New thienylpyrrolyl-cyanoacetic acid derivatives: synthesis and evaluation of the optical and solvatochromic properties

Among the organic molecules, the so called push-pull or dipolar molecules (D-π-A) offer versatility of synthesis and ability to modulate their photophysical and photochemical properties.

The cyanoacetic acid moiety has been used extensively as the acceptor group in D-π-A molecules motivated by its easy/inexpensive synthesis and ability to simultaneously act as a strong electron withdrawing moiety, as well as a stable anchoring group in dye-sensitized solar cells (DSSCs).^[1]

Our previous work on the synthesis and characterization of D-π-A chromophores in which the donor part (D) is represented by a p-excessive five-membered heteroaromatic system (pyrrole or thiophene) functionalized by electron donor groups and the acceptor part (A) is a strong electron acceptor group (“classical” or an electron-deficient heterocycle) has shown that they exhibit excellent solvatochromic, photochromic, emissive properties, good photovoltaic efficiencies, exceptional thermal stabilities and good to excellent NLO responses.^[2]

In this work, we report the synthesis of new D-π-A chromophores functionalized with cyanoacetic acid as acceptor group, linked to the thienylpyrrole heterocyclic system, which plays the dual role of π-bridge and auxiliary donor group. Thienylpyrrolyl-cyanoacetic acid derivatives were obtained in excellent yields through a simple Knoevenagel condensation of the corresponding precursor aldehydes with cyanoacetic acid in acetonitrile at reflux, using piperidine as catalyst, and the optical and solvatochromic properties of the novel push-pull systems were evaluated.

References:

1. (a) Park, K.-W.; Serrano, L. A.; Ahn, S.; Baek, M. H.; Wiles, A. A.; Cooke, G.; Hong, J. Tetrahedron 2017, 73 (8), 1098-1104; (b) Ortega, E.; Montecinos, R.; Cattin, L.; Díaz, F. R.; del Valle, M. A.; Bernède, J. C. J. Mol. Struct. 2017, 1141, 615-623; (c) Zhang, L.; Cole, J. M. ACS Appl. Mater. Interfaces 2015, 7 (6), 3427-3455.
2. (a) Fernandes, S. S. M.; Castro, M. C. R.; Mesquita, I.; Andrade, L.; Mendes, A.; Raposo, M. M. M. Dyes Pigments 2017, 136, 46-53; (b) Fernandes, S. S. M.; Mesquita, I.; Andrade, L.; Mendes, A.; Justino, L. L. G.; Burrows, H. D.; Raposo, M. M. M. Org. Electron. 2017, 49, 194-205; (c) Garcia-Amorós, J.; Castro, M. C. R.; Coelho, P.; Raposo, M. M. M.; Velasco, D. Chem. Comm. 2016, 52 (29), 5132-5135; (d) Castro, M. C. R.; Belsley, M.; Raposo, M. M. M. Dyes Pigments 2016, 131, 333-339; (e) Pina, J.; Seixas de Melo, J. S.; Batista, R. M. F.; Costa, S. P. G.; Raposo, M. M. M. J. Org. Chem. 2013, 78 (22), 11389-11395; (f) Coelho, P. J.; Castro, M. C. R.; Fernandes, S. S. M.; Fonseca, A. M. C.; Raposo, M. M. M. Tetrahedron Lett. 2012, 53 (34), 4502-4506; (g) Pina, J.; de Melo, J. S. S.; Batista, R. M. F.; Costa, S. P. G.; Raposo, M. M. M. Phys. Chem. Chem. Phys. 2010, 12 (33), 9719-9725; (h) Batista, R. M. F.; Costa, S. P. G.; Malheiro, E. L.; Belsley, M.; Raposo, M. M. M. Tetrahedron 2007, 63 (20), 4258-4265.

Acknowledgements

Thanks are due to Fundação para a Ciência e Tecnologia (Portugal) for financial support through project PEst-C/QUI/UI0686/2011 (F-COMP-01-0124-FEDER-022716), FEDER-COMPETE and a post-doctoral grant to R.M.F. Batista (SFRH/BPD/79333/2011). The NMR spectrometer Bruker Avance III 400 is part of the National NMR Network, and was purchased with funds from POCI2010 (FEDER) and FCT.