Syntheses and Photophysical Investigations of Cr(III) Hexadentate Iminopyridine Complexes and Their Tris(Bidentate) Analogues

Abstract

We report the preparation, photophysical characterization, and computed excited state energies for a family of Cr(III) complexes based on iminopyridine (impy) Schiff base ligands: compounds 1 and 2 feature hexadentate ligands where tren (tris-(2-aminoethyl)amine) caps three impy groups; compounds 3 and 4 are tris(bidentate) analogues of 1 and 2; compounds 2 and 4 contain methyl ester substituents to alter ligand donation properties relative to 1 and 3, respectively. Cyclic voltammograms exhibit multiple reversible ligand-based reductions; the hexadentate and tris(bidentate) analogues have almost identical reduction potentials, and the addition of ester substituents shifts reduction potentials by +200 mV. The absorption spectra of the hexadentate complexes show improved absorption of visible light compared to the tris(bidentate) analogues. Over periods of several hours to days, the complexes undergo ligand-substitution-based decomposition in 1 M HCl((aq)) and acetonitrile. For freshly prepared sample solutions in CH(3)CN, time-resolved emission and transient absorption measurements for 4 show a doublet excited state with 17-19 μs lifetime at room temperature, while no emission or transient absorption signals from the doublet states are observed for the hexadentate analogue 2 under the same conditions. The electronic structure contributions to the differences in observed photophysical properties are compared by extensive computational analyses (UB3LYP MD-DFT and TD-DFT-NTO). These studies indicate that the presence of nonligated bridgehead nitrogen atoms for 1 and 2 significantly reduce excited state doublet, quartet, and sextet energies and change the character of the low lying doublet states in comparison to species that show population of doublet excited states.

CrIIIas an alternative to RuIIin metallo-supramolecular chemistry

“…This transforms the modelling of the E( 2 T 1 ) − E( 2 E) energy gap, for which Jorgensen's approach predicts 66B 2 /Δ (eqn (5)), to only 26B 2 /Δ (eqn (6)). Compared with the theoretical set of exact energies computed by Ferguson by means of full Eisenstein's matrices with B = 680 cm −1 and C = 2720 cm −1 (C/ B = 4.0), 116,117 the exact computed E( 2 T 1 ) − E( 2 E) energy gap amounts to 630 cm −1 for Δ = 19 940 cm −1 in fair to good agreement with the prediction of the second-order correction 26B 2 / Δ = 603 cm −1 (eqn (6)), but rather far from 1531 cm −1 obtained with eqn (5). We conclude that only a complete ligand-field treatment is capable of extracting reliable Racah parameters B and C for Cr III complexes, 119 but eqn (6) seems superior to eqn (5) when a rough modeling of the energy of the lowest spinflip 2 E excited state is foreseen.…”

“…The additional consideration of configuration interaction between the states of the same multiplicity and symmetry, but from different strong field configurations led Jorgensen 59 to introduce second-order corrections αB 2 /Δ in eqn (3)- (5), which are derived from the off-diagonal elements of the Tanabe-Sugano matrices.…”

Synthesis and characterisation of two new tripodal metalloligands incorporating zinc(II)

“…The appropriate isotope patterns for their charged states of 1 and 2 ( Fig. S6 and S8) were observed, thus indicating the presence of [1-ClO 4 -] ? and [2-ClO 4 -] ?…”

“…For example, condensation of 2-pyridinecarboxaldehyde with tren in a 3:1 ratio yields the corresponding tris-imine derivative, tris-2-(2-pyridylimine ethyl)amine, whose metal ion coordinating ability has been well documented [3][4][5][6][7][8][9][10][11][12][13][14].…”

Luminescence and Light‐Driven Energy and Electron Transfer from an Exceptionally Long‐Lived Excited State of a Non‐Innocent Chromium(III) Complex

“…Chromium(III) cage complexes with five-membered chelate rings show shorter luminescence lifetimes and lower quantum yields. [19] Deuteration of the ddpd ligand boosts the key luminescence data of [Cr-(ddpd) 2 ] 3+ to F = 30.0 %and t = 2300 msindeaerated CD 3 CN (Table 1). [20] These favorable photophysical data of [Cr-(ddpd) 2 ] 3+ enable its application in temperature,p ressure and dioxygen sensing,a sw ell as in photocatalysis and photodynamic therapy.…”