Synthesis of Bisisoindolomethene Dyes Bearing Anisole or Ethylthiophene Residues for Red and Near-IR Fluorescence

Abstract

New difluorobora-diisoindolomethenes dyes were synthesized from carbohydrazide and o-hydroxy-acetophenone derivatives bearing phenyl, p-anisole or ethylthiophene substituents. The nature of the substituents allows modulating the fluorescence from 650 nm to 780 nm. Replacement of the fluoro ligands by ethynyl-aryl residues is feasible using Grignard reagents. Standard fluorescence studies prove that very efficient energy transfer, from the pyrene moiety linked to the boron center to the boradiazaindacene, is effective in providing large virtual Stokes shifts.

Key words

diisoindolomethene - ethynyl-boron - pyrene - fluorescence - energy transfer

References and Notes

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16

General Procedure for Fluorine Replacement
A Schlenk flask was charged with the ethynyl derivative and anhyd THF. A solution of EtMgBr (1 M in THF) was then added dropwise and the mixture was stirred at 50 °C for 2 h. The mixture was then added at 25 °C via a cannula to a solution of 4a-c in anhyd THF. The mixture was stirred at 70 °C for 16 h and the solvent was removed by rotary evaporation. The residue was treated with H₂O and extracted with CH₂Cl₂. The organic extracts were washed with H₂O, and dried over MgSO₄. The solvent was removed, and the residue was purified by chromatography.
Compound 5a
Prepared following general procedure from 4a (100 mg, 0.22 mmol), 1-ethynyltoluene (104 mg, 0.9 mmol), EtMgBr (0.41 mL, 0.41 mmol, 1 M in THF), THF (8 mL). Chromatography (silica gel, CH₂Cl₂-cyclohexane, 30:70 to 50:50) gave 5a as a blue crystalline powder (60 mg, 42%). ¹H NMR (CDCl₃, 300 MHz): δ = 8.20 (d, 4 H, J = 6.6 Hz), 7.96 (d, 4 H, J = 6.0 Hz), 7.92 (s, 1 H), 7.61-7.39 (m, 11 H), 7.22-7.18 (m, 1 H), 6.88 (AB system, 8 H, J _AB = 8.0 Hz, Δδ_AB = 24.3 Hz), 2.27 (s, 6 H). ¹³C NMR (CDCl₃, 75 MHz): δ = 151.2, 136.8, 133.7, 132.4, 131.3, 130.9, 130.3, 128.3, 128.1, 127.7, 127.6, 124.6, 123.0, 122.4, 121.7, 118.4, 115.8, 98.6, 21.3. ¹¹B NMR (CDCl₃, 128 MHz): δ = -7.14 (s). UV/Vis (CH₂Cl₂): λ (ε, M^-1 cm^-1) = 632 (82500), 588 (27000, sh), 269 (12000) nm. MS (ES): m/z (nature of the peak, relative intensity) = 637.1 (100) [M + H]⁺. Anal. Calcd for C₄₇H₃₃BN₂: C, 88.68; H, 5.23; N, 4.40. Found: C, 88.40; H, 4.95; N, 4.18.

17

Crystal Data for 4a at 293 K: C₂₉H₁₉BF₂N₂, M = 444.27, triclinic, space group P-1, a = 7.310 (5) Å, b = 11.771 (5) Å, c = 13.336 (5) Å, α = 86.84 (0)°, β = 79.14 (0)°, γ = 89.79 (0)°, V = 1125.2 (10) ų, Z = 2, λ = 0.7107 Å, D _c = 1.311 g cm^-3, µ = 0.057 mm^-1, 24014 reflections collected with θ £ 26.0°, 4363 unique, R(int) = 0.0202, and 3343 observed reflections [ I ³ 2σ(I)], 308 parameters, R1 = 0.0396, wR2 = 0.1012 refined on F ². CCDC 637684.

18

Crystal Data for 5a at 293 K: C₄₇H₃₃BN₂, M = 636.56, triclinic, space group P-1, a = 11.119 (4) Å, b = 11.674 (3) Å, c = 15.572 (4) Å, α = 78.73 (2)°, β = 73.51 (2)°, γ = 66.73 (2)°, V = 1772.5 (9) ų, Z = 2, λ = 0.7107 Å, D _c = 1.193 g cm^-3, µ = 0.068 mm^-1, 12226 reflections collected with θ < 27.5°, 8071 unique, R(int) = 0.0241, and 5025 observed reflections [ I ³ 2σ(I)], 453 parameters, R1 = 0.0571, wR2 = 0.1438 refined on F ². CCDC 623954.

19

Crystal Data for 6a at 293 K: [C₄₉H₃₃BN₂, 0.5 × (C₆H₁₂, C₂H₃N)], M = 723.19, triclinic, space group P-1, a = 11.294 (4) Å, b = 13.299 (3) Å, c = 14.735 (4) Å, α = 101.78 (2)°, β = 110.03 (2)°, γ = 102.17 (2)°, V = 1938.4 (10) ų, Z = 2, λ = 0.7107 Å, D _c = 1.239 g cm^-3, µ = 0.071 mm^-1, 10488 reflections collected with θ < 22.4°, 4585 unique, R(int) = 0.0351, and 3135 observed reflections [ I ³ 2σ(I)], 470 parameters, R1 = 0.0649, wR2 = 0.1879 refined on F ². SQUEEZE macro within PLATON was used to take disordered solvent molecules (half a molecule of cyclohexane and half a molecule of MeCN in the asymmetric unit) into account during the structure refinement process. CCDC 623955.