Patrícia S. Lopes

Boron complexes of aromatic ring fused iminopyrrolyl ligands: synthesis, structure, and luminescence properties

The condensation reactions of 2-formylindole (1) or 2-formylphenanthro[9,10-c]pyrrole (2) with various aromatic amines afforded the corresponding phenyl or phenanthrene ring fused mono-/bis-iminopyrrole ligand precursors 3-8, which, upon reaction with BPh3 in an appropriate molar ratio, led to the new mono- and diboron chelate compounds Ph2B[NC8H5C(H)[double bond, length as m-dash]N-2,6-Ar] (Ar = 2,6-iPr2C6H39; C6H510), Ph2B[(NC8H5C(H)[double bond, length as m-dash]N)2-1,4-C6H4]BPh211, Ph2B(NC16H9C(H)[double bond, length as m-dash]N-Ar) (Ar = 2,6-iPr2C6H312; C6H513), and Ph2B[(NC16H9C(H)[double bond, length as m-dash]N)2-1,4-C6H4]BPh214, respectively. Boron complexes 12-14, containing a phenanthrene fragment fused to the pyrrolyl C3-C4 bond, are highly fluorescent in solution, with quantum efficiencies of 37%, 61% and 58% (in THF), respectively, their emission colours ranging from blue to orange depending on the extension of π-conjugation. Complexes 9-11, containing a benzene fragment fused to the pyrrolyl C4-C5 bond, are much weaker emitters, exhibiting quantum efficiencies of 10%, 7% and 6%, respectively. DFT and TDDFT calculations showed that 2,6-iPr2C6H3N-substituents or, to a smaller extent, the indolyl group prevent a planar geometry of the ligand in the excited state and reveal the existence of a low energy weak band in all the indolyl complexes, which is responsible for the different optical properties. Non-doped single-layer light-emitting diodes (OLEDs) were fabricated with complexes 9-14, deposited by spin coating, that of complex 13 revealing a maximum luminance of 198 cd m-2.

Exploring the influence of steric hindrance and electronic nature of substituents in the supramolecular arrangements of 5-(substituted phenyl)-2-formylpyrroles

A family of 5-(substituted phenyl)-2-formylpyrrole compounds, exhibiting different electronic and steric features at the phenyl ring, was synthesised through the formylation reaction of the corresponding 2-(substituted phenyl)pyrrole precursors, using Vilsmeier–Haack acylation conditions. The products were obtained in moderate to high yields, being systematically characterised by NMR spectroscopy, elemental analysis and single crystal X-ray diffraction. The corresponding crystalline packings were discussed on the basis of three types of arrangements, leading to the formation of dimers, polymers or the newly observed tetramers, all of them essentially governed by strong N–H⋯O hydrogen bonding interactions. Important C–H⋯O, C–H⋯π, π⋯π and, in the case of fluorinated compounds, C–H⋯F interactions also contributed to the growth of the three-dimensional crystalline network. DFT calculations helped to rationalise the relationship between the steric and electronic properties of the molecules and the basic units observed in the corresponding solid state structures.

Iminopyrrole derivatives containing electron-withdrawing substituents: the formation of dimers and supramolecular arrangements

The crystal structures of two p-substituted phenylformiminopyrrole derivatives, namely 2-[(4-fluorophenyl)iminomethyl]pyrrole, C(11)H(9)FN(2), (1), and 2-[(1H-pyrrol-2-ylmethylidene)amino]benzonitrile, C(12)H(9)N(3), (2), bear F and C[triple-bond]N electron-withdrawing groups, respectively. Both structures feature two independent molecules in the asymmetric unit forming dimers via N-H...N hydrogen bonds. In the case of (1), each dimer interacts with two other dimers via C-H...F contacts, thus forming one-dimensional chains in the b direction, whereas in the case of (2), a weak C-H...N interaction connects the dimers in one-dimensional chains in the (110) direction.