Abstract |
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-iPr(2)C(6)H(3) 9; C6H5 10), Ph2B[(NC8H5C(H)=N)(2)-1,4-C6H4]BPh2 11, Ph2B(NC16H9C(H)=N-Ar) (Ar = 2,6-iPr(2)C(6)H(3) 12; C6H5 13), and Ph2B[(NC16H9C(H)=N)(2)-1,4-C6H4]BPh2 14, 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 pi-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-iPr(2)C(6)H(3)N-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) |