Fluorosolvatochromism and hyperpolarizability of one-arm and two-arms nitro-compounds bearing heterocyclic rings

• Published in: Journal of photochemistry and photobiology. A, Chemistry. Vol. 368; pp. 190 - 199
• Main Authors: Carlotti, B., Cesaretti, A., Cacioppa, G., Elisei, F., Odak, I., Škorić, I., Spalletti, A.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 01.01.2019; Elsevier BV
• Subjects: Charge transfer; Fluorosolvatochromism; Hyperpolarizability coefficient; Isomers; Molecular structure; Nitro-derivatives; NLO materials; Optics; Organic materials; Push-pull heterocyclic compounds; Pyridines; Quantum dots; Quantum mechanics; Nitro-derivatives; Fluorosolvatochromism; Hyperpolarizability coefficient; Push-pull heterocyclic compounds; NLO materials
• ISSN: 1010-6030; 1873-2666
• DOI: 10.1016/j.jphotochem.2018.09.043

Strong fluorosolvatochromism exhibited by compounds with Acceptor-π-Het and Acceptor-π-Het-π-Acceptor structures in agreement with the substantial photoinduced intramolecular charge transfer (from the heteroaromatics to the nitro groups) allowed hyperpolarizability coefficients of significant value to be estimated through the solvatochromic method (βCT up to 1030 × 10−30 esu-1 cm5, larger for the thiophen-derivatives and for the two-arms compounds). [Display omitted] •Synthesis and spectral behaviour of mono- and two-branched nitro-derivatives bearing pyridine, furan or thiophene rings.•Strong fluorosolvatochromism and photoinduced ICT, from the heteroaromatics to the nitro groups, undisclosed by DFT calculations.•High hyperpolarizability coefficient βCT estimated through a solvatochromic method.•The new Acceptor-π-Core π-Acceptor structural motif of interest for new efficient NLO materials. We report here the spectral characterization and hyperpolazizatin coefficinet of all-trans isomers of two-branched push-pull systems of interest as new efficient organic materials for Non Linear Optics, compared with the corresponding mono-branched analogues. These molecules are characterized by Acceptor-π-Het-π-Acceptor and Acceptor-π-Het structures, respectively, where the strong electron acceptor is the nitro group and the electron rich portion is a heteroaromatic ring (pyridine, furan and thiophene). These compounds exhibit strong fluorosolvatochromism, in agreement with the substantial photoinduced intramolecular charge transfer (from the heteroaromatics to the nitro groups) undisclosed by quantum mechanical calculations. The hyperpolarizability of these molecules, here estimated by the solvatochromic method, reaches significant values in all cases: enhanced for the two-branched systems with respect to their mono-branched analogues and higher for the furan/thiophene derivatives with respect to the pyridine ones. Surprisingly, hyperpolarizabilities of the symmetrical Acceptor-π-Het-π-Acceptor structures are found to be similar or higher than those of the asymmetrical Acceptor-π-Het-π-Donor counterparts.