Direct Observation of Competitive Ultrafast CO Dissociation and Relaxation of an MLCT Excited State:  Picosecond Time-Resolved Infrared Spectroscopic Study of [Cr(CO)₄(2,2‘-bipyridine)]

Abstract

Early excited-state dynamics of [Cr(CO)(4)(bpy)] were studied in a CH(2)Cl(2) solution by picosecond time-resolved IR spectroscopy, which made it possible to characterize structurally the individual species involved and to follow separately the temporal evolution of the IR bands due to the bleached ground-state absorption, the fac-[Cr(CO)(3)(Sol)(bpy)] photoproduct, and two (3)MLCT states. It was found that the fac-[Cr(CO)(3)(Sol)(bpy)] photoproduct is formed alongside population of two (3)MLCT states during the first picosecond after excitation at 400 or 500 nm by a branched evolution of the optically populated excited state. Vibrationally relaxed (3)MLCT excited states are unreactive, decaying directly to the ground state on a picosecond time scale. The photoproduct is long-lived, persistent into the nanosecond time domain. Changing the excitation wavelength from 400 to 500 nm strongly increases the extent of the bleach recovery and decreases the yield of the photoproduct formation relative to the initial yield of the population of the unreactive (3)MLCT states. The photochemical quantum yield of CO dissociation also decreases with increasing excitation wavelength (Víchová, J.; Hartl, F.; Vlcek, A., Jr. J. Am. Chem. Soc. 1992, 114, 10903). These observations demonstrate the relationship between the early dynamics of optically populated excited states and the overall outcome of a photochemical reaction and identify the limiting role of the branching of the initial excited-state evolution between reactive and relaxation pathways as a more general principle of organometallic photochemistry.

Theoretical characterization of ruthenium complexes containing functionalized bithiophene ligands for dye-sensitized solar cells

“…This can be testified by the calculated angle of N1eRueN3 (99.9 ) and N2eRueN5 (172.1 ), far from the ideal values of 90.0 and 180.0 for an octahedral complex. The bite-angles of N1eRueN2 and N3eRueN4, which play an important role in determining the photophysical properties of Ru complexes [31,32], fall in the range of 78.1 e79.1 calculated with both basis sets. For the gas phase CYCeB11, bond lengths of RueN concerning SCN, dcbpy, and btpfunctionalized bipyridine (bpy) ligands are calculated to be w2.04, w2.06, and w2.08 Å, respectively.…”

Manganese(I)‐Catalyzed C−H Activation: The Key Role of a 7‐Membered Manganacycle in H‐Transfer and Reductive Elimination

“…[10] We hypothesized that UV irradiation [11] of 2g would lead to solvated intermediate I Pyr (Scheme 2, middle inset). [12] Subsequent alkyne trapping via intermediate II Pyr ,w ould then convert into the alkyne insertion manganacycle 4g.UV irradiation (Hg/Xe Arc lamp,2 00-2500 nm) of am ixture of 2g and 3 (1.1 equiv) in [D 8 …”

“…[10] We hypothesized that UV irradiation [11] of 2g would lead to solvated intermediate I Pyr (Scheme 2, middle inset). [12] Subsequent alkyne trapping via intermediate II Pyr ,w ould then convert into the alkyne insertion manganacycle 4g.UV irradiation (Hg/Xe Arc lamp,2 00-2500 nm) of am ixture of 2g and 3 (1.1 equiv) in [D 8 ]THF at 240 K(at 5min intervals), and reaction monitoring by 1 HNMR spectroscopy between intervals,r evealed the formation of an ew intermediate that grows up to 9.6 %conversion. Further irradiation resulted in spectral broadening (paramagnetic species), but crucially,full NMR analysis of manganacycle 4gwas possible,with HMQC/ HMBC correlation methods/n.O.e.e xperiments.A nalysis shows that 4g formed regioselectively at C3 (Scheme 2, bottom inset).…”

Time-Resolved Relaxation Studies of Spin Crossover Systems in Solution

“…Time-resolved infrared (TRIR) spectroscopy, already well established as a technique in the general area of metal complex and organometallic photochemistry and photophysics throughout the time range ms-ps, has not so far been applied to study of SCO dynamics. However, a recent report [43] by picosecond TRIR of MLCT excited state relaxation in Cr(0) complexes points to its promise in the SCO field also, particularly since the technique enables vibrational modes of complexes to be directly probed without the requirement for resonance with vibronic transitions, as is the case with the TR 3 method.…”