Energy Dependence of the Ruthenium(II)-Bipyridine Metal-to-Ligand-Charge-Transfer Excited State Radiative Lifetimes: Effects of ππ*(bipyridine) Mixing

Abstract

The variations in band shape with excited state energy found for the triplet metal to ligand charge transfer ((3)MLCT) emission spectra of ruthenium-bipyridine (Ru-bpy) chromophores at 77 K have been postulated to arise from excited state/excited state configurational mixing. This issue is more critically examined through the determination of the excited state energy dependence of the radiative rate constants (kRAD) for these emissions. Experimental values for kRAD were determined relative to known literature references for Ru-bpy complexes. When the lowest energy excited states are metal centered, kRAD can be anomalously small and such complexes have been identified using density functional theory (DFT) modeling. When such complexes are removed from the energy correlation, there is a strong (3)MLCT energy-dependent contribution to kRAD in addition to the expected classical energy cubed factor for complexes with excited state energies greater than 10 000 cm(-1). This correlates with the DFT calculations which show significant excited state electronic delocalization between a π(bpy-orbital) and a half-filled dπ*-(Ru(III)-orbital) for Ru-bpy complexes with (3)MLCT excited state energies greater than about 16 000 cm(-1). Overall, this work implicates the "stealing" of emission bandshapes as well as intensity from the higher energy, strongly allowed bpy-centered singlet ππ* excited state.

Promoting Intersystem Crossing of a Fluorescent Molecule via Single Functional Group Modification

“…[7][8][9][10][11][12][13][14] In organometallic LEDs, for instance, the interaction between the singlet metal-to-ligand charge transfer ( 1 MLCT) and the lowest triplet metal-to-ligand charge transfer ( 3 MLCT) states leads to robust ISC, resulting in high phosphorescence quantum yield. [15][16] To date, many phosphorescent molecules are either organometallic molecules or organic molecules with halogen atoms. [17][18] Such dominance has two causes, both well-documented.…”

“…Molecular phosphorescence has a high potential in information processing applications, including sensors, biological imaging, and LEDs, which has promoted a vivid search for efficient, low-cost, and environment-friendly phosphorescent materials. − Naturally, a crucial point in this search is to develop molecules with efficient intersystem crossing (ISC), the nonradiative transition between electronic states with different spin multiplicity. − In organometallic LEDs, for instance, the interaction between the singlet metal-to-ligand charge transfer ( 1 MLCT) and the lowest triplet metal-to-ligand charge transfer ( 3 MLCT) states leads to robust ISC, resulting in high phosphorescence quantum yield. , …”

Metal-to-Ligand Charge-Transfer Emissions of Ruthenium(II) Pentaammine Complexes with Monodentate Aromatic Acceptor Ligands and Distortion Patterns of their Lowest Energy Triplet Excited States

“…These observations suggest a basis for selecting Ru photosensitizers with lower energy 3 MLCT than 3 MC excited states: the 77 K MLCT emission maximum of the sensitizer should have a lower energy than the energy for breaking both Ru−ligand bonds along the weakest bonding axis. 21 The point for [Ru(bpy) 3 ] 2+ is based on 3 MC calculations reported by Sun et al, 15 and 77 K emission spectra reported by Thomas et al 21 The code numbers in panel A are from The Supporting Information is available free of charge on the…”

Isolation and Structural Elucidation of 15‐Nuclear Copper Dihydride Clusters: An Intermediate in the Formation of a Two‐Electron Copper Superatom

“…The chemistry of transition-metal hydride clusters has recently received significant interest. [1,2] Such compounds play a key role as intermediates in several homogeneous and heterogeneous catalyses [3] with significant contributions in hydrogen storage. [4] Importantly, copper hydride chemistry has evolved towards the design of nanosized ligand-protected polyhydrido copper clusters that have emerged as a new class of materials in the field of nanoscience, owing to their various potential applications.…”

“…Received: ((will be filled in by the editorial staff)) Revised: ((will be filled in by the editorial staff)) Published online: ((will be filled in by the editorial staff)) ), Triethylamine and phenylacetylene were prepared as described in the literature. [1][2][3] Solvents were purified following standard protocols. Melting points were measured by using a Fargo MP-2D melting point apparatus.…”