4,5,5-Trimethyl-2,5-dihydrofuran-Based Electron-Withdrawing Groups for NIR-Emitting Push–Pull Dipolar Fluorophores

Abstract

In the context of molecular engineering of push–pull dipolar dyes, we introduce a structural modification of the well-known electron-accepting group 2-dicyanomethylidene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran (TCF). Introduction of a (benzo­[d]­thiazol-2-yl) moiety failed, and unexpected structures were obtained. On the other hand, phenylthio and phenylsulfonyl entities were successfully introduced at position 3 of the 2-(dicyanomethylidene)-2,5-dihydrofuran ring, giving access to new electron-acceptor groups and dipolar fluorophores displaying near-infrared emission in solution or in the solid state, brighter than their TCF analogues.

Push–Pull Dyes for Yellow to NIR Emitting Electrochemical Cells

“…All dyes in this study showed strong solvatochromism due to their strong push-pull character ( Figure S4, Supporting Information for dyes IV and V; for I-III, [30] [31] [31] ). The Lippert-Mataga model was used to fit the Stokes shifts of the dyes to the solvent orientation polarizability (Δf) ( Figure S5 and Table S2, Supporting Information).…”

“…DPF dyes (I-III) undergo ICT though a fluorene π-bridge between diphenylamine and an acceptor group: 1,3-indandione (I), 2-(dicyanomethylene)-3-phenylthio-4,5,5-trimethyl-2,5-dihydrofuran (II) and 2-(dicyanomethylene)-3-phenylsulfonyl-4,5,5trimethyl-2,5-dihydro-furan (III). [30,31] Dye IV contains N- (2-methoxyphenyl)carbazole as the donor and the same acceptor as II. Finally, dye V contains N-ethylcarbazole as a donor and 4,5,5′-trimethyl-3-(phenylsulfonyl)furan-2(5H)-one as an acceptor.…”

“…The synthesis of the other dyes, also by Knoevenagel condensations, was previously described. [30,31,33] The thermal properties of the dyes showed high melting points (>225 °C) as well as excellent thermal stability (>290 °C), as determined by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) ( Figure S2 and Table S1, Supporting Information). In particular, dyes I and II showed the best thermal stability and the highest thermal degradation temperature for 5% weight loss (T 95% , ≈340 °C).…”

Merocyanine Dyes with Extended Polymethine Chains by Simple Two-Step Condensation Sequence

“…14 Nevertheless, elongated polymethine chains have recently attracted considerable interest because several groups could show that merocyanine dyes with extended polymethine chains (mostly consisting of three double bonds) may have better fluorescence properties compared to their homologues with shorter polymethine chains. [15][16][17] Better alignments could also be realized for elongated molecules in liquid-crystalline hosts, which is of interest for polarizers. 18 Furthermore, with longer polymethine chains, the near-infrared (NIR) spectral range can be reached, which is of interest for biomolecular imaging applications.…”

Synthesis, Characterization and Unusual Near-Infrared Luminescence of 1,1,4,4-Tetracyanobutadienes

“…Such a finding suggests that TCBDs present surprising potentialities as NIR emitters, which find various applications such as NIR-OLED 30 or biological imaging, as these wavelengths allow for improved penetration depths compared to visible-wavelength imaging. 28 Furthermore, while the development of small organic molecules as NIR-I dyes undoubtedly remains a challenging task, 31 the design of efficient fluorophores reaching the second near-infrared window (NIR-II, 1000-1700 nm) is an emerging field that may provide considerable advance in deep-tissue imaging. 29 Interestingly, considering the rather broad signal shape of compounds 1 and 2 (with a full width at half maximum of 195 nm in both cases), a significant portion of the PL bands is located in the NIR-II region: this particular PL accounts for 10% of the emission of 1, and 30% of that of 2.…”