| ¹H NMR (toluene-d₈) | 14.11 ppm (s, 2H, OH), 8.14 ppm (s, 2H, NH), 7.59 ppm (s, 2H), 7.22 ppm (s, 2H) 7.12ppm (s, 2H), 1.67 ppm (s, 18H), 1.37ppm (s, 18H) |
|---|---|
| LR-MALDI-TOF | m/z calcd. for C₃₆H₄₆O₂N₄+H 567.37, obsd. 567.37 |
| HR-ESI-MS | m/z calcd. for C₃₆H₄₆O₂N₄+H 567.3694, obsd. 567.3692 (-0.3143 ppm) |
| MALDI-TOF, base peak | m/z = 567.37; isotopic distribution corresponds to [C₃₆H₄₆N₄O₂+H]⁺ |
| MALDI-TOF, small peak | m/z = 551.32; neutral loss of one methyl moiety from one t-butyl group |
| NMR in polar solvents such as THF | Cis-/trans-tautomerization observed |
| NMR in nonpolar solvents such as DCM and toluene | Only the trans-tautomer observed |
| Variable-temperature ¹H NMR (1,1,2,2-tetrachloroethane-d₂) | Roto-isomerization of the phenols |
| Variable-temperature ¹H NMR temperatures | 263, 273, 283, 293, 303, 313, 323, 333, and 343 K |
| ¹H NMR (tetrahydrofuran-d₈), unlabeled low-intensity peaks | Cis-rotamer present at approximately 15 % relative to the trans-rotamer |
| NOESY (tetrahydrofuran-d₈) | NOE interactions of phenolic-imidazolic-benzilic protons in both cis- and trans-imidazole rotamers |
| ¹³C NMR (tetrahydrofuran-d₈), t-butyl-group doublet structure | Due to roto-isomerization with respect to the phenol OH group |
| HSQC (tetrahydrofuran-d₈), aliphatic-region doublet structure along the proton axis | Due to roto-isomerization of the t-butyl groups |
| ¹H NMR (dichloromethane-d₂), OH/NH protons after isotope-reagent addition | Lost, indicating exchange for deuterons |
| ¹H NMR, phenol H peaks | Shifted downfield in several solvents, consistent with intramolecular bond |
| ¹H NMR, imidazole N-H peaks | Greater solvent dependence |
Caius Jacott, Boris V. Kramar, Peter J. Bonitatibus, Jr., Peter H. Dinolfo. “Proton-coupled intervalence charge-transfer in a mixed-valent phenol-benzimidazole dimer.” ChemRxiv (). https://doi.org/10.26434/chemrxiv.15007495/v1
| Empirical formula | C₂₁H₃₀N₃O₂ |
|---|---|
| Formula weight | 356.49 |
| Temperature | 93.15 K |
| Crystal system | Monoclinic |
| Space group | C2/m |
| a | 19.1188(7) Å |
| b | 6.9643(3) Å |
| c | 15.3809(6) Å |
| α | 90° |
| β | 97.786(3)° |
| γ | 90° |
| Volume | 2029.07(14) ų |
| Z | 4 |
| Z′ | 0.5 |
| ρcalc | 1.167 g/cm³ |
| μ | 0.076 mm⁻¹ |
| R1 (2387 reflections) | 0.0404 |
| wR2 (all data) | 0.1173 |
| GOF on F2 | 1.040 |
| Single-crystal XRD, phenol protons | Resolvable and hydrogen-bonded to the benzimidazoles |
| Single-crystal XRD, phenol-ring dihedral angles with the central benzobisimidazole core | 0° |
| Single-crystal XRD, phenol O to imidazole N distance | 2.553 Å |
| Single-crystal XRD, phenol center-to-center distance | 12.18 Å |
| Single-crystal XRD, O to O distance | 10.58 Å |
| ORTEP, phenolic protons | Resolved |
| ORTEP, other proton positions | Inferred |
| ORTEP, N,N-dimethylformamide disorder | Rotation of 180° |
| ORTEP, t-butyl methyl-moiety disorder | Rocked back and forth by approximately 5° |
| Fluorescence emission band | Broad and featureless, with a Stokes shift of approximately 100 nm |
|---|---|
| ESIPT fluorescence band | Approximately 510 nm |
| Fluorescence emission band | Dramatic hypsochromic shift with vibronic structure indicating a change to a π→π* transition |
|---|
| ESIPT emission band | Significantly quenched |
|---|
| CV (0.1 M TBAPF6), first quasi-reversible single-electron oxidation, E1/2 | +0.92 V vs SCE |
|---|---|
| CV (0.1 M TBAPF6), second quasi-reversible single-electron oxidation, E1/2 | +1.15 V vs SCE |
| Difference in half-wave potentials | 230 mV |
| Comproportionation constant | 1.3x10⁴ |
| Scan rates | 100, 250, 500, and 750 mV s⁻¹ |
| First oxidation/reduction, isolated first-couple scan at 100 mV s⁻¹ | Reversibility was not lost due to the second oxidation |
| First oxidation/reduction, approximate potential | Approximately 0.9 V vs SCE |
| First oxidation, ipeak versus square root of scan rate | y = 1.05155E−6x + 1.53941E−5; R² = 0.99630 |
| First reduction, ipeak versus square root of scan rate | y = −6.89922E−7x − 6.91353E−6; R² = 0.99667 |
| First oxidation/reduction assignment | Quasi-reversible behavior |
| Second oxidation/reduction, approximate potential | Approximately 1.1 V vs SCE |
| Second oxidation, ipeak versus square root of scan rate | y = 1.92425E−6x + 2.23439E−5; R² = 0.99929 |
| Second reduction, ipeak versus square root of scan rate | y = −4.32415E−6x − 2.08922E−5; R² = 0.99741 |
| Second oxidation/reduction assignment | Quasi-reversible behavior |
| First reversible redox couple, E1/2 | +0.28 V vs SCE |
|---|---|
| Second reversible redox couple, E1/2 | +0.55 V vs SCE |
| Comproportionation constant | 3.7x10⁴ |
| Scan rates | 100, 250, 500, and 750 mV s⁻¹ |
| First oxidation/reduction, approximate potential | Approximately 0.3 V vs SCE |
| First oxidation, ipeak versus square root of scan rate | y = 1.53949E−5x + 9.52995E−6; R² = 0.90959 |
| First reduction, ipeak versus square root of scan rate | y = −8.14900E−6x − 4.98926E−7; R² = 0.88752 |
| First oxidation/reduction assignment | Quasi-reversible behavior |
| Second oxidation/reduction, approximate potential | Approximately 0.6 V vs SCE |
| Second oxidation, ipeak versus square root of scan rate | y = 6.90623E−6x + 2.10644E−6; R² = 0.74559 |
| Second reduction, ipeak versus square root of scan rate | y = −6.45426E−6x − 4.25619E−6; R² = 0.85590 |
| Second oxidation/reduction assignment | Quasi-reversible behavior, with less reversibility than the first oxidation/reduction |
| Benzimidazole N-H stretching band | 3415 cm⁻¹; decreased with each sequential oxidation |
|---|---|
| t-d(PI)B1+, new N-H stretching band | 3325 cm⁻¹; assigned to benzimidazolium ions |
| t-d(PI)B2+, shifted N-H stretching band | 3310 cm⁻¹; assigned to benzimidazolium ions |
| Fingerprint region | Changes in the imidazole N-H bending modes |
| First oxidation, author-assigned protonation state | (PhOH)(ImH) |
| t-d(PI)B1+, N-H vibrational modes | Combination of imidazole and imidazolium modes |
| Second oxidation, author-assigned protonation state | (ImH)2 |
| Comparison assignment | Indicated formation of a di-imidazolium cation |
|---|---|
| Red trace below 1500 cm⁻¹ | Vibrations are solvent absorbances |
| Blue trace | Non-correlated vibrations are due to tetrabutylammonium hexafluorophosphate electrolyte |
| t-d(PI)B, electronic absorption | Dominated by π→π* transitions between 300–400 nm |
|---|---|
| t-d(PI)B1+ and t-d(PI)B2+, new transitions | Approximately 450 nm; assigned to phenoxide radicals |
| t-d(PI)B1+ and t-d(PI)B2+, 300–400 nm bands | Decreased |
| t-d(PI)B1+, broad absorption band | Centered at 1000 nm; absent from t-d(PI)B and t-d(PI)B2+; assigned to intervalence charge transfer |
| Deuterated mixed-valence-state absorption spectrum | Very similar to the protonated mixed-valence-state spectrum |
|---|---|
| IVCT-band energy after deuterium exchange | Shifted to higher energy by approximately 80 cm⁻¹ |
| IVCT-band intensity after deuterium exchange | Reduced by approximately half |
| Apparent IVCT isotope effect | Approximately 1.8 |