Photodynamics of nickel porphyrins in noncoordinating solvents: characterization of d-d excited states using transient raman spectroscopy

Journal Article · Thu Jan 28 04:00:00 EST 1988 · J. Phys. Chem.; (United States)

DOI:https://doi.org/10.1021/j100313a014· OSTI ID:5365826

Findsen, E W; Shelnutt, J A; Ondrias, M R

The photodynamic behavior of several nickel porphyrins in noncoordinating solvents was investigated with absorption and transient Raman spectroscopies. A recent transient absorption study of nickel porphyrins, in noncoordinating solvents proposed that, upon photoexcitation from the ground 4-coordinate state (/sup 1/A/sub 1g/), the excited-state decay path traverses a state in which the metal is in an electronic state (designated here as *B/sub 1g/) similar to that observed for the metal in coordinating solvent systems (/sup 3/B/sub 1g/). This excited state involves the net promotion of one of the two nickel electrons in the d/sub z2/ orbital into the empty d/sub x2-y2/ orbital. While the lifetime of the *B/sub 1g/ state has been estimated to be approx. 250 ps, it can be observed by using approx. 10-ns-wide laser pulses under appropriate experimental conditions. Simple calculations demonstrate the effect of state lifetimes upon the population of the excited-sate species within the nanosecond laser pulse. The *B/sub 1g/ state is reversibly formed for several nickel porphyrins in all noncoordinating solvents used. This state is identified in transient Raman spectra by shifts in several lines. Three of these lines are sensitive to changes in the core size of the porphyrin and indicate expansion of the porphyrin core to accommodate the increased in-plane electron density caused by the electron promotion on the metal. Detailed examination of one nickel porphyrin, NiPPDME, indicates a dependence of the *B/sub 1g/ state's vibrational characteristics upon the solvent environment and implies that the porphyrin a/sub 2u/ orbital is very sensitive to solvent environment. Absorption studies indicate that while both the a/sub 1u/ and a/sub 2u/ orbitals can be influenced by the solvent environment, the a/sub 2u/ orbital is the most affected.

• Research Organization: Univ., of New Mexico, Albuquerque
• DOE Contract Number: AC04-76DP00789
• OSTI ID: 5365826
• Journal Information: J. Phys. Chem.; (United States), Journal Name: J. Phys. Chem.; (United States) Vol. 92:2; ISSN JPCHA
• Country of Publication: United States
• Language: English

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CARBOXYLIC ACIDS
CHEMICAL REACTIONS
CHEMISTRY
DATA
ENERGY LEVELS
EXCITED STATES
EXPERIMENTAL DATA
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
INFORMATION
LASER SPECTROSCOPY
LASERS
LIFETIME
NEODYMIUM LASERS
NICKEL COMPOUNDS
NUMERICAL DATA
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHOTOCHEMISTRY
PORPHYRINS
RAMAN SPECTROSCOPY
SOLID STATE LASERS
SPECTROSCOPY
TRANSITION ELEMENT COMPOUNDS