Photodynamics of the Molecular Ruby [Cr(ddpd)2]3+

Abstract

The introduction of strong-field ligands can enable luminescence in first-row transition-metal complexes. In this way, earth-abundant near-infrared emitters can be obtained using early 3d metals. A prime example is the molecular ruby [Cr(ddpd)2]3+ (ddpd = N,N′-dimethyl-N,N′-dipyridin-2-ylpyridine-2,6-diamine) that can achieve high phosphorescence quantum yields at room temperature in aqueous solution. To understand these remarkable properties, here, we simulate its photodynamics in water using trajectory surface hopping on linear vibronic coupling potentials parametrized from multiconfigurational CASSCF/CASPT2 calculations. We find that after excitation to the second absorption band, a relaxation cascade through metal-centered states occurs. After an initial back-and-forth intersystem crossing with higher-lying doublet states, the complex relaxes through a manifold of quartet metal-centered states to the low-lying doublet metal-centered states which are responsible for the experimentally observed emission. These electronic processes are driven by an elongation of the Cr–ligand bond lengths as well as the twisting motion of the trans-coordinated pyridine units in the ddpd ligands. The low-lying doublet states are reached within 1–2 ps and are close in geometry to the doublet minima, thus explaining the high phosphorescence quantum yield of the molecular ruby [Cr(ddpd)2]3+.

Ferromagnetically Coupled Chromium(III) Dimer Shows Luminescence and Sensitizes Photon Upconversion

“…Back‐intersystem crossing from the emissive 2 T 1 / 2 E states to the 4 T 2 state in [Cr(dNinp) 2 ] 3+ seems difficult, due to the large ligand‐field splitting. For the energetically high‐lying 2 T 2 and 4 T 1 states, back‐ and forth intersystem crossing can in principle occur according to quantum chemical calculations performed for other Cr III complexes [44] . Transient UV‐vis absorption spectra of [Cr(dNinp) 2 ](OTf) 3 in aerated acetonitrile feature two negative signals centered at 355 nm and 425 nm (Figure 6a), corresponding to the bleach of the LMCT and mixed MC/LMCT absorption bands at these wavelengths (Figure 5a).…”

“…For the energetically high-lying 2 T 2 and 4 T 1 states, back-and forth intersystem crossing can in principle occur according to quantum chemical calculations performed for other Cr III complexes. [44] Transient UV-vis absorption spectra of [Cr(dNinp) 2 ](OTf) 3 in aerated acetonitrile feature two negative signals centered at 355 nm and 425 nm (Figure 6a), corresponding to the bleach of the LMCT and mixed MC/LMCT absorption bands at these wavelengths (Figure 5a). The transient absorption band centered at 520 nm is attributed to the typical excited state absorption of the 2 T 1 / 2 E states.…”

Computational Screening of Photodynamics of Transition-Metal Complexes

“…[22][23][24] In this light, the combination of potentials parametrized using the vibronic coupling model 25 and trajectory surface hopping (SH) for nonadiabatic molecular dynamics simulations 26 has become an affordable pathway to investigate photodynamics, 27,28 in particular of transition-metal complexes. [29][30][31][32][33][34][35][36] In vibronic coupling theory, the potential energy surfaces are expressed in Taylor expansion around a reference geometry in a basis of diabatic electronic states and a set of nuclear coordinates, for which typically the harmonic normal modes of the reference geometry are used. Using a linear vibronic coupling (LVC) approach, where only first-order terms are included, the model can be parametrized from a single-point calculation including gradients, non-adiabatic couplings and spin-orbit couplings.…”

“…were calculated at the triplet ground-state geometry at the CASSCF level of theory. Finally, vertical excitation energies were calculated at the quartet ground-state geometry at the CASPT2 level of theory 29. …”

Vitality of Intralayer Vibration in hBN for Effective Long-Range Interlayer Hole Transfer across High Barriers in MoSe2/hBN/WSe2 Heterostructures

“…Aiming to explore detailed interlayer hole transfer processes from the MoSe 2 to the WSe 2 upon the photoexcitation, a set of NAMD simulations accompanied with the “neglect of back-reaction” approximation (also known as the “classical path approximation”), powerful tools for revealing ultrafast dynamics of the photoreaction, , charge transfer, − charge recombination, and charge transport − upon photoexcitation in molecular and periodic systems, are conducted for H 0L , H 1L , H 2L , and H 3L configurations at a temperature of 100 K (denoted as H 0L -100K, H 1L -100K, H 2L -100K, and H 3L -100K, respectively). Besides, the temperature effect has been examined by performing another simulation for H 3L at a temperature of 300 K (H 3L -300K) (Figure ) (details are listed in Supporting Information).…”