Picosecond transient resonance Raman study on the excited‐state conformational dynamics of a highly ruffled nickel porphyrin

Abstract

Picosecond to nanosecond transient resonance Raman spectroscopy was applied to track down the excitedstate conformational excursions of Ni II T(t-Bu)P [nickel(II) 5,10,15,20-tetra-tert-butylporphyrin] in various solvents with different dielectric properties. From the resonance Raman spectra of Ni II T(t-Bu)P obtained by picosecond pulse photoexcitation, the a 4 -type conformer was suggested to be dominant in the 1 (d,d) excited state at the initial stage of deactivation processes (∼3 ps). However, only one conformer of abab type was found to persist on the nanosecond time-scale. We also observed that the initial formation of the 1 (d,d) excited state of Ni II T(t-Bu)P from the 1 .p, p * / excited state is independent of the solvent, but the subsequent decay of the 1 (d,d) to the ground state is strongly solvent dependent.

Ultrafast Excited State Relaxation of a Metalloporphyrin Revealed by Femtosecond X-ray Absorption Spectroscopy

“…This state has a 3d electronic configuration of (3d x2-y2 ) 1 (3d z2 ) 1 and is here denoted T(d,d) (Figure 1). 41,47 A pump-pump-probe transient absorption measurement of Ni(II) porphyrin excited state dynamics suggested that a transient Ni(I) charge transfer state may exist with a lifetime of a few picoseconds, 40 but previously such a reaction pathway could not be substantiated by monitoring the temporal evolution of the nickel electronic configuration. In comparison to these previous optical and vibrational spectroscopic studies, X-ray transient absorption (XTA) spectroscopy, 22,23 which combines a laser excitation and conventional X-ray absorption spectroscopy, 48 can directly probe the metal center electronic structure and local geometry rather than relying on the indirect deduction of excited state dynamics from relatively broad transient optical spectral features.…”

X-ray snapshots for metalloporphyrin axial ligation

“…The metalloporphyrin chosen in our study was Ni(II) tetramesitylporphyrin (NiTMP). Molecular dynamics and structures of nickel(II) porphyrins were extensively studied by ultrafast transient absorption spectroscopy, [4][5][6][7][8][9][10][11] resonance Raman spectroscopy, [12][13][14][15][16][17][18][19][20] X-ray transient absorption spectroscopy [21][22][23][24][25] and quantum mechanical calculations. [25][26][27][28][29] Together, these studies showed severe non-planar distortions of the porphyrin macrocycle due to a mismatch of the smaller Ni(II) ion with the larger porphyrin macrocycle to which the Ni(II) was coordinated.…”

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

“…One metalloporphyrin studied by XTA was Ni(II) tetramesitylporphyrin (NiTMP), whose analogs were previously investigated by ultrafast TA [29][30][31][32][33][34][35][36], resonance Raman spectroscopy [37][38][39][40][41][42][43][44][45], previous XTA measurements [18,[46][47][48][49] and quantum mechanical calculations [49][50][51][52][53] due to their rich photochemical reaction pathways which can be used to understand similar processes in other metalloporphyrins (Fig. 1).…”