Violet-blue emitting 2-(N-alkylimino)pyrrolyl organoboranes: Synthesis, structure and luminescent properties

• Published in: Dyes and pigments 2017-05, Vol.140, p.520-532
• Main Authors: Krishnamoorthy, Paramasivam, Ferreira, Bruno, Gomes, Clara S.B., Vila-Viçosa, Diogo, Charas, Ana, Morgado, Jorge, Calhorda, Maria José, Maçanita, António L., Gomes, Pedro T.
• Format: Article
• Language: English
• Subjects: Boron; DFT; Fluorescence; Iminopyrrolyl ligands; OLED
• ISSN: 0143-7208; 1873-3743
• DOI: 10.1016/j.dyepig.2016.11.017

The condensation reactions of 2-formylpyrrole (1) or 2-formylphenanthro[9,10-c]pyrrole (2) with various aliphatic amines afforded the corresponding 2-iminopyrrole ligand precursors 3–10, which, upon stoichiometric reaction with BPh3, led to the new mononuclear boron chelate compounds Ph2B[NC4H3C(H)N-R] (R = Me 11; iPr 12; tBu 13; nOct 14; Cy 15; Adam 16), and Ph2B(NC16H9C(H)N-R) (R = Me 17; Adam 18), respectively. Boron complexes 11–16, containing a simple 2-(N-alkylformimino)pyrrolyl ligand, are violet emitters and showed relatively modest fluorescence quantum efficiencies in solution (10%–16%), whereas complexes 17 and 18, bearing the π-extended 2-(N-alkylformimino)phenanthro[9,10-c]pyrrolyl ligand, are blue emitters presenting enhanced quantum efficiencies of 35% and 43%, respectively, in THF solution. DFT and TDDFT calculations were in good agreement with experimental results, showing that π systems (pyrrolyl and phenanthropyrrolyl in this case) have a strong influence on the observed optical properties by changing the nature of the low energy transitions. Non-doped single-layer light-emitting diodes (OLEDs) were fabricated with complexes 11–18, deposited essentially by spin coating, those of complexes 17 and 18 revealing maximum luminances of 69 and 88 cd m−2, respectively. Violet-blue emitting 2-(N-Alkylimino)pyrrolyl organoboranes are synthesized, their structure and luminescent properties being described. [Display omitted] •Several 2-(N-alkylimino)pyrrolyl diphenyl boron complexes were synthesized.•Fluorescence properties of these blue-violet emitting compounds were studied.•Non-radiative decays are much weaker than those of the N-2,6-R2-arylimino analogues.•DFT and TDDFT calculations support the experimental results.•Simple OLED devices reveal maximum luminances of ca. 90 cd m−2.