solutions exhibited a maximum at 376 nm which is significantly red shifted compared with that of double [5]helicene 19a (310 nm) due to the more extended π-conjugation in 19c. According to TD-DFT calculations, the low-energy absorption band from 400 to 500 nm is assignable to the HOMO→LUMO transition corresponding to a π−π* transition of the fully conjugated bis-helical system. DFT calculations revealed a very high theoretical isomerization barrier of 45.1 kcal/mol for the (P,P)/(M,M)-19c stereoisomer, i.e. 4.4 kcal/mol higher than the (P,M) stereoisomer (not observed experimentally). The high configurational stability of 19c enabled to obtain the pure (P,P)and (M,M)-19c by chiral HPLC (Daicel Chiralcel IE column; EtOAc/MeOH = 9:1 as eluent) and to study their chiroptical properties. The ECD spectrum of (P,P)-19c in CH 2 Cl 2 displayed two strong positive bands at 275 and 320 nm, a strong negative one at 375 nm and a broad and less intense one between 425-475 nm. 52 Note that the isomerization barrier of the OBO-fused double [7]helicene is much higher than for oxabora[6]helicene 9 (vide supra) and higher than carbo[7]helicene (42.0 kcal/ mol), indicating the advantage of double helicenes over monohelicenes in terms of conformational stability. Indeed no racemization was observed upon heating enantiomer (P,P) and (M,M)-19c for 24 h up to 200 °C. 52 Note that in 2017 a longer double OBO-helicene analogue was deposited on a Au(111) under UHV conditions and its surface-assisted cyclodehydrogenation into a planar OBO-perihexacene was observed by STM. 54 Similarly to 6 and 9, the strong bond alternation found in the BOC4 rings of 19a 51 may account for the small NICS value of 1.3 while the surrounding C6 rings, including the distorted central benzene ring, show large negative NICS values (Scheme 3c). For comparison, in the all-carbon analogue tetrabenzo-[a,f,j,o]perylene shown in Scheme 3c, the central C6 ring shows a positive NICS value, indicating substantial antiaromatic character. Notably, molecular orbital calculations of 19a indicate that the HOMO and LUMO are spread over the C6 rings rather than on the boron and oxygen atoms, accounting for the substantial stability of 19a (Scheme 3c). Borahelicenes are efficient blue fluorophores. Indeed, azabora[6]helicene 6 displays blue fluorescence at 447 nm (Table 2), while smaller achiral [4]helicenic systems were successfully used as host materials in phosphorescent OLEDs with efficiencies better than the classical 4,4'...

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Section: Other Azoniahelicenesmentioning

confidence: 99%

Enantioenriched Helicenes and Helicenoids Containing Main-Group Elements (B, Si, N, P)

2019

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“…A further level of complexity arises from the pseudo-C2 symmetry of the monoaza [6]helicenes. In a recent paper, 31 the authors observed a certain degree of occupational disorder in the crystal structure of the enantiopure 1-aza [6]helicene due to the position of the nitrogen. Therefore, we included in our calculations the cases with 'opposite' occupancy, where every helicene in the cell is rotated by 180° around its pseudo-C2 symmetry axis (see Figure 1).…”

Section: Methodsmentioning

confidence: 99%

The influence of nitrogen position on charge carrier mobility in enantiopure aza[6]helicene crystals

Salerno

Rice

Schmidt

et al. 2019

Phys. Chem. Chem. Phys.

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“…Switching of the ECD signal by potential pulses can be used as a read-out method of the state of a molecular ON/OFF switch storing the binary information in a system monomer/dimer. [30] This communication reports the redox switching of ECD of redox systems containing seven-membered rings (Scheme 1). We focused on tetra-cationic compounds 1 and 2, which show a reversible electron transfer facilitated by two redox active ethenylpyridinium arms in α or γ position with respect to nitrogen atoms.…”

Section: Introductionmentioning

confidence: 98%

“…The effect is not due to a change of chirality. Switching of the ECD signal by potential pulses can be used as a read‐out method of the state of a molecular ON/OFF switch storing the binary information in a system monomer/dimer …”

Section: Introductionmentioning

confidence: 99%

Chiroptical Redox Switching of Tetra‐Cationic Derivatives of Azoniahelicenes

Rončević¹,

Jirásek²,

Severa³

et al. 2019

ChemElectroChem

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New tetra‐ and di‐cationic azoniahelicenes provide electrochemical, spectroelectrochemical and electronic circular dichroism (ECD) data reflecting their differences in electron transfer (ET) kinetics. Di‐cationic helquats containing two seven‐membered rings are irreversibly reduced in two ET steps. Substitution by redox‐active ethenylpyridinium in the α or γ position with respect to nitrogen atoms of the helquat core yields tetra‐cationic derivatives with reversible ET steps and communicating redox centres. Redox‐inactive substituents in di‐cationic azoniahelicenes retain ET irreversibility. Redox switching of ECD of tetra‐cationic enantiomers was observed. Unlike fully aromatic helquat, the ECD response of tetra‐cationic helquats to periodic reduction‐oxidation cycles is slower, owing to a strong adsorption on electrodes. Quantum chemical calculations (DFT) indicate that the first ET step of tetra‐cationic derivative substituted in the γ position yields a folded structure, which favours the internal donor‐acceptor interaction. This explains the spectroelectrochemical differences between both tetra‐cations.

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

Abstract: Electrochemically-reversible dimerisation of an azoniahelicene provides a chiroptical switching system that exhibits significant hysteresis and thereby a large area of bistability.

Cited by 32 publications

References 45 publications

Enantioenriched Helicenes and Helicenoids Containing Main-Group Elements (B, Si, N, P)

Enantioenriched Helicenes and Helicenoids Containing Main-Group Elements (B, Si, N, P)

The influence of nitrogen position on charge carrier mobility in enantiopure aza[6]helicene crystals

Chiroptical Redox Switching of Tetra‐Cationic Derivatives of Azoniahelicenes

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