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

2016; Royal Society of Chemistry; Volume: 45; Issue: 39 Linguagem: Inglês

10.1039/c6dt02771g

1477-9234

D. Suresh, Bruno Ferreira, Patrícia S. Lopes, Clara S. B. Gomes, P. Krishnamoorthy, Ana Charas, Diogo Vila‐Viçosa, Jorge Morgado, Maria José Calhorda, António L. Maçanita, Pedro T. Gomes,

Organoboron and organosilicon chemistry

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.