Excited-state dynamics of [Mn(im)(CO)3(phen)]+: PhotoCORM, catalyst, luminescent probe?

Abstract

Mn(I) -diimine carbonyl complexes have shown promise in the development of luminescent CO release materials (photoCORM) for diagnostic and medical applications due to their ability to balance the energy of the low-lying metal-to-ligand charge transfer (MLCT) and metalcentered (MC) states. In this work, the excited state dynamics of [Mn(im)(CO)3(phen)] + (im = imidazole; phen = 1,10-phenanthroline) is investigated by means of wavepacket propagation on the potential energy surfaces associated to the eleven low-lying Sn singlet excited states within a vibronic coupling model in a (quasi) diabatic representation including sixteen nuclear degrees of freedom. The results show that the early time photophysics (< 400 fs) is controlled by the interaction between two MC dissociative states, namely S5 and S11, with the lowest S1-S3 MLCT bound states. In particular, the presence of S1/S5 and S2/S11 crossings within the diabatic picture along the Mn-COaxial dissociative coordinate (qMn-COaxial) favours a twostepwise population of the dissociative states, at about 60-70 fs (S11) and 160-180 fs (S5), that reaches about 10% within 200 fs. The one-dimensional reduced densities associated to the dissociative states along qMn-COaxial as function of time clearly point to concurrent primary processes, namely CO release vs. entrapping into the S1 and S2 potential wells of the lowest luminescent MLCT states within 400 fs, characteristics of luminescent photoCORM.

The Quest to Simulate Excited-State Dynamics of Transition Metal Complexes

“…Compared to MC/MR, SR methods feature a considerably lower scaling in the computational cost with regard to the system size, making them more amenable to transition metal complexes. Applications revolve around (closed-shell) low-spin d 6 complexes ,,− and d 10 systems − with one single exception . As a further advantage, SR methods can be considered more “black box” than MC/MR methods as they typically depend on fewer (and less critical) parameters, which makes them more user-friendly.…”

The quest to simulate excited-state dynamics of transition metal complexes

“…139,140. This preference is also mirrored in excited state dynamics studies, that mostly rely on hybrid functionals 32,38,[107][108][109][110][111][112][113][114][115][116][117][118][119][120]126,[128][129][130][131] with some exceptions. [121][122][123][124]129 In addition to the general functional dependence, TDDFT is well known to suffer from its inability to describe CT excitations with standard XC functionals.…”

“…Despite these limitations, LVC has become the standard approach to calculate PES in wave-packet dynamics simulations using MCTDH for transition metal complexes 38,91,[106][107][108][109][110][112][113][114][115][116][126][127][128]130 making it possible to include up to 16 nuclear degrees of freedom. 126 One example of MCTDH using 15 degrees of freedom in a heme-CO complex is shown in Figure 5. Among these studies, it is worth to mention that only two include explicitly the excitation by a laser pulse.…”

“…One approach thereby is to select normal modes based on the size of their vibronic coupling terms. 110,126,127,171 As large vibronic coupling elements are needed to efficiently transfer population between the electronic states, these coupling modes are necessary to describe the excited-state dynamics. This selection can be extended by adding tuning modes, which are normal modes that are responsible for the largest displacements in the excitedstate dynamics by reaching towards the excited-state minima 38,[113][114][115][116] and the excited-state crossing points.…”

“…These models have been applied in excited-state dynamics of solvated transition metal complexes parameterized with LVC potentials using both, MCTDH [107][108][109][110][111][112]116,126,128 and AIMD simulations. [117][118][119]132 Although, in principle, there exist stationary studies where also biological environments are approximately modelled with continuum models with very small dielectric constants, such strategy has not been used for dynamics, as it cannot capture the explicit fluctuations of the complex environments.…”