Highly Luminescent Probes from Terpyridine, Phenanthroline, and Pyrromethene·BF₂ Auxiliaries

Abstract

The synthesis of novel bodipy based fluorophores appended to pyridine (py), terpyridine (terpy), and phenanthroline (phen) cores has been performed using three different methods. The most effective and reliable method consists in cross coupling an iodo functionalized bodipy with ethynyl grafted oligopyridines. The cross coupling the other way around from an ethynyl functionalized bodipy is less effective due to a homocoupling reaction leading to the butadiyne bridged species. For the less stable alkynes, a one-pot protocol, under phase transfer conditions, using the trimethylsilyl-protected alkynes has been finalized. Compounds exhibit very strong absorption and emission properties in the visible.

indacene - bipyridine - fluorescent dyes - terpyridine - alkyne - palladium coupling

References

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A representative experimental procedure is given for the preparation and purification of compound 10 using the phase transfer conditions sketched in Scheme [4] . A benzene (15 mL)/H₂O (10 mL) biphasic mixture containing 5,5′-bis-trimethylsilylethynyl-2:2′;6′:2′′-terpyridine (14; 0.042 g, 0.099 mmol), 1 (0.100 g, 0.198 mmol), NaOH (0.04 g, 0.99 mmol), Et₃BzNCl (0.001 g, 0.006 mmol) was strongly degassed with argon. To this solution Pd(PPh₃)₄ (0.014 g, 0.012 mmol) and CuI (0.0025 g, 0.01 mmol) was then added and the reaction was heated under argon, at 60 °C during 1 d. The benzene was then removed, H₂O added, and the compound extracted with CH₂Cl₂. The organic fractions were dried over MgSO₄, and a chromatography on alumina (Al₂O₃, CH₂Cl₂/hexane, 1:1, v:v) afforded the pure compound as a red powder (0.089 g, 87%).¹H NMR (300.1 MHz, CDCl₃): δ = 0.99 (t, 12 H, ³ J = 7.5 Hz, CH₃), 1.35 (s, 12 H), 2.31 (q, 8 H, ³ J = 7.5 Hz, CH₂), 2.54 (s, 12 H), 7.56 (ABsys, 8 H, J _AB = 8.2 Hz, ν₀δ = 114.5 Hz), 7.96-8.02 (m, 3 H), 8.51 (d, 2 H, ³ J = 7.9 Hz), 8.66 (d, 2 H, ³ J = 8.3 Hz), 8.87 (d, 2 H, ⁴ J = 2.1 Hz).¹¹B NMR (128.4 MHz, CDCl₃): δ = 3.86 (t,
J _B-F = 33.30 Hz).UV/Vis (CH₂Cl₂, 23 °C): λ_max (ε, M^-1
cm^-1) = 347 (140,000), 497 (sh, 86,000), 526 (225,000). IR (KBr): 3437, 2920, 1620 (br, ν_C=N), 1594, 1384, 1115 cm^-1. MS (FAB⁺, mNBA): m/z (%) = 1037 (100) [M]⁺, 1018 (20) [M - F]⁺. Anal. Calcd for C₆₅H₆₁B₂F₄N₇: C, 75.22; H, 5.92; N, 9.45; Found C, 75.05; H, 5.77; N, 9.22.