Trapping intermediate MLCT states in low-symmetry {Ru(bpy)} complexes

Abstract

The picosecond excited state dynamics of [Ru(tpm)(bpy)(NCS)]+ (RubNCS+) and [Ru(tpm)(bpy)(CN)]+ (RubCN+) (tpm = tris(1-pyrazolyl)methane, bpy = 2,2′-bipyridine) reveal an intermediate MLCT excited state living in the 300 ps timescale.

A Hole Delocalization Strategy: Photoinduced Mixed-Valence MLCT States Featuring Extended Lifetimes

“…19 A very similar differential absorption spectrum was gathered for an excited state with the hole repelled from the z-axis in Ru(NCS) + . 22 Together, these observations are in line with the proposed {Ru III (tpm)(bpy − )(μNC)Ru II (L) 4 (CN)} configuration for this state. Kinetic Model and Excited State Lifetimes.…”

“…Here, the negative signal is masked by much stronger photoinduced LMCT (PILMCT) transitions in the same spectral region, in sound agreement with observations on the {Ru(tpm)(bpy)} fragments. 22 Further examination of the ns-TAS data reveals the nature of another ns-lived state, as suggested by TCSPC experiments. Global target analyses of the transient absorption data (Tables S1 and S2) were performed by means of the kinetic model shown in Figure S7: two coexisting species, which both decay to the GS, as one of them transforms into the other.…”

“…21 In contrast, the emission in the monometallic Ru(NCS) + reference stems from a single state regardless of the excitation wavelength. 22 In other words, the presence of a second metal center seems responsible for an additional emitting state in bimetallic RuRu(py) 2+ and RuRu(MeOpy) 2+ . Despite the higher density of vibrational states that are present in bimetallic RuRu(py) 2+ and RuRu(MeOpy) 2+ , their emission lifetimes are, however, longer than those in monometallic Ru(NCS) + .…”

“…The spectroscopic signature is a strong photoinduced dπ(Ru) ← π(NCS) LMCT absorption at 16,500 cm −1 (600−610 nm) (Figure 3). 22 For 3 MLCTz in RuRu(py) 2+ and RuRu-(MeOpy) 2+ , the lowest energy photoinduced fingerprint is ascribed to a PIIVCT transition. 17 The latter is centered at 8100 cm −1 (1230 nm) for RuRu(MeOpy) 4− and 8800 cm −1 (1150 nm) for RuRu(py) 2+ .…”

Inversion of donor–acceptor roles in photoinduced intervalence charge transfers

“…The photoinduced absorptions at n 4 23 000 cm À1 (peaking at 24 800 cm À1 as observed in the nanosecond experiments) are ascribed to radical anion-centered p* ' p* transitions, while those between 13 000 and 17 000 cm À1 correspond to radical anion-centered p* ' p* transitions and dp(Ru) ' p* photoinduced LMCT bands. 44,45 The energy of these signals remains essentially unchanged upon changing the nature of the M ion, although a strong photoinduced absorption in the spectrum of RuFe 2À is detected at 16 450 cm À1 . We assign it as a dp(Ru) ' p(CN) PILMCT transition from the cyanide bridge, which appears more to the red, and hence resolved from the bleach, for this complex since Fig.…”