By pursuing the strategy of manipulating natural compounds to obtain functional materials, in this work, we report on the synthesis and characterization of a luminescent cationic iridium complex (cis-1), designed starting from the catecholic neurotransmitter dopamine, exhibiting the unusual cis arrangement of the C∧N ligands. Through an integrated experimental and theoretical approach, it was possible to delineate the optoelectronic properties of cis-1. In detail, (a) a series of absorption maxima in the range 300−400 nm was assigned to metal-to-ligand charge transfer and weak and broad absorption maxima at longer wavelengths (400−500 nm) were ascribable to spin-forbidden transitions with a mixed character; (b) there was an intense red phosphorescence with emission set in the range 580−710 nm; and (c) a highest occupied molecular orbital was mainly localized on the metal and the 2-phenylpiridine ligand and a lowest unoccupied molecular orbital was localized on the N∧N ligand, with a ΔH−L set at 2.20 eV. This investigation allowed the design of light-emitting electrochemical cell (LEEC) devices endowed with good performance. The poor literature reporting on the use of cis-iridium(III) complexes in LEECs prompted us to investigate the role played by the selected cathode and the thickness of the emitting layer, as well as the doping effect exerted by ionic liquids on the performance of the devices. All the devices exhibited a deep red emission, in some cases, quite near the pure color (devices #1, #4, and #8), expanding the panorama of the iridium-based red-to-near-infrared LEEC devices. The characteristics of the devices, such as the brightness reaching values of 162 cd/m2 for device #7, suggested that the performances of cis-1 are comparable to those of trans isomers, opening new perspective toward designing a new set of luminescent materials for optoelectronic devices.
Valeria Criscuolo;Carmela T. Prontera;Michele Pavone;Orlando Crescenzi;Stefano Lettieri;Pasqualino Maddalena;Paola Manini
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