The incorporation of F atoms endows a diethenylbiphenyl-based electron donor with configurational stability and S_NAr reactivity. The former enables the dynamic redox pair of (R_ax)-1/(R_ax,R,R)-1²⁺ to exhibit drastic UV/Vis and CD spectral changes upon electrolysis, whereas the latter makes it possible for (R_ax)-1 to serve as a useful chiral synthon for the production of larger assemblies [(R_ax,R_ax)-2 d,p,m and (R_ax,R_ax,R_ax)-3] containing two or three dyrex units. These dyads and triad also exhibit a clean electrochiroptical response with isosbestic points owing to one-wave multi-electron transfer.

The incorporation of F atoms endows a diethenylbiphenyl-based electron donor with configurational stability and S_NAr reactivity. The former enables the dynamic redox pair of (R_ax)-1/(R_ax,R,R)-1²⁺ to exhibit drastic UV/Vis and CD spectral changes upon electrolysis, whereas the latter makes it possible for (R_ax)-1 to serve as a useful chiral synthon for the production of larger assemblies [(R_ax,R_ax)-2 d,p,m and (R_ax,R_ax,R_ax)-3] containing two or three dyrex units. These dyads and triad also exhibit a clean electrochiroptical response with isosbestic points owing to one-wave multi-electron transfer.

Upon reduction of a 1H-cyclobuta[de]naphthalene-4,5-diylbis(diarylmethylium) species, a new CC bond is formed between the C_α and C_ortho atoms of the two chromophores, which presents an unprecedented coupling pattern for the dimerization of two trityl units. By attaching an annulated cyclobutane ring at the opposite peri position of the naphthalene core, the distance between the C_α carbon atoms was elongated beyond the limit of σ-bond formation through “scissor effects”. The suppression of C_αC_α bond formation, which would lead to hexaphenylethane-type compounds, is key to the first successful isolation of the α,o-adducts. The 5-diarylmethylene-6-triarylmethyl-1,3-cyclohexadiene unit in the α,o-adducts is stable, and isomerization of the cyclohexadiene unit into an aromatic system was not observed. The newly formed C_αC_ortho bond was cleaved upon two-electron oxidation to regenerate the dicationic dye.

10-Methylacridinium is a stable aromatic cation exhibiting yellow-orange color and strong green fluorescence (FL), and can be used as a versatile building block in constructing a wide variety of novel π-electron systems. The dications with the two chromophores connected by a proper π spacer undergo reversible “dyrex” (dynamic redox) behavior, and C–C bond formation/cleavage is accompanied by their redox reactions. The prototype is biphenyl-2,2′-diylbis(10-methylacridinium), which exhibits electrochromic response with ON/OFF switching of FL during the reversible interconversion with the di(spiroacridan)-type electron donor. Slight structural alteration under the concept of “MFMS” (maximum function on the minimum skeleton) endowed the dyrex system with metal-binding or chiroptical properties, which could be modified by the redox reactions. Some of the di(spiroacridan) derivatives generated from bis(10-methylacridinium)s have extreme structural parameters, such as the greatest C–C bond length ever reported.

Upon reduction of a 1H-cyclobuta[de]naphthalene-4,5-diylbis(diarylmethylium) species, a new CC bond is formed between the C_α and C_ortho atoms of the two chromophores, which presents an unprecedented coupling pattern for the dimerization of two trityl units. By attaching an annulated cyclobutane ring at the opposite peri position of the naphthalene core, the distance between the C_α carbon atoms was elongated beyond the limit of σ-bond formation through “scissor effects”. The suppression of C_αC_α bond formation, which would lead to hexaphenylethane-type compounds, is key to the first successful isolation of the α,o-adducts. The 5-diarylmethylene-6-triarylmethyl-1,3-cyclohexadiene unit in the α,o-adducts is stable, and isomerization of the cyclohexadiene unit into an aromatic system was not observed. The newly formed C_αC_ortho bond was cleaved upon two-electron oxidation to regenerate the dicationic dye.

Electron-donating dihydrobenzindolocarbazoles (BICs) 1 a–c, which adopt planar disk-shaped geometries, were prepared by gold(I)-catalyzed cyclization as a key step. Due to the presence of a 1,4-phenylenediamine (PD) moiety in the framework, they undergo reversible one-electron oxidation to the corresponding Wurster’s Blue (WB)-type species that exhibits NIR absorptions up to λ=1200 nm. In the case of the N,N′-dimethyl derivative, cation radical 1 c^+. is stable enough to be isolated as a salt and X-ray analysis indicated paraquinoid-type bond alternation in the WB core unit, whereas the bond lengths in the peripheral benzene rings are identical to those in the neutral donor. Upon electrochemical interconversion, the redox pairs of 1 a–c and 1 a–c^+. exhibited an electrochromic response in the UV/Vis/NIR region, which was accompanied by a drastic change in the fluorescence spectrum because only neutral donors 1 a–c are highly emissive (Φ_F: 0.7–0.8).

When two benzene rings are fused to a tetraaryl-o-quinodimethane skeleton, sterically hindered helical molecules 1 acquire a high thermodynamic stability. Because the tetraarylbutadiene subunit contains electron-donating alkoxy groups, 1 undergo reversible two-electron oxidation to 2²⁺, which can be isolated as deeply colored stable salts. Intramolecular transfer of the point chirality (e.g., sec-butyl) on the aryl groups to helicity induces a diastereomeric preference in dications 2 b²⁺ and 2 c²⁺, which represents an efficient method for enhancing circular-dichroism signals. Thus, those redox pairs can serve as new electrochiroptical response systems. X-ray analysis of dication 2²⁺ revealed π–π stacking interaction of the diarylmethylium moieties, which is also present in solution. The stacking geometry is the key contributor to the chirosolvatochromic response.

Imine-bridged rotaxanes are a new type of rotaxane in which the axle and macrocyclic ring are connected by imine bonds. We have previously reported that in imine-bridged rotaxane 5, the shuttling motion of the macrocycle could be controlled by changing the temperature. In this study, we investigated how the axle and macrocycle structures affect the construction of the imine-bridged rotaxane as well as the dynamic equilibrium between imine-bridged rotaxane 5 and [2]rotaxane 7 by using various combinations of axles (1 A,B), macrocycles (2 a–e), and side-stations (XYL and TEG). In the threading process, the flexibility of the macrocycle and the substituent groups at the para position of the aniline moieties affect the preparation of the threaded imines. The size of the imine-bridging station and the macrocyclic tether affects the hydrolysis of the imine bonds under acidic conditions.

3,3,4,4-Tetaaryldihydro[5]helicenes (1) and 1,1′-binaphthyl-2,2′-diylbis(diarylcarbenium)s (2²⁺) can be reversibly interconverted upon electron transfer, which is accompanied by a vivid color change (electrochromism) as well as by the formation/cleavage of a CC bond (“dynamic redox behavior”). Because only the neutral donor 1 exhibits strong fluorescence, electrochemical input can further modify the fluorescent properties of the pair. Due to the configurational stability of the helicity in 1 and axial chirality in 2²⁺, the redox reaction of optically pure material proceeds stereospecifically, which induces a chiroptical change such as circular dichroism (CD) as an additional output. The CD spectra of dications 2²⁺ exhibit solvent dependency (chiro-solvatochromism), which is accompanied by solvatochromic behavior based on the π–π interaction of the two cationic chromophores as well as coordinative interaction of the Lewis basic solvent to the Lewis acidic triarylcarbenium moieties. Thus, the present system is endowed with multi-input functionality for modifying multiple output signals.