<strong>Synthesis and characterization of novel thienyl-phthalazine based heterocyclic systems functionalized with (bi)thiophene moieties</strong>

Abstract

The phthalazine heterocycle has a highly π-deficient aromatic character that makes it a good candidate to be incorporated as electron acceptor group, or even as spacer with auxiliary electron withdrawing abilities, into push-pull systems. Additionally, offers the possibility of protonation, hydrogen bond formation, and chelation through the nitrogen atoms.1  Phthalazine derivatives have applications as therapeutic agents,2 chemiluminescent materials,3 ligands in transition metal catalysis,4 and as optical materials.5 Some time ago, our research group developed a methodology for the preparation of phthalazine derivatives in three steps, affording halo-thienyl-phthalazine derivatives that play an important role in diazine chemistry since they offer great potential for further functionalization by nucleophilic displacement of the halogen, making numerous otherwise inaccessible diazines become available.6 In continuation of the work developed before by our research group,4b-c, 6 we report in this communication the synthesis and the evaluation of the optical properties of two novel thienyl-phthalazine derivatives, functionalized with (bi)thiophene moieties, having in mind further functionalization in order to prepare push-pull heterocyclic systems for several optical and photovoltaic applications. These studies showed that the optical properties could be readily tuned by varying the π-conjugation path length through the introduction of a second thiophene unit.   Acknowledgements: Thank are due to Fundação para a Ciência e Tecnologia (Portugal) and FEDER-COMPETE for financial support through Centro de Química (UID/QUI/00686/2013 and UID/ QUI/0686/2016), and a PhD grant to S. S. M. Fernandes (SFRH/BD/87786/2012). The NMR spectrometer Bruker Avance III 400 is part of the National NMR Network and was purchased with funds from FCT and FEDER.   References Achelle, S.; Plé, N.; Turck, A., Incorporation of pyridazine rings in the structure of functionalized π-conjugated materials. RSC Adv. 2011, 1 (3), 364-388. Vila, N.; Besada, P.; Costas, T.; Costas-Lago, M. C.; Terán, C., Phthalazin-1(2H)-one as a remarkable scaffold in drug discovery. Eur. J. Med. Chem. 2015, 97, 462-482. (a) Achelle, S.; Baudequin, C.; Plé, N., Luminescent materials incorporating pyrazine or quinoxaline moieties. Dyes Pigments 2013, 98 (3), 575-600; (b) Yoshida, H.; Ureshino, K.; Ishida, J.; Nohta, H.; Yamaguchi, M., Chemiluminescent properties of some luminol related compounds (II). Dyes Pigments 1999, 41 (3), 177-182; (c) Achelle, S.; Rodríguez-López, J.; Katan, C.; Robin-le Guen, F., Luminescence behavior of protonated methoxy-substituted diazine derivatives: toward white light emission. J. Phys. Chem. C 2016, 120 (47), 26986-26995. (a) Kolb, H. C.; VanNieuwenhze, M. S.; Sharpless, K. B., Catalytic asymmetric dihydroxylation. Chem. Rev. 1994, 94 (8), 2483-2547; (b) Figueiredo, H.; Silva, B.; Raposo, M. M. M.; Fonseca, A. M.; Neves, I. C.; Quintelas, C.; Tavares, T., Immobilization of Fe(III) complexes of pyridazine derivatives prepared from biosorbents supported on zeolites. Microporous Mesoporous Mater. 2008, 109 (1–3), 163-171; (c) Figueiredo, H.; Silva, B.; Quintelas, C.; Raposo, M. M. M.; Parpot, P.; Fonseca, A. M.; Lewandowska, A. E.; Bañares, M. A.; Neves, I. C.; Tavares, T., Immobilization of chromium complexes in zeolite Y obtained from biosorbents: Synthesis, characterization and catalytic behaviour. Appl. Catal., B: Environ. 2010, 94 (1–2), 1-7. (a) Cheng, Y.; Ma, B.; Wudl, F., Synthesis and optical properties of a series of pyrrolopyridazine derivatives: deep blue organic luminophors for electroluminescent devices. J. Mater. Chem. 1999, 9 (9), 2183-2188; (b) Achelle, S.; Rodríguez-López, J.; Bureš, F.; Robin-le Guen, F., Dipicolylamine styryldiazine derivatives: Synthesis and photophysical studies. Dyes Pigments 2015, 121, 305-311; (c) Cvejn, D.; Achelle, S.; Pytela, O.; Malval, J.-P.; Spangenberg, A.; Cabon, N.; Bureš, F.; Robin-le Guen, F., Tripodal molecules with triphenylamine core, diazine peripheral groups and extended p-conjugated linkers. Dyes Pigments 2016, 124, 101-109. Raposo, M. M. M.; Sampaio, A. M. B. A.; Kirsch, G., A convenient access to thienyl-substituted phthalazines. J. Heterocycl. Chem. 2005, 42 (7), 1245-1251.