New insight into metalloporphyrin excited state structures and axial ligand binding from X-ray transient absorption spectroscopic studies

The Nature of the Long‐Lived Excited State in a NiII Phthalocyanine Complex Investigated by X‐Ray Transient Absorption Spectroscopy

“…However,t he probed excited state of NiPcOBu 8 in this study revealed two pre-edge features arising at 8332 and 8334.5 eV, indicated by the difference spectrum as well as the extracted excited state spectrum.T his hints that the excited state probeda t1 00 ps after the 400 nm excitation is not ofaLMCT nature, but rather a( d,d) state in which both the 3d z 2 and 3d x 2 Ày 2 orbitals are singly occupied (Figure 6, right). [17][18][19] The blueshift of the 1s!4p z peak in the excited state also supported its assignment as a( d,d) state. [17][18][19] The blueshift of the 1s!4p z peak in the excited state also supported its assignment as a( d,d) state.…”

“…The ultrafastX TA study on NiTMP [19] found that the short-lived LMCT state exhibited ar edshifted1 s !4p z peak compared to that of the ground state. [17][18][19] The Ni 3d x 2 Ày 2 orbital has metal-ligand s antibonding character in the square-planar coordination geometry of tetrapyrrolic complexes. (a) XANES spectraofN iPcOBu8, along with the enlarged pre-edger egion in the inset.…”

“…The capability of XTAt os imultaneouslyt rack electronic and structural factors was well demonstrated in our previous work on Ni II tetramesitylporphyrin (NiTMP). [17][18][19] Following the Q-band excitation that promotes macrocycle-based p!p *t ransitions, NiTMP in noncoordinating solvents shows rapid radiationless decay of the initial excited (p, p*) state through low-lying intermediate states of (p,d x 2 Ày 2 )a nd (d z 2 ,d x 2 Ày 2 ), successively,t o The nature of the photoexcited state of octabutoxy nickel(II) phthalocyanine (NiPcOBu 8 )w ith a5 00 ps lifetimew as investigated by X-ray transienta bsorption (XTA) spectroscopy.P revious optical, vibrational, and computational studies have suggested that this photoexcited state has al igand-to-metal charge transfer (LMCT) nature. By using XTA, which provides unambiguous information on the local electronic and nuclear configuration around the Ni center,t he nature of the excited state of NiPcOBu 8 was reassessed.…”

Observing heme doming in myoglobin with femtosecond X-ray absorption spectroscopy

“…An experimental technique potentially able to monitor the structural changes at the heme with fs time resolution is X-ray absorption spectroscopy (XAS). Indeed, X-ray Absorption Near Edge Structure (XANES) spectroscopy is very sensitive to both the electronic distribution and the position of the nuclei around the absorbing metal (Lima et al , 2014; Shelby et al , 2014). In particular, it has been shown that the Fe(II) K-edge XANES spectrum of MbCO photoproduct is sensitive to the distances and bond angles around the heme iron (Della Longa et al , 2001; Arcovito et al , 2005) and that one of the most relevant parameters affecting the spectrum shape is the distance between the Fe and the N ε of the proximal histidine (Arcovito et al , 2005).…”

Elucidating the Ultrafast Dynamics of Photoinduced Charge Separation in Metalloporphyrin-Fullerene Dyads Across the Electromagnetic Spectrum

“…[27][28][29][30][31][32][33][34][35][36][37] Being element-specific and applicable to any state of matter, time-resolved X-ray absorption spectroscopy (TR-XAS) is a rapidly maturing technique capable of delivering unique information about the electronic and geometric structures of metastable photoexcited states with picosecond and femtosecond temporal resolution. [38][39][40][41][42][43][44][45][46] Recently, it has been applied as a complementary analytical tool to investigate the decay pathways in laser-excited MPs and the early steps of CO and NO ligation/deligation in hemelike porphyrins relevant for respiration. 47,48 In the present work, TR-XAS is employed in combination with ultrafast time-resolved optical absorption spectroscopy (TR-OAS) in the near infra-red and the visible regions in order to clarify the ultrafast dynamics within a prototypical Cu II P following light absorption and to elucidate several unexpected aspects of the photoinduced intramolecular ET in a related Cu II P-C 60 dyad.…”