Electrical properties of electrochemically doped organic semiconductors using light-emitting electrochemical cells

A counterion study of a series of [Cu(P^P)(N^N)][A] compounds with bis(phosphane) and 6-methyl and 6,6'-dimethyl-substituted 2,2'-bipyridine ligands for light-emitting electrochemical cells

The syntheses and characterisations of a series of heteroleptic copper(I) compounds [Cu(POP)(Mebpy)][A], [Cu(POP)(Me2bpy)][A], [Cu(xantphos)(Mebpy)][A] and [Cu(xantphos)(Me2bpy)][A] in which [A]- is [BF4]-, [PF6]-, [BPh4]- and [BArF4]- (Mebpy = 6-methyl-2,2'-bipyridine, Me2bpy = 6,6'-dimethyl-2,2'-bipyridine, POP = oxydi(2,1-phenylene)bis(diphenylphosphane), xantphos = (9,9-dimethyl-9H-xanthene-4,5-diyl)bis(diphenylphosphane), [BArF4]- = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate) are reported. Nine of the compounds have been characterised by single crystal X-ray crystallography, and the consequences of the different anions on the packing interactions in the solid state are discussed. The effects of the counterion on the photophysical properties of [Cu(POP)(N^N)][A] and [Cu(xantphos)(N^N)][A] (N^N = Mebpy and Me2bpy) have been investigated. In the solid-state emission spectra, the highest energy emission maxima are for [Cu(xantphos)(Mebpy)][BPh4] and [Cu(xantphos)(Me2bpy)][BPh4] (λemmax = 520 nm) whereas the lowest energy λemmax values occur for [Cu(POP)(Mebpy)][PF6] and [Cu(POP)(Mebpy)][BPh4] (565 nm and 563 nm, respectively). Photoluminescence quantum yields (PLQYs) are noticeably affected by the counterion; in the [Cu(xantphos)(Me2bpy)][A] series, solid-state PLQY values decrease from 62% for [PF6]-, to 44%, 35% and 27% for [BF4]-, [BPh4]- and [BArF4]-, respectively. This latter series of compounds was used as active electroluminescent materials on light-emitting electrochemical cells (LECs). The luminophores were mixed with ionic liquids (ILs) [EMIM][A] ([EMIM]+ = [1-ethyl-3-methylimidazolium]+) containing the same or different counterions than the copper(I) complex. LECs containing [Cu(xantphos)(Me2bpy)][BPh4] and [Cu(xantphos)(Me2bpy)][BArF4] failed to turn on under the LEC operating conditions, whereas those with the smaller [PF6]- or [BF4]- counterions had rapid turn-on times and exhibited maximum luminances of 173 and 137 cd m-2 and current efficiencies of 3.5 and 2.6 cd A-1, respectively, when the IL contained the same counterion as the luminophore. Mixing the counterions ([PF6]- and [BF4]-) of the active complex and the IL led to a reduction in all the figures of merit of the LECs.

Electrogenerated Chemiluminescence and Electroluminescence of N-Doped Graphene Quantum Dots Fabricated from an Electrochemical Exfoliation Process in Nitrogen-Containing Electrolytes

Artificial lighting sources are one of the most important technological developments for our modern lives; the search for cost-effective and efficient luminophores is therefore crucial to a sustainable future. Graphene quantum dots (GQDs) are carbon-based nanomaterials that exhibit exceptional optical and electronic properties, making them a prime candidate for a luminophore in a light-emitting device. Nitrogen-doped GQDs fabricated from a facile top-down electrochemical exfoliation process with a nitrogen-containing electrolyte in this report showed strong photoluminescent emission at 450 nm, and electrogenerated chemiluminescence at 660 nm in the presence of benzoyl peroxide as a coreactant. When introduced into solid-state light-emitting electrochemical cells, for the first time, the GQDs displayed a broad white emission centered at 610 nm, corresponding to Commision Internationale de l'eclairage (CIE) colour coordinates of (0.38, 0.36).