Copper(i) complexes for sustainable light-emitting electrochemical cells

Origin of a counterintuitive yellow light-emitting electrochemical cell based on a blue-emitting heteroleptic copper(i) complex

“…6). Although a LC character is unusual for [Cu(N^N)(P^P)] + , in which the metal-charge transfer nature is classically observed, 2,11,12,14,17,18,[20][21][22][23][24] it is consistent with the structured shape of both PL and EL responses. Even if at the GS geometry, there are several triplet states (T 1 -T 3 ) lying between the optically populated S 1 and the ground state, at the structurally optimized S 1 and T 1 geometries, S 1 is separated from the ground state only by T 1 (Fig.…”

“…Indeed, a shift of around 70-100 nm between PL and EL responses represents one of the largest reported in LECs to date. 9,[13][14][15][22][23][24] In general, the EL red-shifts around 20 nm compared to the PL due to the energy stabilization of the excited state under external electrical stimuli. 9,10,15 In the few cases, in which a large shift has been reported, this has been rationalized in terms of (i) a change in the nature of the lowest emitting state due to the concentration effect of the films, 54 and (ii) a reversible substitution of the ligands due to the weak coordination to the Cu(I), 12 and (iii) a change in the distribution of excited states due to the polarization effects.…”

“…Even if at the GS geometry, there are several triplet states (T 1 -T 3 ) lying between the optically populated S 1 and the ground state, at the structurally optimized S 1 and T 1 geometries, S 1 is separated from the ground state only by T 1 (Fig. 6) 2,11,12,14,17,18,[20][21][22][23][24] In detail, the minimum of the potential energy surface of 1 in the S 1 excited state is located 0.44 eV above the energy of the system at the T 1 optimized geometry, leading to a ΔE S 1 -T 1 > 3000 cm −1 . This points to a lack of TADF that can be easily explained by the LC nature of the excited state that provides a large exchange integral between both excited states, as suggested by the large ΔE S 1 -T 1 .…”

“…9,10,15 As prime examples in [Cu(N^N)(P^P)] + LECs, the efficiency and the stability have been enhanced by designing N^N ligands with substituents strategically attached to shield the coordination sphere and/or increasing the planarity of the ligands. 9,[13][14][15][16][22][23][24] These recent achievements pinpoint the great potential of copper(I) complexes to replace complexes based on the much more rare and expensive iridium(III) in the near future. In this context, the quest for blue LECs based on copper(I) complexes is at the forefront of the field.…”

Luminescent Ionic Transition‐Metal Complexes for Light‐Emitting Electrochemical Cells

“…[148][149][150][151][152][153][154][155] Herein, only the most significant reports from early times will be summarized. More generally, we will illustrate the latest advances obtained in iTMCs-LECs in terms of turn-on time, stability, efficiency, and color.…”