The impressive progress in organic light-emitting diodes (LEDs) has been highly driven by the synthesis of new materials. In particular, boron-based complexes have been investigated for LEDs, combining high photoluminescence (PL) efficiency and good electron-transport properties. Several studies have shown that the extension of these complexes to combine multi-boron centers may improve the materials properties [1,2].
We have been investigating a particular series of mono- and di-boron complexes incorporating iminopyrrolyl ligands (see Figure 1). A wide range of complexes was synthesized and characterized. CW and picosecond time-resolved photoluminescence studies were carried out to assess the effect of the molecular structure on their properties. LEDs were prepared by spin coating inside a glove box and characterized. We find that some of such complexes exhibit high performances in single-layer structures, evidencing ambipolar charge transport.
Acknowledgments - The authors thank Fundação para a Ciência e Tecnologia, Portugal, for financial support (Projects PTDC/QUI/65474/2006, PEst-OE/QUI/UI0100/2011-2012, and PEst-OE/EEI/LA0008/2011) and for fellowships to D.S. and C.S.B.G. (SFRH/BPD/47853/2008 and SFRH/BPD/64423/2009, respectively).

[1] Z. Zhang, H. Bi, Y. Zhang, D. Yao, H. Gao, Y. Fan, H. Zhang, Y. Wang, Y. Wang, Z. Chen, D. Ma, Inorganic Chemistry, Vol. 48, page 7230, 2009.
[2] C. Sun, Z. M. Hudson, M. G. Helander, Z.-H. Lu, S. Wang, Organometallics, Vol. 30, page 5552, 2011.