Unprecedented Nucleophilic Attack of Piperidine on the Electron Acceptor during the Synthesis of Push‐Pull Dyes by a Knoevenagel Reaction

Abstract

An unprecedented nucleophilic addition of piperidine on an electron acceptor, namely, 2‐(3‐oxo‐2,3‐dihydro‐1H‐cyclopenta[b]naphthalen‐1‐ylidene)malononitrile is reported. This unexpected behavior was observed during the synthesis of push‐pull dyes using the classical Knoevenagel reaction. To overcome this drawback, use of diisopropylethylamine (DIPEA) enabled to produce the expected dyes PP1 and PP2. The optical and electrochemical properties of the different dyes were examined. Theoretical calculations were also carried out to support the experimental results. To evidence the higher electron‐withdrawing ability of this electron acceptor, a comparison was established with two dyes (PP3 and PP4) comprising its shorter analogue.

Free Radical Photopolymerization and 3D Printing Using Newly Developed Dyes: Indane-1,3-Dione and 1H-Cyclopentanaphthalene-1,3-Dione Derivatives as Photoinitiators in Three-Component Systems

“…Noticeably, examples of dyes based on 1H-cyclopentanaphthalene-1,3-dione are extremely scarce in literature [42,[54][55][56][57], evidencing the interest and the novelty of the structures proposed in this work. Interestingly, their good light absorption properties @405 nm were anticipated by theoretical calculations and molecular design.…”

“…Here, E ox , E red , and E * (Es 1 ) are the oxidation potential of the electron donor (EDB), the reduction potential of the electron acceptor (Iod), the excited state energy level (calculated from the crossing point of UV-visible and fluorescence spectra), respectively. Similarly, the free energy change of triplet state ∆G et was calculated from Equations 3 and 4 [42] where the triplet state energy level is noted E * (E T1 ). Particularly, E * (E T1 ) was extracted from molecular energy level calculations (Gaussian 03 suite of programs).…”

“…Concerning the enhancement of the light absorption properties, the most straightforward route undoubtedly consists in developing dyes with a strong electronic delocalization resulting from the separation of the electron donor from the electron acceptors [40]. This strategy can be easily developed with push-pull dyes comprising an electron donor connected to an electron acceptor by mean of a π-conjugated or a nonconjugated spacer [41,42]. By improving the electron-donating ability of the electron releasing group or the electron-accepting ability of the electron withdrawing group, the position of the charge transfer band located in the visible region can be efficiently tuned.…”

Recent advances on push–pull organic dyes as visible light photoinitiators of polymerization

“…It has to be noticed that contrarily to the previous works where only the commercially available indane-1,3-dione was used, in the present case, 1H-cyclopentanaphthalene-1,3-dione EA1 and 2-(3-oxo-2,3-dihydro-1H-cyclopenta[b]naphthalen-1-ylidene)malononitrile EA2 had to be prepared starting from naphthalene-2,3-dicarboxylic acid [127,176]. By esterification of the diacid with ethanol, the Claisen reaction of diethyl naphthalene-2,3-dicarboxylate with ethyl acetate and sodium hydride could provide after hydrolysis EA1 in 91% yield for the two-steps.…”

“…3. Notably, malononitrile A1, [125] indanedione derivatives A2, [126,127] (thio)barbituric derivatives A3, [128] Meldrum derivatives A4, [129] pyridinium…”