Tuning Photophysical Properties by p-Functional Groups in Zn(II) and Cd(II) Complexes with Piperonylic Acid |
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| Authors: | Francisco Snchez-Frez Joaquim Mª Rius-Bartra Jos A Aylln Teresa Calvet Merc Font-Bardia Josefina Pons |
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| Institution: | 1.Departament de Química, Universitat Autònoma de Barcelona, 08193 Barcelona, Spain; (F.S.-F.); (J.M.R.-B.); (J.A.A.);2.Departament de Mineralogia, Petrologia i Geologia Aplicada, Universitat de Barcelona, Martí i Franquès s/n, 08028 Barcelona, Spain;3.Unitat de Difracció de Raig-X, Centres Científics i Tecnològics de la Universitat de Barcelona (CCiTUB), Universitat de Barcelona, Solé i Sabarís, 1-3, 08028 Barcelona, Spain; |
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| Abstract: | Aggregation between discrete molecules is an essential factor to prevent aggregation-caused quenching (ACQ). Indeed, functional groups capable of generating strong hydrogen bonds are likely to assemble and cause ACQ and photoinduced electron transfer processes. Thus, it is possible to compare absorption and emission properties by incorporating two ligands with a different bias toward intra- and intermolecular interactions that can induce a specific structural arrangement. In parallel, the π electron-donor or electron-withdrawing character of the functional groups could modify the Highest Ocuppied Molecular Orbital (HOMO)–Lowest Unocuppied Molecular Orbital (LUMO) energy gap. Reactions of M(OAc)2·2H2O (M = Zn(II) and Cd(II); OAc = acetate) with 1,3-benzodioxole-5-carboxylic acid (Piperonylic acid, HPip) and 4-acetylpyridine (4-Acpy) or isonicotinamide (Isn) resulted in the formation of four complexes. The elucidation of their crystal structure showed the formation of one paddle-wheel Zn(μ-Pip)2(4-Acpy)]2 (1); a mixture of one dimer and two monomers Zn(µ-Pip)(Pip)(Isn)2]2·2Zn(Pip)2(HPip)(Isn)]·2MeOH (2); and two dimers Cd(μ-Pip)(Pip)(4-Acpy)2]2 (3) and Cd(μ-Pip)(Pip)(Isn)2]2·MeOH (4). They exhibit bridged (1, µ2-η1:η1), bridged, chelated and monodentated (2, µ2-η1:η1, µ1-η1:η1 and µ1-η1), or simultaneously bridged and chelated (3 and 4, µ2-η2:η1) coordination modes. Zn(II) centers accommodate coordination numbers 5 and 6, whereas Cd(II) presents coordination number 7. We have related their photophysical properties and fluorescence quantum yields with their geometric variations and interactions supported by TD-DFT calculations. |
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| Keywords: | Zn(II) and Cd(II) 4-acetylpyridine isonicotinamide piperonylic acid photoluminescence |
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