Hysteretic Tricolor Electrochromic Systems Based on the Dynamic Redox Properties of Unsymmetrically Substituted Dihydrophenanthrenes and Biphenyl-2,2'-Diyl Dications: Efficient Precursor Synthesis by a Flow Microreactor Method.

A series of biphenyl-2,2'-diylbis(diarylmethanol)s 3, which have two kinds of aryl groups at the bay region, were efficiently obtained by integrated flow microreactor synthesis. The diols 3NO/NX are the precursors of unsymmetric biphenylic dications 2NO/NX2+, which are transformed into the corresponding dihydrophenanthrenes 1NO/NX via 2NO/NX+• upon reduction, when they exhibit two-stage color changes. On the other hand, the steady-state concentration of the intermediate 2NO/NX+• is negligible during the oxidation of 1NO/NX to 2NO/NX2+, which reflects unique tricolor electrochromicity with a hysteretic pattern of color change [color 1→color 2→color 3→color 1].

1. Introduction

Electrochromism [1] is a representative function of organic redox systems, by which electrochemical input is reversibly transduced into UV-Vis spectral output. A vivid color change is a desirable feature of these systems, and thus the stable cationic dye moieties such as triarylmethyliums [2] have often been adon class="Chemical">pted for this purpose. During the course of our studies on “dynamic redox systems” [3,4] that undergo reversible C–C bond-formation/-breaking upon electron transfer, we found that 9,9,10,10-tetraaryl-9,10-dihydrophenanthrenes (DHP) 1 and biphenyl-2,2'-diylbis(diarylmethylium)s 22+ constitute a novel series of electrochromic pairs.

For example, the electron-donating DHPs (n class="Chemical">1NN, 1OO, 1XX) show absorptions only in the UV region, whereas the corresponding dications exhibit characteristic vivid colors (blue, red, or yellow) depending on the aryl group [λmax/nm (log ε) in MeCN: 661 (4.92), 604 (5.05) for 2NN2+; 539sh (4.72), 514 (4.87) for 2OO2+; 495sh (3.62) 460 (3.79) for 2XX2+] [5,6]. Mechanistic studies have indicated that interconversion proceeds via the biphenyl-2,2'-diyl-type cation radical 2+• as a common intermediate (Scheme 1) [6,7]. For the C2-symmetric derivatives shown above, however, this cation radical intermediate cannot be detected during the oxidation process of 1, since 2+• is more easily oxidized than 1 [Eox(1) > Eox(2+•)]. The same intermediate 2+• is also short-lived during the reduction of 22+, since 2+• undergoes facile disproportionation [E1red(22+)~E2red(22+)] into 22+ and 2••, the latter of which is instantaneously converted to 1 by intramolecular C–C bond-formation. In this way, two-color switching [color 1 (1) <=> color 2 (22+)] is induced upon the application of electrochemical input to redox pairs with C2-symmetry.

Scheme 1

Mechanism of interconversion between 1 and 22+.

We envisaged that the proper molecular design could incorporate the intermediate 2+• in a novel tricolor electrochromism: disproportionation of 2+• to 22+ and 2•• could be suppressed by attaching two kinds of n class="Chemical">aryl groups with different electron-donating properties. In this report we describe the preparation and novel electrochromic behavior of unsymmetrically substituted pairs such as 1NO/2NO2+ or 1NX/2NX2+. Flow microreactor synthesis [8,9,10,11,12,13,14,15,16,17,18,19] was very effective for sequentially attaching two different diarylmethyl units to the biphenyl skeleton, whereas the conventional macro batch method gave the desired products in low yields (ca. 10%). The color changes show hysteresis, in that there is a difference between oxidation [color 1 (1)→color 2 (22+)] and reduction [color 2 (22+)→color 3 (2+•)→color 1 (1)].

2. Results and Discussion

2.1. Preparation of Unsymmetrically Substituted Diol-Precursors

Biphenyl-2,2'-diylbis(diarylmethanol)s 3 n class="Chemical">are the precursors of dicationic dyes 22+ [5]. Diols with C2-symmetry were readily obtained by reacting diarylketone 4 and 2,2'-dilithiobiphenyl, the latter of which was generated in situ from 2,2'-dihalobiphenyl and 2 equiv. of BuLi at −78 °C (Scheme 2) [20]. To prepare unsymmetric diols 3NO or 3NX with two different diarylmethane units, we first used a mixture of two diarylketones (4N-4O, 4N-4X) as an electrophile. Though the desired unsymmetric diols were obtained as a mixture containing two symmetric diols and other byproducts, tedious chromatographic separation only afforded pure 3NO or 3NX in respective yield of 12% and 9% [6]. Attempts to improve the yield were unfruitful even when dihalobiphenyl was treated sequentially with BuLi (1 equiv.), diarylketone (1 equiv.), BuLi (another 1 equiv.), and another diarylketone (1 equiv.). Again, a mixture of three diols was obtained, since selective monolithiation is difficult under the conventional macro batch conditions even if 1 equiv. of BuLi is used [21].

Scheme 2

Preparation of precursor diols 3 under the macro batch conditions.

Preparation of precursor n class="Chemical">diols 3 under the macro batch conditions.

On the other hand, some of us recently demonstrated that monolithiation of dibromobiphenyl can be successfully conducted under the flow microreactor conditions [22,23]. By taking advantage of this process, we succeeded in the sequential introduction of two din class="Chemical">arylmethyl units by reaction integration using flow microreactor synthesis [24,25,26] (Figure 1) thanks to fast micromixing and precise temperature control. The best result was obtained when 0.1 M 2,2'-dibromobiphenyl in THF (flow rate 6.0 mL/min) was reacted with 0.5 M BuLi in hexane (1.2 mL/min) for 0.06 s at 24 °C to generate 2-lithio-2'-bromobiphenyl, which was sequentially reacted with ketone 4O (0.2 M in THF, 3.0 mL/min), BuLi (0.5 M in hexane, 1.44 mL/min), and another ketone 4N (0.1 M in THF, 7.2 mL/min). This sequence of reactions proceeded in a short period of 15.5 s, and, unsymmetric diol 3NO with 4-dimethylaminophenyl and 4-methoxyphenyl groups was generated in high NMR yield of 92% and isolated in 73% yield after chromatography. Under similar conditions, 3NX with 4-dimethylaminophenyl and xanthenyl groups was prepared in 81% NMR yield and isolated in 61% yield.

Figure 1

An integrated flow microreactor system for the sequential introduction of two different diarylmethanol units at the 2,2'-position of biphenyl.

Formula of compounds

In both 3NO and n class="Chemical">3NX, the two diarylmethyl units differ significantly in terms of their electron-donating properties, so that the combination would be suitable for suppressing the disproportionation of the cation radical intermediate (2NO+• and 2NX+•) during the electrochemical interconversion of 1 and 22+. In addition to its value in preparing the precursors of tricolor electrochromic systems shown above, the flow microreactor method can also produce another group of materials by adopting other bulky diarylketones with long alkoxy chains as an electrophile [e.g., 3,3',4,4'-tetrakis(octyloxy)- or tetrakis(hexadecyloxy)benzophenones, 4O or 4O]. Unsymmetrically substituted diols 3OO and 3OO were obtained in good isolated yields of 68% and 62%, respectively, and could be used to generate unique dicationic dyes that are soluble in a hydrocarbon solvent [7]. The results shown above clearly demonstrate that the flow microreactor system is very effective for the sequential introduction of two bulky substituents at the bay region of the biphenyl skeleton.

2.2. Preparation and Two-Electron Interconversion of Unsymmetrically Substituted Redox Pairs

When diols n class="Chemical">3NO and 3NX were treated with HBF4-(EtCO)2O, deeply colored dications were isolated as stable BF4 salts in respective yields of 91 and 93%. In the UV-Vis spectrum of 2NO2+(BF4−)2 [λmax/nm (logε) in MeCN: 632 (4.93), 519 (4.72)], both of the strong absorptions that are characteristic of two different triarylmethyliums are present. Thus, the deep purple color of 2NO2+(BF4−)2 solution is due to the simple combination of blue and red chromophores found in 2NN2+ and 2OO2+. Similarly, the green color of 2NX2+(BF4−)2 [632 (4.92), 488 sh (3.76), 425 (4.22)] can be accounted for by the presence of the blue and yellow dye units within the molecule.

These dications were cleanly converted into colorless DHPs, 1NO and 1NX, upon reduction with n class="Chemical">SmI2 in THF in respective yields of 97 and 78%. The resulting DHPs were reoxidized to 2NO2+ and 2NX2+ by treatment with 2 equiv. of (4-BrC6H4)3N+• SbCl6− in CH2Cl2, which were in turn isolated as deeply colored SbCl6− salts in respective yields of 82 and 79%. This high-yield interconversion indicates that 1NO/2NO2+ and 1NX/2NX2+ constitute a “reversible” redox pair although C–C bond-formation/-breaking is accompanied by electron transfer (“dynamic” redox behavior) [3,4].

According to an X-ray analysis of 1NX (Figure 2), the C9–n class="Gene">C10 bond of the DHP unit [1.643(6) Å] is longer than standard (1.54 Å) [27], which is due to the “front strain” [28] among the aryl groups at C9 and C10, as in the case of other polyarylated cyclic compounds [29,30,31,32]. The DHP skeleton adopts a half-chair conformation with a dihedral angle of 16.2° for two benzene nuclei, which endows the molecule with an asymmetric element of helicity (P/M). In a single crystal of 1NX (space group: P212121), all of the molecules adopt the same helicity, which shows that spontaneous resolution occurs. Based on the result of a VT-NMR experiment, however, the spectrum indicates C1-symmetry only at low temperature (N-methyl protons: 2.95 and 2.80 ppm in CDCl3), and Cs symmetry is attained at room temperature (Tc = −40 °C). P/M-1NX readily undergoes racemization due to facile ring-flip in solution (ΔG‡ = 11.4 kcal mol−1 at −40 °C) (Scheme 4), while this process is prohibited in the crystal.

Figure 2

Molecular structure of 1NX determined by X-ray analysis: (left) top view; (right) side view. The DHP skeleton adopts a helical geometry, and all of the molecules in a single crystal are homochiral in terms of helicity.

Scheme 4

Interconversion of the enantiomers of helical DHPs 1 by ring flip.

Molecular structure of n class="Chemical">1NX determined by X-ray analysis: (left) top view; (right) side view. The DHP skeleton adopts a helical geometry, and all of the molecules in a single crystal are homochiral in terms of helicity.

2.3. Hysteretic Redox Behavior of Unsymmetrically Substituted Redox Pairs

The cyclic voltammograms of C2-symmetric DHPs n class="Chemical">are similar to each other, with an irreversible 2e-oxidation peak at +0.77 (1NN), +1.47 (1OO) or +1.42 (1XX) V vs. SCE in CH2Cl2, respectively [5,6]. The return wave is largely shifted to the cathode, and was assigned to the 2e-reduction peak of 2NN2+ (−0.45 V), 2OO2+ (+0.18 V), or 2XX2+ (+0.50 V), respectively (Table 1). Similarly, the present unsymmetric DHPs 1NO and 1NX undergo irreversible 2e-oxidation (Figure 3). Their oxidation potentials are close to that of 1NN, indicating that the HOMO level of 1NO or 1NX is close to that of 1NN due to the dimethylaminophenyl groups with strong electron-donating properties. The irreversibility of the oxidation wave suggests that the as-generated cation radical, 1NO+• or 1NX+•, readily isomerizes to 2NO+• or 2NX+• by C9–C10 bond fission. In the return cycle of the voltammogram of 1NO or 1NX, two cathodic peaks were seen: such behavior is quite different from that of C2-symmetric compounds.

Table 1

Redox potentials of 1 and 22+ in CH2Cl2a.

compd.	Eox (1)	E1red (22+)	E2red (2+•)
NO	+0.83b,c	+0.10c	−0.45c
NX	+0.76b,c	+0.24c	−0.19c
NN	+0.74b,c	−0.42b,c
OO	+1.44b,c	+0.21b,c
XX	+1.39b,c	+0.53b,c

a E/V vs. SCE, 0.1 M Bu4NBF4, Pt electrode, scan rate 100 mV/s; b Two-electron process; c Irreversible wave, values are calculated. as Eox = Epeak − 0.03 and Ered = Epeak + 0.03.

Figure 3

Cyclic voltammogram of DHP 1NO (10−3 M) in CH2Cl2 (E/V vs. SCE 0.1 M Bu4NBF4, Pt electrode, scan rate 500 mV s−1). The reduction peaks are absent when the voltammogram is first scanned cathodically. As shown by the dotted line, the first reduction wave at +0.07 V is reversible when the scanning is reversed at −0.10 V.

a E/V vs. SCE, 0.1 M Bu4NBF4, n class="Chemical">Pt electrode, scan rate 100 mV/s; b Two-electron process; c Irreversible wave, values are calculated. as Eox = Epeak − 0.03 and Ered = Epeak + 0.03.

Cyclic voltammogram of DHP n class="Chemical">1NO (10−3 M) in CH2Cl2 (E/V vs. SCE 0.1 M Bu4NBF4, Pt electrode, scan rate 500 mV s−1). The reduction peaks are absent when the voltammogram is first scanned cathodically. As shown by the dotted line, the first reduction wave at +0.07 V is reversible when the scanning is reversed at −0.10 V.

Independent measurements of 2NO2+ and 2n class="Chemical">NX2+ confirmed that the two cathodic peaks are due to two-stage 1e-reduction processes of the unsymmetric dications. The first process is completely reversible, and corresponds to the reduction of bis(4-methoxyphenyl)methylium in 2NO2+ or the xanthenylium moiety in 2NX2+. Furthermore, after scanning of the irreversible second 1e-reduction wave of 2NO2+ and 2NX2+, the anodic peak due to the oxidation of 1NO or 1NX appears in the far anodic region of the voltammograms. Such redox properties can only be accounted for by assuming the reaction mechanism shown in Scheme 1, where the elongated C9–C10 bond in DHP is cleaved after just 1e oxidation of 1NO to 1NO+•[33] whereas two-fold 1e-reduction of 2NO2+ to 2NO•• is necessary before the ring closure. 2NO+• produced from 1NO+• is more easily oxidized than 1NO [Eox(1NO) = +0.83 V; Eox(2NO+•) = E1red(2NO2+) = +0.10 V], and thus the steady-state concentration of 2NO+• is negligible during the electrochemical oxidation of 1NO, although the same specimen is a long-lived intermediate in the reduction of 2NO2+ due to suppression of disproportionation. The same is true for another series of compounds, 1NX+•/1NX+•/2NX+•/2NX2+ [Eox(1NX) = +0.76 V; Eox(2NX+•) = E1red(2NX2+) = +0.24 V; E2red(2NX2+) = −0.19 V]. Thanks to the hysteretic interconversion in redox reactions, unique tricolor electrochromic systems could be constructed using the present unsymmetric derivatives, as shown below.

2.4. Hysteretic Tricolor Electrochromicity of Unsymmetrically Substituted Redox Pairs

Upon the electrochemical oxidation of colorless 1NO in n class="Chemical">CH2Cl2, both the blue and red chromophores grow simultaneously to develop a violet color for 2NO2+ (Figure 4(a), isosbestic point at 310 nm). On the other hand, the red chromophore predominantly disappears in the first stage of the electrochemical reduction of 2NO2+ (Figure 4(b), 295 nm), and the blue cation radical 2NO+• is then converted to colorless 1NO (Figure 4(c), 290 nm) even under constant-current electrolytic conditions (Scheme 5). A similar behavior, but with different colors, was observed for the xanthene derivative. Thus, colorless donor 1NX was transformed directly into green 2NX2+ (isosbestic point: 309 nm), whereas reduction is a two-stage process; i.e., green 2NX2+ changes to blue 2NX+• (248, 270, 300 nm) and blue 2NX+• changes to colorless 1NX (296 nm), which shows the generality of the unique pattern of the color change.

Figure 4

Changes in the UV–VIS spectra of (a) 1NO (3.5 mL; 3.0 × 10−5 M in CH2Cl2 containing 0.05 M Bu4NBF4) upon electrochemical oxidation (10 μA) at 5-min intervals, and 2NO2+ (3.5 mL soln; 6.2 × 10−6 M in CH2Cl2 containing 0.05 M Bu4NBF4) upon electrochemical reduction (40 μA): (b) stage 1, at 2-min intervals; (c) stage 2, at 8-min intervals.

Scheme 5

Hysteretic color changes in the novel tricolor chromic systems.

Changes in the UV–VIS spectra of (a) 1NO (3.5 mL; 3.0 × 10−5 M in n class="Chemical">CH2Cl2 containing 0.05 M Bu4NBF4) upon electrochemical oxidation (10 μA) at 5-min intervals, and 2NO2+ (3.5 mL soln; 6.2 × 10−6 M in CH2Cl2 containing 0.05 M Bu4NBF4) upon electrochemical reduction (40 μA): (b) stage 1, at 2-min intervals; (c) stage 2, at 8-min intervals.

3. Conclusions

Compared with the successful examples based on the n class="Chemical">polymeric materials [34,35,36,37,38,39,40,41,42,43,44,45,46], tricolor electrochromicity based on discrete molecules is rare, for which only a limited number of examples have been reported [47,48,49,50,51]. Even among successful examples, a hysteretic pattern for the color change, where there is a difference between oxidation [color 1→color 2] and reduction [color 2→color 3→color 1], is quite unique for the present systems. This novel chromicity is attained by the incorporation of biphenyldiyl-type cation radical 2+• as an additional component to DHP 1 and dication 22+. The key to extending the lifetime of 2+• is the different electron-donating properties of two dye chromophores, whose precursors were prepared very efficiently using the flow microreactor method.

We are now developing a new series of tricolor chromic system, which also afford chiron class="Chemical">ptical properties (e.g., circular dichroism (CD)) as an additional signal, to construct the multi-output response systems (Scheme 6) [3,4,7,52,53,54]. While the triarylmethyliums attached with chiral substituents only exhibit very small ellipticity to be used as an output signal (|Δε| < 1.5), huge enhancement (|Δε| > 100) could be realized by intramolecular transfer of the point chirality to the axial chirality in the biphenyl-diyl dications 22+ (Scheme 7) [54], in which the two triarylmethylium units are suitably arranged for effective exciton coupling [52,53]. Studies along this vein are now in progress and the results will be reported in due course.

Scheme 6

Multi-output response based on the novel tricolor chromic systems.

Scheme 7

Interconversion of the enantiomers of axially chiral dications 22+ by rotation to give a diasteromerically biased mixture due to the transfer of point chirality to axial chirality.

4. Experimental Section

4.1. Preparation of 9,9-Bis(4-Dimethylaminophenyl)-10,10-Bis(4-Methoxyphenyl)-9,10-Dihydrophenanthrene 1NO

To a suspension of dication salt of n class="Chemical">2NO2+(BF4−)2 (104 mg, 0.129 mmol) in THF (10 mL) was added triethylamine (3 mL) followed by SmI2 (0.1 mol dm−3 in THF, 5.0 mL, 0.50 mmol) over 10 min at rt. The violet suspension gradually turned to ocher, and then the blue color of SmI2 remained persistent during the addition. After stirring for 1 h and removal of THF and amine, the residue was suspended in water and extracted with benzene. The organic layer was washed with water and brine, and dried over K2CO3. Evaporation of solvent followed by chromatographic separation (Al2O3, benzene) gave DHP 1NO as a colorless solid (79 mg, y. 97%).

Mp 284.5–285.5 °C (decomp.); 1H NMR (400 MHz, n class="Chemical">CDCl3, 0 °C) δ/ppm 7.65–7.71 (2H, m), 7.18–7.25 (2H, m), 7.08–7.18 (4H, m), 6.80–7.06 (8H, m), 6.43–6.55 (4H, AA’XX’), 6.26–6.38 (4H, AA’XX’), 3.71 (6H, s), 2.85 (12H, s); IR (KBr) 2948, 2832, 1610, 1510, 1444, 1354, 1292, 1252, 1186, 1036, 950, 806, 746, 580 cm−1; FD-MS m/z 630 (M+, BP); Anal. Calcd. for C44H42N2O2: C, 83.78; H, 6.71; N, 4.44. Found: C, 83.72; H, 6.88; N, 4.48.

4.2. Preparation of Spiro[10,10-Bis(4-Dimethylaminophenyl)-9,10-Dihydrophenanthrene-9,9'-[9H]Xanthene] 1NX

To a suspension of 2NX2+(BF4−)2 (30 mg, 39.6 μmol) in n class="Chemical">THF (10 mL) was added SmI2 (0.1 mol dm−3 in THF, 1.7 mL, 0.17 mmol) over 5 min at rt. The deep green suspension gradually turned to colorless during the addition. After stirring for 30 min and evaporation of THF, the residue was suspended in water and extracted with CH2Cl2. The organic layer was washed with water and brine, and dried over Na2SO4. Evaporation of solvent followed by separation by preparative TLC (SiO2, hexane/AcOEt = 4) gave DHP 1NX as a colorless solid (18 mg, y. 78%). Single crystalline specimen of 1NX was obtained by recrystallization from ether.

Mp 294–295 °C (decomp); 1H NMR (400 MHz, n class="Chemical">CDCl3, 24 °C) δ/ppm 8.03 (1H, d, J = 7.8 Hz), 7.90 (1H, d, J = 7.8 Hz), 7.46 (1H, ddd, J = 7.8, 7.8, 1.5 Hz), 7.34 (1H, dd, J = 7.8, 1.5 Hz), 7.22–7.30 (3H, m), 7.13–7.19 (2H, m), 6.88–7.05 (3H, m), 6.63–6.72 (6H, m), 6.61 (2H, dd, J = 7.8, 1.5 Hz), 6.24 (4H, AA’XX’), 2.84 (12H, s); IR (KBr) 2796, 1610, 1518, 1480, 1440, 1354, 1312, 1244, 950, 808, 750 cm−1; FD-MS m/z 584 (M+, BP); Anal. Calcd. for C42H36N2O: C, 86.27; H, 6.21; N, 4.79. Found: C, 86.04; H, 6.41; N, 4.65.

4.3. Preparation of Biphenyl-2-yl[Bis(4-Dimethylaminophenyl)Methylium]-2'-yl[Bis(4'-Methoxyphenyl)Methylium] Bis(Tetrafluoroborate) 2NO2+(BF4−)2

To a solution of diol 3NO (117 mg, 0.176 mmol) in n class="Chemical">DME (3 mL) was added propionic anhydride (0.6 mL) followed by 42% HBF4 (6.70 M, 90 μL, 0.60 mmol), and the mixture was heated at 80 °C for 1 h. By slow cooling to rt, dication salt 2NO2+(BF4−)2 was separated as a deep-violet solid (129 mg, y. 91%), which was filtered, washed with DME and dried in vacuo.

Mp 194–198 °C (decomp.); 1H NMR (400 MHz, n class="Chemical">CD3CN, 20 °C) δ/ppm 7.00–7.70 (16H, m), 6.92–6.98 (4H, AA’XX’), 6.62–6.73 (4H, AA’XX’), 4.03 (3H, s), 4.02 (3H, s), 3.22 (6H, s), 3.17 (6H, s); IR (KBr) 1580, 1506, 1464, 1372, 1278, 1220, 1160, 1124, 1084, 1062, 938, 912, 838, 722 cm−1; FAB-MS m/z 630 (M+, BP); Anal. Calcd. for C44H42N2O2B2F8+0.5H2O: C, 64.96; H, 5.33; N, 3.44. Found: C, 65.06; H, 5.40; N, 3.40.

4.4. Preparation of Biphenyl-2-yl[Bis(4-Dimethylaminophenyl)Methylium]-2'-yl[9-Xanthenylium] Bis(Tetrafluoroborate) 2NX2+(BF4−)2

To a solution of diol 3NX (70 mg, 11.3 μmol) in n class="Chemical">DME (3 mL) was added propionic anhydride (0.5 mL) followed by 42% HBF4 (50 μL, 33.5 μmol), and the mixture was heated at 80 °C for 1 h. By slow cooling to rt, dication salt 2NX2+(BF4−)2 was separated as a deep-green solid (80 mg, y. 93%), which was filtered, washed with DME, and dried in vacuo.

Mp 219–220 °C (decomp.); 1H NMR (400 MHz, n class="Chemical">CD3CN, 50 °C) δ/ppm 8.40 (2H, br.), 8.23 (2H, br. d, J = 8.5 Hz), 7.90 (2H, br. d, J = 8.5 Hz), 7.78–7.84 (3H, br. m), 7.46–7.56 (3H, br. m), 7.32 (2H, ddd, J = 7.8, 7.8, 1.0 Hz), 7.26–7.30 (1H, br. m), 6.85 (2H, br. d, J = 7.8 Hz), 6.20–7.20 (7H, br.), 3.30 (6H, br. s), 3.29 (6H, br. s); IR (KBr) 1622, 1584, 1506, 1374, 1174, 1084, 1036, 910, 762, 722 cm−1; FAB-MS m/z 584 (M+, BP); Anal. Calcd. for C42H36N2OB2F8: C, 66.52; H, 4.78; N, 3.69. Found: C, 66.64; H, 4.79; N, 3.76.

4.5. Oxidation to Biphenyl-2-yl[Bis(4-Dimethylaminophenyl)Methylium]-2'-yl[Bis(4'-Methoxyphenyl)Methylium] Bis(Hexachloroantimonate) 2NO2+(SbCl6−)2

To a solution of DHP n class="Chemical">1NO (10 mg, 15.9 μmol) in CH2Cl2 (10 mL) was added (4-BrC6H4)3N+•SbCl6− (26 mg, 31.8 μmol), and mixture was stirred for 20 min at rt. Deep-violet precipitates of 2NO2+(SbCl6−)2 (17 mg, y. 82%) were separated upon dilution with hexane (1 mL), which were filtered, washed with CH2Cl2 and dried in vacuo.

Mp >310 °C (decomp.); IR (KBr) 1580, 1438, 1372, 1280, 1160, 1004, 938, 912, 832, 722, 578 cm−1; Anal. Calcd. for n class="Chemical">C44H42N2O2Sb2Cl12: C, 40.66; H, 3.26; N, 2.16. Found: C, 40.76; H, 3.29; N, 2.26.

4.6. Oxidation to Biphenyl-2-yl[Bis(4-Dimethylaminophenyl)Methylium]-2'-yl[9-Xanthenylium] Bis(Hexachloroantimonate) 2NX2+(SbCl6−)2

To a solution of DHP n class="Chemical">1NX (5.0 mg, 8.6 μmol) in CH2Cl2 (2.5 mL) was added (4-BrC6H4)3N+•SbCl6− (14 mg, 17 μmol), and mixture was stirred for 10 min at rt. Deep-green precipitates of 2NX2+(SbCl6−)2 (8.5 mg, y. 79%) were separated upon dilution with hexane (1 mL), which were filtered, washed with CH2Cl2 and dried in vacuo.

Mp 203–210 °C (decomp.); IR (KBr) 1620, 1582, 1504, 1476, 1372, 1168, 940, 910, 832, 754, 722 cm−1; Anal. Calcd. for n class="Chemical">C42H36N2OSb2Cl12: C, 40.17; H, 2.89; N, 2.23. Found: C, 39.90; H, 3.05; N, 2.07.

4.7. Preparation of 2-[Bis(4-Dimethylaminophenyl)Hydroxymethyl]-2'-[Bis(4'-Methoxylphenyl)Hydroxymethyl]Biphenyl 3NO via Flow Microreactor Method

An integrated flow microreactor system consisting of four T-shaped micromixers (M1, M2, M3, and M4), four microtube reactors (R1, R2, R3, and R4), and five microtube units [P1 (inner diameter φ = 1000 μm, length l = 100 cm), P2 (φ = 1000 μm, l = 50 cm), P3 (φ = 1000 μm, l = 100 cm), P4 (φ = 1000 μm, l = 50 cm), and P5 (φ = 1000 μm, l = 100 cm)] was used. The whole flow microreactor system was dipped in a water bath (24 °C). A solution of n class="Chemical">2,2'-dibromobiphenyl (0.10 M) in THF (flow rate = 6.00 mL min−1) and a solution of BuLi (0.50 M) in hexane (flow rate = 1.20 mL min−1) were introduced to M1 (φ = 250 μm). The resulting solution was passed through R1 (φ = 500 μm, l = 3.5 cm) and was mixed with a solution of 4,4'-dimethoxybenzophenone 4O (0.20 M) in THF (flow rate = 3.00 mL min−1) in M2 (φ = 500 μm). The resulting solution was passed through R2 (φ = 1000 μm, l = 50 cm) and was introduced to M3 (φ = 500 μm) where the solution was mixed with a solution of BuLi (0.50 M) in hexane (flow rate = 1.44 mL min−1). The resulting solution was passed through R3 (φ = 1000 μm, l = 200 cm) and was introduced to M4 (φ = 500 μm) where the solution was mixed with a solution of 4,4'-bis(dimethylamino)benzophenone 4N (0.10 M) in THF (flow rate = 7.20 mL min−1). The resulting solution was passed through R4 (φ = 1000 μm, l = 200 cm). After a steady state was reached, the product solution was collected for 60 s and was treated with BuLi (1.67 M) in hexane (2.0 mL) to consume excess ketones and quench the reaction with water.

After diluted with H2O, the whole mixture was extracted with n class="Chemical">Et2O. The combined organic layers were washed with water and brine, and dried over anhydrous Na2SO4. After filtration, solvent was concentrated under reduced pressure. The residue was purified by column chromatography on silica gel (hexane/EtOAc = 3) to give 3NO (291 mg) as a colorless solid in 73% yield.

Mp 221–222 °C (decomp.); 1H NMR (400 MHz, n class="Chemical">CDCl3, 24 °C) δ/ppm 7.00–7.10 (9H, m), 6.92–6.96 (2H, br. d, J = 8.8 Hz), 6.74–6.86 (9H, m), 6.61–6.65 (4H, m), 6.19 (1H, dd, J = 8.6, 1.0 Hz), 6.04 (1H, dd, J = 8.6, 1.0 Hz), 5.23 (1H, s), 3.83 (3H, s), 3.78 (3H, s) 3.56 (1H, s), 2.95 (6H, s), 2.91 (6H, s); IR (KBr) 3550sh, 2900, 2832, 1612, 1512, 1466, 1352, 1298, 1250, 1174, 1062, 826, 762, 560 cm−1; FD-MS m/z (rel intensity) 664 (M+, 100), 646 (3); Anal. Calcd. for C44H44N2O4: C, 79.49; H, 6.67; N, 4.21. Found: C, 79.37; H, 6.80; N, 4.05.

4.8. Preparation of 2-[Bis(4-Dimethylaminophenyl)Hydroxymethyl]-2'-[Bis(4'-Methoxylphenyl)Hydroxymethyl]Biphenyl 3NO via Macro Batch Method

To a colorless solution of 2,2'-diiodobiphenyl (692 g, 1.70 mmol) in n class="Chemical">THF (12 mL) was added dropwise BuLi (1.70 mol dm−3 in hexane, 2.30 mL, 3.91 mmol) at −78 °C for 5 min under Ar, and the mixture was stirred for 45 min at this temperature. To the resultant suspension of 2,2'-dilithiobiphenyl was added a mixture of 4,4'-bis(dimethylamino)benzophenone 4N (406 mg, 1.51 mmol) and 4,4'-dimethoxybenzophenone 4O (364 mg, 1.50 mmol) in THF (30 mL) for 15 min. After stirring for 4 h, BuLi (1.70 mol dm−3 in hexane, 1.00 mL, 1.70 mmol) was added for 3 min to consume excess ketones. The resultant red solution was further stirred for 1 h and quenched by adding water. THF was evaporated, and the residue was extracted with benzene. The organic layer was washed with water and brine, and dried over Na2SO4. Evaporation of the solvent gave 1.09 g of oily material containing unsymmetric diol 3NO. Two symmetric diols, 3NN and 3OO, were also formed in this reaction. Chromatographic separation on SiO2 (hexane/AcOEt = 7/3) followed by crystallization from ether gave 3NO as colorless crystals (120 mg, y. 12%).

4.9. Preparation of 9-[2'-Bis(4-Dimethylaminophenyl)Hydoroxymethylbiphenyl-2-yl]-9-Hydroxyxanthene 3NX via Flow Microreactor Method

An integrated flow microreactor system consisting of four T-shaped micromixers (M1, M2, M3, and M4), four microtube reactors (R1, R2, R3, and R4), and five microtube units [P1 (inner diameter φ = 1000 μm, length l = 100 cm), P2 (φ = 1000 μm, l = 50 cm), P3 (φ = 1000 μm, l = 100 cm), P4 (φ = 1000 μm, l = 50 cm), and P5 (φ = 1000 μm, l = 100 cm)] was used. The whole flow microreactor system was dipped in a water bath (24 °C). A solution of n class="Chemical">2,2'-dibromobiphenyl (0.10 M) in THF (flow rate = 6.00 mL min−1) and a solution of BuLi (0.50 M) in hexane (flow rate = 1.20 mL min−1) were introduced to M1 (φ = 250 μm). The resulting solution was passed through R1 (φ = 500 μm, l = 3.5 cm) and was mixed with a solution of xanthone 4X (0.20 M) in THF (flow rate = 3.00 mL min−1) in M2 (φ = 500 μm). The resulting solution was passed through R2 (φ = 1000 μm, l = 50 cm) and was introduced to M3 (φ = 500 μm) where the solution was mixed with a solution of BuLi (0.50 M) in hexane (flow rate = 1.44 mL min−1). The resulting solution was passed through R3 (φ = 1000 μm, l = 200 cm) and was introduced to M4 (φ = 500 μm) where the solution was mixed with a solution of 4,4'-bis(dimethylamino)benzophenone 4N (0.10 M) in THF (flow rate = 7.20 mL min−1). The resulting solution was passed through R4 (φ = 1000 μm, l = 200 cm). After a steady state was reached, the product solution was collected for 60 s and was treated with BuLi (1.67 M) in hexane (2.0 mL) to consume excess ketones and quench the reaction with water. After diluted with H2O, the whole mixture was extracted with Et2O. The combined organic layers were washed with water and brine, and dried over anhydrous Na2SO4. After filtration, solvent was concentrated under reduced pressure. The residue was purified by column chromatography on silica gel (hexane/EtOAc = 5) to give 3NX (227 mg) as a colorless solid in 61% yield.

Mp 143–152 °C (decomp.); 1H NMR (400 MHz, n class="Chemical">CDCl3, 24 °C) δ/ppm 7.63 (1H, dd, J = 7.8, 1.5 Hz), 7.39 (1H, dd, J = 7.8, 1.5 Hz), 7.32 (1H, ddd, J = 7.8, 7.8, 1.5 Hz), 7.09–7.24 (6H, m), 7.02 (2H, AA’XX’), 6.95–7.00 (2H, m), 6.87 (2H, AA’XX’), 6.83–6.93 (3H, m), 6.72 (1H, ddd, J = 7.8, 7.8, 1.5 Hz), 6.64 (2H, AA’XX’), 6.59 (2H, AA’XX’), 6.18 (1H, dd, J = 7.8, 1.5 Hz), 5.72 (1H, m), 3.02 (1H, s), 2.94 (6H, s), 2.93 (6H, s); IR (KBr) 3048, 2796, 1612, 1520, 1478, 1450, 1354, 1240, 1190, 1154, 1032, 948, 816, 758 cm−1; FD-MS m/z 618 (M+, 100); Anal. Calcd. for C42H38N2O3: C, 81.53; H, 6.19; N, 4.53. Found: C, 81.60; H, 6.19; N, 4.40.

4.9. Preparation of 9-[2'-Bis(4-Dimethylaminophenyl)Hydoroxymethylbiphenyl-2-yl]-9-Hydroxyxanthene 3NX via Macro Batch Method

To a colorless solution of 2,2'-diiodobiphenyl (2.04 g, 5.02 mmol) in n class="Chemical">THF (20 mL) was added dropwise BuLi (1.47 mol dm−3 in hexane, 7.10 mL, 10.4 mmol) at 0 °C under Ar, and the mixture was stirred for 10 min at this temperature. To the resultant suspension of 2,2'-dilithiobiphenyl was added a mixture of 4,4'-bis(dimethylamino)benzophenone 4N (1.30 g, 4.85 mmol) and xanthone 4X (971 mg, 4.95 mmol) in THF (90 mL). After stirring for 2h at rt, the reaction was quenched by adding water. THF was evaporated, and the residue was extracted with benzene. The organic layer was washed with water and brine, and dried over Na2SO4. Evaporation of the solvent gave 3.66 g of oily material containing unsymmetric diol 3NX. Two symmetric diols, 3NN and 3XX, were also formed in this reaction. Chromatographic separation on SiO2 (AcOEt/hexane, 1/4–1/2) followed by crystallization from MeOH gave 3NX as colorless crystals (250 mg, y. 8.6%).

4.10. Preparation of 2-{Bis[3,4-Bis(Octyloxy)Phenyl]Hydroxymethyl}-2'-[Bis(4'-Methoxylphenyl)Hydroxymethyl]Biphenyl 3OO

An integrated flow microreactor system consisting of four T-shaped micromixers (M1, M2, M3, and M4), four microtube reactors (R1, R2, R3, and R4), and five microtube units [P1 (inner diameter φ = 1000 μm, length l = 100 cm), P2 (φ = 1000 μm, l = 50 cm), P3 (φ = 1000 μm, l = 100 cm), P4 (φ = 1000 μm, l = 50 cm), and P5 (φ = 1000 μm, l = 100 cm)] was used. The whole flow microreactor system was dipped in a water bath (24 °C). A solution of n class="Chemical">2,2'-dibromobiphenyl (0.10 M) in THF (flow rate = 6.00 mL min−1) and a solution of BuLi (0.50 M) in hexane (flow rate = 1.20 mL min−1) were introduced to M1 (φ = 250 μm). The resulting solution was passed through R1 (φ = 500 μm, l = 3.5 cm) and was mixed with a solution of 4,4'-dimethoxybenzophenone 4O (0.20 M) in THF (flow rate = 3.00 mL min−1) in M2 (φ = 500 μm). The resulting solution was passed through R2 (φ = 1000 μm, l = 50 cm) and was introduced to M3 (φ = 500 μm) where the solution was mixed with a solution of BuLi (0.50 M) in hexane (flow rate = 1.44 mL min−1). The resulting solution was passed through R3 (φ = 1000 μm, l = 200 cm) and was introduced to M4 (φ = 500 μm) where the solution was mixed with a solution of 3,3',4,4'-tetrakis(octyloxy)benzophenone 4O (0.10 M) in THF (flow rate = 7.20 mL min−1). The resulting solution was passed through R4 (φ = 1000 μm, l = 200 cm). After a steady state was reached, the product solution was collected for 120 s and was treated with H2O to quench the reaction.

After diluted with H2O, the whole mixture was extracted with n class="Chemical">CH2Cl2. The combined organic layers were washed with water and brine, and dried over anhydrous Na2SO4. After filtration, solvent was concentrated under reduced pressure. The residue was purified by column chromatography on silica gel (CH2Cl2/hexane = 3) to give 3OO (889 mg) as a colorless oil in 68% yield.

1H NMR (300 MHz, n class="Chemical">CDCl3) δ/ppm 7.11–7.00 (6H, m), 6.85–6.72 (12H, m), 6.62 (1H, dd, J = 8.4, 1.8 Hz), 6.52 (1H, dd, J = 8.4, 1.8 Hz), 6.14–6.08 (2H, m), 4.39 (1H, s), 4.19 (1H,s), 4.00 (2H, t, J = 6.6 Hz), 3.97 (2H, t, J = 6.6 Hz), 3.90–3.74 (10H, m), 1.89–1.63 (8H, m), 1.53–1.18 (40H, m), 0.94–0.82 (12H, m); 13C NMR (100 MHz, CDCl3) δ/ppm 158.53, 158.45, 148.35, 148.31, 148.26, 147.75, 143.94, 143.87, 141.12, 140.88, 138.98, 138.80, 131.58, 131.33, 130.31, 130.18, 129.64, 128.53, 125.98, 125.93, 125.79, 121.16, 120.34, 115.04, 113.10, 112.97, 112.87, 112.57, 83.35, 83.17, 69.27, 69.20, 69.12, 68.95, 55.18, 55.15, 31.78, 29.41, 29.35, 29.23, 29.13, 25.98, 25.94, 22.62, 14.05; IR (neat) 3538, 3397, 3053, 2953, 2927, 2856, 1607, 1583, 1509, 1468, 1442, 1435, 1417, 1379, 1298, 1252, 1175, 1162, 1137, 1064, 1037, 1064, 1037, 828, 808, 789, 756 cm−1; FD-MS m/z 1091 (M+, 83), 1090 (BP); FD-HR-MS (FD) Calcd. for C72H98O8: 1090.7262 Found: 1090.7244.

4.11. Preparation of 2-{Bis[3,4-Bis(Hexadecyloxy)Phenyl]Hydroxymethyl}-2'-[Bis(4'-Methoxylphenyl)Hydroxymethyl]Biphenyl 3OO

An integrated flow microreactor system consisting of four T-shaped micromixers (M1, M2, M3, and M4), four microtube reactors (R1, R2, R3, and R4), and five microtube units [P1 (inner diameter φ = 1000 μm, length l = 100 cm), P2 (φ = 1000 μm, l = 50 cm), P3 (φ = 1000 μm, l = 100 cm), P4 (φ = 1000 μm, l = 50 cm), and P5 (φ = 1000 μm, l = 100 cm)] was used. The whole flow microreactor system was dipped in a water bath (24 °C). A solution of n class="Chemical">2,2'-dibromobiphenyl (0.10 M) in THF (flow rate = 6.00 mL min−1) and a solution of BuLi (0.50 M) in hexane (flow rate = 1.20 mL min−1) were introduced to M1 (φ = 250 μm). The resulting solution was passed through R1 (φ = 500 μm, l = 3.5 cm) and was mixed with a solution of 4,4'-dimethoxybenzophenone 4O (0.20 M) in THF (flow rate = 3.00 mL min−1) in M2 (φ = 500 μm). The resulting solution was passed through R2 (φ = 1000 μm, l = 50 cm) and was introduced to M3 (φ = 500 μm) where the solution was mixed with a solution of BuLi (0.50 M) in hexane (flow rate = 1.44 mL min−1). The resulting solution was passed through R3 (φ = 1000 μm, l = 200 cm) and was introduced to M4 (φ = 500 μm) where the solution was mixed with a solution of 3,3',4,4'-tetrakis(hexadecyloxy)benzophenone 4O (0.10 M) in toluene (flow rate = 7.20 mL min−1). The resulting solution was passed through R4 (φ = 1000 μm, l = 200 cm). After a steady state was reached, the product solution was collected for 60 s and was treated with H2O to quench the reaction.

After diluted with H2O, the whole mixture was extracted with n class="Chemical">CH2Cl2. The combined organic layers were washed with water and brine, and dried over anhydrous Na2SO4. After filtration, solvent was concentrated under reduced pressure. The residue was purified by column chromatography on silica gel (CH2Cl2/hexane = 2) and GPC separation (1+2H) to give 3OO (889 mg) as a colorless oil in 68% yield, which was solidified upon standing.

Mp 60–62 °C; 1H NMR (300 MHz, n class="Chemical">CDCl3) δ/ppm 7.11–6.99 (6H, m), 6.85–6.72 (12H, m), 6.63 (1H, dd, J = 8.4, 1.8 Hz), 6.52 (1H, dd, J = 8.4, 1.8 Hz), 6.14–6.08 (2H, m), 4.39 (1H, s), 4.19 (1H,s), 4.00 (2H, t, J = 6.6 Hz), 3.96 (2H, t, J = 6.6 Hz), 3.90–3.73 (10H, m), 1.89–1.62 (8H, m), 1.52–1.18 (104H, m), 0.92-0.82 (12H, m); 13C NMR (100 MHz, CDCl3) δ/ppm 158.56, 158.50, 148.40, 148.36, 148.28, 147.79, 143.97, 143.90, 141.16, 140.91, 140.65, 139.02, 138.85, 131.61, 131.36, 130.34, 130.21, 129.67, 128.57, 126.02, 125.97, 125.85, 121.20, 120.37, 115.11, 113.15, 113.00, 112.92, 112.62, 83.38, 83.20, 69.32, 69.25, 69.17, 69.02, 55.23, 55.20, 31.92, 29.71, 29.66, 29.51, 29.46, 29.37, 29.30, 29.20, 26.06, 26.02, 25.99, 22.68, 14.10; IR (KBr) 3382, 3051, 2919, 2850, 1607, 1510, 1468, 1434, 1416, 1389, 1302, 1254, 1173, 1138, 1064, 1039, 827, 810, 760, 721, 560 cm−1; FD-MS m/z 1540 (BP), 1539 (M+, 82); FD-HR-MS (FD) Calcd. for C104H162O8: 1539.2270 Found: 1539.2297.

4.12. Preparation of 3,3',4,4'-Tetrakis(Octyloxy)Benzophenone 4O

To a solution of 4-bromo-1,2-bis(octyloxy)n class="Chemical">benzene (4.14 g, 10.0 mmol) in 50 mL of dry ether was added BuLi in hexane(1.57 M, 6.40 mL, 10.0 mmol) at 22 °C under Ar, and the mixture was stirred for 1 h. To the suspension was added N-carboethoxypiperidine (770 µL, 4.99 mmol) and the mixture was stirred at 23 °C for 20 h. After diluted with 3 M HCl aq., the whole mixture was extracted with CH2Cl2. The combined organic layers were washed with 3 M HCl aq. and 1 M NaOH aq., and dried over anhydrous MgSO4. After filtration, solvent was concentrated under reduced pressure. The residue was purified by column chromatography on silica gel (CH2Cl2/hexane = 2) to give 4O (2.92 g) as a colorless solid in 84% yield.

Mp 58.5–59.5°C; 1H NMR (300 MHz, n class="Chemical">CDCl3) δ/ppm 7.40 (2H, d, J = 1.8 Hz), 7.35 (2H, dd, J = 8.4, 1.8 Hz), 6.88 (2H, d, J = 8.4 Hz), 4.07 (4H, t, J = 6.6 Hz), 4.04 (4H, t, J = 6.6 Hz), 1.93–1.77 (8H, m), 1.55–1.21 (40H, m), 0.93–0.82 (12H, m); 13C NMR (100 MHz, CDCl3) δ/ppm 194.63, 152.74, 148.64, 130.69, 124.67, 114.65, 111.50, 69.28, 69.07, 31.82, 29.35, 29.27, 29.20, 29.10, 25.99, 22.67, 14.10; IR (KBr) 2955, 2920, 2873, 2852, 1665, 1597, 1581, 1518, 1469, 1413, 1390, 1343, 1301, 1265, 1237, 1200, 1127, 1023, 1011, 964, 847, 821, 753, 721, 626 cm−1; FD-MS m/z 695 (M+, BP); Anal. Calcd. for C45H74O5: C, 77.76; H, 10.73. Found: C, 77.76; H, 10.71%.

4.13. Preparation of 3,3',4,4'-Tetrakis(Hexadecyloxy)Benzophenone 4O

To a solution of 4-bromo-1,2-bis(hexadecyloxy)benzene (5.01 g, 7.85 mmol) in 25 mL of dry ether and 25 mL of dry n class="Chemical">hexane was added BuLi in hexane (1.57 M, 5.00 mL, 7.85 mmol) at 23 °C under Ar, and the mixture was stirred for 1 h. To the suspension was added N-carboethoxypiperidine (600 µL, 3.89 mmol) and the mixture was stirred at 24 °C for 23 h. After diluted with 3 M HCl aq., the whole mixture was extracted with CH2Cl2. The combined organic layers were washed with 3 M HCl aq. and 1 M NaOH aq., and dried over anhydrous MgSO4. After filtration, solvent was concentrated under reduced pressure. The residue was purified by column chromatography on silica gel (CH2Cl2/hexane = 1) to give 4O (3.56 g) as a colorless solid in 80% yield.

Mp 81.5–83.0 °C; 1H NMR (300 MHz, n class="Chemical">CDCl3) δ/ppm 7.40 (2H, d, J = 1.8 Hz), 7.34 (2H, dd, J = 8.4, 1.8 Hz), 6.88 (2H, d, J = 8.4 Hz), 4.07 (4H, t, J = 6.6 Hz), 4.03 (4H, t, J = 6.6 Hz), 1.92–1.76 (8H, m), 1.53–1.18 (104H, m), 0.92–0.82 (12H, m); 13C NMR (100 MHz, CDCl3) δ/ppm 194.61, 152.74, 148.64, 130.69, 124.67, 114.65, 111.49, 69.28, 69.07, 31.93, 29.71, 29.64, 29.43, 29.37, 29.20, 29.12, 26.01, 22.68, 14.11; IR (KBr) 2956, 2917, 2849, 1661, 1597, 1579, 1518, 1468, 1432, 1414, 1392, 1342, 1266, 1237, 1200, 1125, 1030, 1016, 850, 754, 721, 625 cm−1; FD-MS m/z 1143 (M+, BP); Anal. Calcd. for C77H138O5: C, 80.85; H, 12.16. Found: C, 80.73; H, 12.15%.

4.14. Preparation of 4-Bromo-1,2-Bis(Hexadecyloxy)Benzene

To a solution of 1,2-bis(hexadecyloxy)benzene (14.9 g, 26.7 mmol) in 200 mL of dry n class="Chemical">CH2Cl2 was added N-bromosuccinimide (4.75 g, 26.7 mmol) in dry MeCN 70 mL at 23 °C under Ar, and the mixture was stirred for 20 h. After diluted with water, the whole mixture was extracted with CH2Cl2. The combined organic layers were washed with 10% Na2S2O3 aq. and brine, and dried over anhydrous MgSO4. After filtration, solvent was concentrated under reduced pressure. The residue was purified by column chromatography on silica gel (hexane/EtOAc = 200 to 100) to give 4-bromo-1,2-bis(hexadecyloxy)benzene (16.8 g) as a colorless solid in 99% yield.

Mp 62.5–63.5 °C; 1H NMR (300 MHz, n class="Chemical">CDCl3) δ/ppm 7.00–6.94 (2H, m), 6.72 (1H, d, J = 9.1 Hz), 3.95 (2H, t, J = 6.6 Hz), 3.94 (2H, t, J = 6.6 Hz), 1.86–1.72 (4H, m), 1.52–1.17 (52H, m), 0.92–0.84 (6H, m); 13C NMR (100 MHz, CDCl3) δ/ppm 150.06, 148.38, 123.42, 116.95, 115.17, 112.79, 69.53, 69.38, 31.93, 29.71, 29.63, 29.38, 29.23, 29.13, 25.99, 22.70, 14.11; IR (KBr) 2917, 2848, 1588, 1509, 1503, 1468, 1446, 1434, 1392, 1324, 1258, 1220, 1132, 1066, 1014, 955, 865, 842, 826, 800, 722, 644, 576 cm−1; FD-MS m/z (relative intensity) 638 (M+, 35), 636 (M+, 35), 559 (BP); Anal. Calcd. for C38H69O2Br: C, 71.55; H, 10.90. Found: C, 71.37; H, 10.80%.

4.15. Measurement of Redox Potentials

All the redox potentials (Eox and Ered) were measured under argon atmosphere by cyclic voltammetry in n class="Chemical">CH2Cl2 containing 0.1 M Bu4NBF4 as a supporting electrolyte. All the values are reported in E/V vs. SCE, and Pt wire was used as the working electrode. In the case of irreversible waves, half-wave potentials were estimated from the peak potentials as Eox = Epa (anodic peak potential) −0.03 V, and Ered = Epc (cathodic peak potential) +0.03 V.

4.16. X-Ray Structural Analyses

Unsymmetric DHP n class="Chemical">1NX: C42H36N2O, M 584.76, 0.60 × 0.10 × 0.05 mm, orthorhombic, space group P212121, a = 10.4511(4), b = 14.0601(7), c = 20.771(1) Å, V = 3052.2(3) Å [3,4], and Dcalcd (Z = 4) = 1.272 g cm−3. Numerical absorption correction was applied (μ = 0.76 cm−1). Data collection was performed on a Rigaku Mercury CCD camera appararus (Mo-Kα radiation, λ = 0.71069 Å, 50 kV, 50 mA) at 203 K. The structure was solved by the direct method and refined by full-matrix least-squares method on F with anisotropic temperature factors for non-hydrogen atoms. Hydrogen atoms were located at the calculated positions. The final R and Rw values are 0.044 and 0.049 for 407 parameters and 2835 reflections with I > 3σ (I) (independent reflections, 3625; 2θmax = 53.5°). The GOF indicator is 1.20. Residual electron density is 0.16 Å−3. CCDC 182/1003