Ultrafast Stimulated Emission and Structural Dynamics in Nickel Porphyrins

Abstract

The excited-state structural dynamics of nickel(II)tetrakis(2,4,6-trimethylphenyl)porphyrin (NiTMP) and nickel(II)tetrakis(tridec-7-yl)porphyrin (NiSWTP) in a toluene solution were investigated via ultrafast transient optical absorption spectroscopy. An ultrashort stimulated emission between 620 and 670 nm from the S1 state was observed in both nickel porphyrins only when this state was directly generated via Q-band excitation, whereas such a stimulated emission was absent under B (Soret)-band excitation. Because the stimulated emission in the spectral region occurs only from the S1 state, this photoexcitation-wavelength-dependent behavior of Ni(II) porphyrins is attributed to a faster intersystem crossing from the S2 state than the internal conversion S2 --> S1. The dynamics of the excited-state pathways involving the (pi, pi*) and (d, d) states varies with the meso-substituted peripheral groups, which is attributed to the nickel porphyrin macrocycle distortion from a planar configuration. Evidence for intramolecular vibrational relaxation within 2 ps and vibrational cooling in 6-20 ps of a (d, d) excited state has been established for NiTMP and NiSWTP. Finally, the lifetimes of the vibrationally relaxed (d, d) state also depend on the nature of the peripheral groups, decreasing from 200 ps for NiTMP to 100 ps for the bulkier NiSWTP.

A cascade through spin states in the ultrafast haem relaxation of met-myoglobin

“…The SAS of the Mb * I state has a maximum between 430 and 450 nm and, at longer wavelengths, a broad and unstructured absorption extending beyond 650 nm. Very similar features were observed in the singlet and triplet (π , π *) free-base and Zn-porphyrin excited states, 28 in the transients of other metallo-porphyrins, 28,29 as well as in freebase and metallo-porphyrin cations. [30][31][32] Within the same free-base or metallo-porphyrin compound, the singlet, triplet, and π -cation states show similar enhanced absorption on the red side of the Soret band, whose peak position differs by a few tens of nm, as well as a weak and broad absorption which extends from 500 nm to the IR.…”

Photo-Induced Pyridine Substitution in cis-[Ru(bpy)2(py)2]Cl2: A Snapshot by Time-Resolved X-ray Solution Scattering

“…10,19 In the last few years, time-resolved XAS (X-ray Absorption Spectroscopy) has been successfully employed for studying excited-state structures in solution, as demonstrated by the work of several authors. [20][21][22][23][24][25] Direct observation of structural dynamics with atomic resolution can be also obtained by TR-WAXS (Time-Resolved Wide Angle X-ray Scattering). This young technique has been used to characterize light-induced structural changes in solution for a variety of systems ranging from diatomic molecules 26 to large biomolecules.…”

Short‐time photodecay dynamics of meso‐tetra(p‐hydroxyphenyl)porphine in the condensed phase explored via resonance Raman spectroscopy and density functional theory calculation

“…Subsequent publication present further analysis of the data. [33,37] The dramatic decrease of the time constant from ∼50 fs in ZnTPP [7] as well as in other metalloporphyrins [37] to 10 fs in THPP is related to the decrease of the energy gap E(B x − B y ) between electronic states. According to the energy gap law, the time constant increases exponentially with increasing energy gap.…”