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).

No abstract

Tetrakis(4-methoxyphenyl)anthraquinodimethane 1(b) with a bent geometry undergoes reversible redox interconversion with twisted dication 1(t)2+ exhibiting a vivid change in color (electrochromism) accompanied by a drastic structural change. Electrochemical oxidation of bianthraquinodimethane 2(b) with a doubly bent structure to bianthrylidene-type twisted dication 2(t) 2+ proceeded smoothly, whereas the reverse conversion was less effective because 2(t) 2• generated upon reduction of 2(t) 2+ is a long-lived species to undergo side reactions.The o-and p-quinodimethanes (oQD and pQD) are representative cross-conjugated π-electron systems. Attachment of charge-stabilizing end groups on the exocyclic carbons provides a useful protocol to construct reversible redox systems, 13 where generation of the Clar's sextet facilitates their redox reactions (Scheme 1). As a successful example, we previously reported tetraaryl-substituted oQDs fused with two benzene rings (dibenzo-Ar 4 oQDs), which undergo facile 2e-oxidation to transform into the corresponding dications. 4 In the course of our continuing studies 5 on novel organic cationic dyes, we planned further exploitation of QD-based electrochromic systems, 6 including the study on the pQD-type isomer 1 of dibenzo-Ar 4 oQD (Scheme 2). Unlike the oQD counter part, π extension of the system could be attained easily in 1 by inserting an anthrylidene unit, as in bianthraquinodimethane 2. Here, we report the preparation and redox properties of 1 and 2, along with their electrochromic behavior based on the interconversion with the corresponding dications 1 2+ and 2 2+. We successfully isolated the dicationic salts, whose X-ray analyses demonstrated outstanding difference in geometry, namely the bent form in pQDs 1 and 2 and the twisted form in the dications 1 2+ and 2 2+. As in the case of dibenzo-Ar 4 oQD, the 4-methoxyphenyl group was chosen as an aryl group on the exocyclic carbons to attain sufficient stability in the dicationic state. By conducting the SuzukiMiyaura coupling 7 of 11,11,12,12-tetrabromo-9,10-anthraquinodimethane (3) 8 with 4-methoxyphenylboronic acid, 1 9 was obtained as colorless crystals in 99% yield. By using 11,11,11¤,11¤-tetrabromo-10,10¤-bianthraquinodimethane (4) 11 instead of 3, π-extended analogue 2 9 was obtained as pale yellow crystals in 81% yield (Scheme S1). 10Upon oxidation of 1 with 2 equiv of (4-BrC 6 H 4 ) 3 N•+ PF 6 ¹ in CH 2 Cl 2 , dicationic salt 1 2+ (PF 6 ¹ ) 2 9 was obtained as green lustrous crystals in 91% yields. The dication dye exhibits a strong absorption at 531 nm (log ¾ 5.20) in CH 2 Cl 2 , a characteristic of the diarylmethylium unit. A broad NIR absorption [710 (3.96)] was also observed, which is assignable to the intramolecular CT absorption from the anthracene moiety to the diarylmethylium units. Upon treatment of 1 2+ (PF 6 ¹ ) 2 with Zn dust in MeCN, 1 was regenerated in 96% yield. Because of steric repulsion between the bulky aryl groups and the peri-hydrogens on the anthracene unit, both 1 and 1 2+ would adopt se...

1,3-Bis[4-(dimethylamino)phenyl]isobenzofuran (1a) and a derivative were efficiently prepared through a sequence of reactions in a single batch reactor (time integration). The o-quinodimethane-type π-conjugation in 1a was confirmed by bond alternation determined by a low-temperature X-ray analysis. Brightly colored heterocycle 1a undergoes reversible two-stage one-electron oxidation, and electrolysis of 1a induces a vivid change in UV–vis–NIR absorptions exhibiting several isosbestic points (electrochromism).

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 2(2+), 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 b(2+) and 2 c(2+), 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 2(2+) 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.

Through gold(I)-catalyzed cascade cyclization as a key step, the title electron donor was prepared, which adopts a planar geometry, as confirmed by an X-ray analysis. Due to 1,4-phenylenediamine moiety incorporated in the framework, it undergoes reversible one-electron oxidation. Upon electrolysis, it exhibited an electrochromic response in the UV–vis–NIR region, which was accompanied by a drastic change in the fluorescence spectrum since only the neutral donor is highly fluorescent.

Upon electrochemical oxidation of configurationally stable (M)-4,5-dimethyl-9,10-dihydrophenanthrene attached with two spiroacridan units at the C9 and C10 positions [(M)-1c], a three-way-output response by UV–vis, FL, and CD spectra was realized via clean conversion to the corresponding bond-dissociated dication (Rax)-2c2+. Similar gradual changes were induced upon standing of an aerated MeCN solution of (M)-1c after the addition of CF3CO2H because the elongated C9–C10 bond was also cleaved by oxidative protonolysis to give (Rax)-2c2+.

Two-proton or two-electron transfer of the title biphenolic dication proceeds nearly simultaneously to induce 2,6'/2',6- or 6,6'-bond formation to give dioxapyrene or dihydrophenanthrene derivatives, respectively, with vivid changes in color (halochromism and electrochromism).