Highly red-emissive salen–indium complexes: impact of 4-amino-substitution on the photophysical properties

Abstract

4-NR2-appended salen–indium complexes were prepared via a one-pot synthetic pathway. The complexes exhibited narrow-bandwidth red emissions with high photoluminescence quantum yields that are the highest among the reported salen-based luminophores.

Effect of bridging units on the photophysical properties of 4‐NEt2‐appended salen−indium complexes

“…Thus, the low‐energy electronic transition in 1 – 3 can be assigned to the ππ * transition process centered on the entire salen moieties with a partial ICT character between the 4‐NEt 2 ‐appended phenoxy parts and the bridged imine moieties. Indeed, this finding is similar to those observed in typical salen‐based indium complexes 23–28 . The calculated low‐energy absorption wavelengths ( λ calc , Figure 4 and Table 2) were in the order of 1 (362 nm) < 2 (430 nm) < 3 (456 nm) in toluene, which was consistent with that of the experimentally observed low‐energy absorption maxima ( λ abs , Table 1).…”

“…Complex 1 possessed a square‐pyramidal geometry around the indium center, as estimated by the trigonality parameter ( τ ) 38 value of 0.03, indicating a nearly coplanar salen framework around the indium center. This feature is also similar to the molecular structure of 4 23 except for π ‐conjugation in the entire salen ligand (See the DFT results described under the Section Computational Study).…”

“…All spectrophotometric grade solvents (acetonitrile [MeCN], methanol [MeOH], and toluene) and commercially available reagents (4‐(diethylamino)salicylaldehyde, ethylenediamine, 3,4‐diaminobenzonitrile, diaminomaleonitrile, and o ‐phenylenediamine) were used without further purification. Trimethylindium (InMe 3 ) was prepared according to the procedures reported in previous studies 23–30 . Deuterated chloroform (CDCl 3 ) was obtained from Cambridge Isotope Laboratories and used after drying by activated molecular sieves (5 Å).…”

“…From the viewpoint of these explorations, our group has developed different group 13‐based salen complexes 19–22 . In particular, recent studies have mainly focused on the salen‐based indium complexes that exhibit multicolor emission features and high quantum efficiencies 23–28 . This feature can be achieved by controlling the electronic effect of either diimine parts or phenoxy groups.…”

“…Therefore, to overcome this, we recently developed a series of C4‐appended (4‐NR 2 ) salen−In complexes containing a diaminonitrile (EtCN 2 ) bridge with a strong electron‐withdrawing ability (Figure 1b). 23 These complexes exhibited highly efficient red emissions and excellent color purity due to the efficient interaction between the 4‐NR 2 donor and the EtCN 2 acceptor.…”