Photoracemization and excited state relaxation through non-adiabatic pathways in chromium (III) oxalate ions

Abstract

Computational studies on the photochemistry of the open-shell chromium oxalate [Cr(C(2)O(4))(3)](3-) ion, including its non-adiabatic relaxation pathways, have been performed. The presence of the peaked conical intersection of a quasi-Jahn-Teller type, connecting the (4)T state with (4)A(2) ground state, accounts for the observed photoinduced racemization. This involves the rupture of one of the Cr-O bonds and the complex forms an unstable trigonal bipyramid form that connects both ground state stereoisomers with the excited quartet manifold. Intersystem crossing seams have been located between the (4)T and lower lying (2)E state which can quench the quartet reaction and lead to (2)E → (4)A(2) emission.

Ultrafast photo-induced ligand solvolysis of cis-[Ru(bipyridine)2(nicotinamide)2]2+: experimental and theoretical insight into its photoactivation mechanism

“…Note that, isomerisation as a result of excited state PCI relaxation has been reported previously for other metal complexes. 58,59 Here though, we only observe experimental evidence for the formation of the cis isomer of 2, suggesting that the pro-trans-PCI structure is never accessed. Unlike the pro-cis-PCI, the pro-trans-PCI clearly exhibits much greater deviation from a true SP geometry due to steric distortion of the two bpy ligands induced by the adjacent NA (see structures in Fig.…”

Reversible Breathing Process and Associated Thermochromism of a Stacked-Layer Porous Supramolecular Material

“…I exhibits three broad and one narrow peaks. The first peak occurring in the UV domain around 233.3 nm (broad band) is typical of the ligand–metal charge transfer (LMCT) from the oxalate to the chromium ion and the intraligand π → π* transitions of the aromatic amp ring occurring in the shoulder of this broad peak at around 270 nm. − The three remaining peaks occur around 433.3 nm (broad band), 560 nm (broad band) and 694.5 nm (narrow band). They represent, respectively, the chromium­(III) octahedra transitions: 4 A 2 g → 4 T 1g (F), 4 A 2g → 4 T 2g and the spin forbidden 4 A 2g → 2 T 1g , 2 E which is well-known for the [Cr (C 2 O 4 ) 3 ] 3– ion. , The two expected transitions of Co­(III) octahedra ( 1 A 1g → 1 T 1g and 1 A 1g → 1 T 2g ) around 400 and 500 nm are certainly masked by these intense bands of chromium­(III) ions.…”

Excited electronic states of MnO4−: Challenges for wavefunction and density functional response theories

“…In fact it involves a non-iterative doubles correction from perturbation theory to CCS and is therefore sometimes known as CC (2). This is analogous to the CCSDR(3) non-iterative triples correction to excitation energies relative to the CC3 model [9]. Interestingly the CIS(D) is qualitative and even semi-quantitative for the lowest LMCT excitation energies here.…”

“…Thus, despite the poor orbital description, and consequent large orbital relaxation the non-iterative variant of CC2 actually performs quite well, and the doubles correction uniformly lowers the excitation energies by $0.8-1 eV. We also note for completeness that the non-iterative CCSDR(3) approximation [9] to CC3 excitation energies gives 3.491 eV for the highly unphysical CC3 1 1 T 2 state.…”

“…We have previously shown how the supposedly simple TiO 2 molecule is challenging to describe [3]. The challenges when trying to accurately study the electronic excited states of transition metal complexes present a hurdle on the path to fully understanding the rich and varied reactive photochemistry that many transition metal complexes display, with more cases being reported regularly, see for example [4][5][6][7][8][9][10][11]. There are also a number of wellknown complexes that despite their modest size and simple structure have been classed as 'tough' examples when trying to fully understand the nature of their ground and electronic excited states due to often poor agreement between many theoretical methods and experiment [12].…”