Data di Pubblicazione:
2022
Citazione:
NEW NCN-PLATINUM(II) COMPLEXES WITH LUMINESCENT PROPERTIES / F. Fagnani ; tutor: C. Dragonetti ; co-tutor: A. Colombo ; coordinatore: D. Passarella. Dipartimento di Chimica, 2022 Oct 05. 35. ciclo, Anno Accademico 2022.
Abstract:
During the doctoral period, my research has been focused on the synthesis and characterization of novel NCN-based platinum(II) complexes, obtaining more than twenty completely new compounds.
These complexes have a terdentate chelating ligand with the general scaffold of a 1,3-di(2-pyridyl)benzene and were designed following different strategies:
i) Complexes PtCl1-PtCl7 have unsubstituted pyridines and different groups in position 5 of the benzene ring, i.e. a mesityl, a triphenylamine, a pyrenyl, a phenyl-carbazole, a carbazole, a 2-thienyl and a methyl.
The synthesis of the NCN ligands started from some dibromo intermediates, obtained in different ways: from a Suzuki-Miyaura coupling of 1,3,5-tribromobenzene with the suitable aryl-boronic acid in the case of L1-L4; from 1,3-dibromo-5-fluorobenzene reacting with carbazole for L5; from a Stille coupling of tribromobenzene and 2-SnBu3-thiophene for L6.
Once obtained the dibromo intermediates, the Stille coupling of them (and of 1,3-dibromotoluene for L7) with 2-SnBu3-pyridine provided the terdentate ligands. Finally, the complexation step with K2PtCl4 in glacial AcOH leads to complexes PtCl1-PtCl7.
ii) The second group of new complexes is composed of fifteen derivatives of the NCN-PtCl compounds PtCl1-PtCl2 and PtCl6-PtCl7, by replacement of the chloride ligand with six anionic species.
These ancillary ligands are two aromatic thiolates, a simple azide, a phthalimide, a thioacetate and an isothiocyanate.
The substitution reactions were carried out in acetone or MeOH, at room temperature and under Argon atmosphere, using a large excess of the new ligand.
iii) Finally, PtCl8-PtCl13 still have the same -Cl ancillary ligand and substituents on the benzene ring (mesityl, 4-NPh2-phenyl, 2-thienyl, methyl) of some previously reported compounds, but new groups (i.e. 4-hexyl-2-thienyl, 4-NPh2-phenyl) have been added to the pyridines, to test the effect of an expanded aromatic system.
These complexes are a development of some compounds of the first group, not having substituents on the pyridines. The synthesis started from the two different 4-aryl-2-chloropyridines (having a hexyl-thienyl or a triphenylamino moiety in para position), whose substituents were introduced by Suzuki-Miyaura coupling. Then, they reacted in a further Suzuki-Miyaura coupling with boronic diesters obtained from the already discussed dibromo intermediates. Finally, the typical complexation reaction was carried out in the presence of K2PtCl4.
For all complexes reported before, the UV-Vis absorption spectra in CH2Cl2 were registered at different concentrations, in order to calculate the molar extinction coefficients (ε). Moreover, most of the complexes were studied from the luminescence point of view, using dearated dichloromethane solutions; in that way, the excitation and emission spectra, together with the absolute Quantum Yields and the Lifetimes, were obtained. The Freeze-Pump-Thaw procedure, used to remove oxygen from the solution, was necessary since the long-living triplet states of the complexes are very efficiently quenched by the fundamental triplet state of O2.
Concerning the Quantum Yields, very high values were achieved in the case of complexes Pt1 (90%), Pt3 (87%), Pt8 (83%), Pt9 (89%) and Pt10 (79%), so the substitution of the -Cl is very often useful to improve the photophysical properties.
Moreover, a remarkable increase of the QY is brought about also by the expansion of the aromatic system via new moieties on the pyridines. In fact, the values pass from 62% (PtCl1) to 96% (PtCl8) and 89% (PtCl12), and from 54% (PtCl6) to 100% (PtCl10).
Complex Pt1, being very interesting because of its luminescence properties, was used for the preparation of three OLED
Tipologia IRIS:
Tesi di dottorato
Elenco autori:
F. Fagnani
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