Studies of the vibrational and electronic structure of the S{sub 1} excited states of {beta}-substituted porphyrins by picosecond time-resolved resonance Raman spectroscopy

Journal Article · Thu Apr 20 04:00:00 EDT 1995 · Journal of Physical Chemistry

DOI:https://doi.org/10.1021/j100016a014· OSTI ID:45002

Kumble, R; Loppnow, G R; Hu, S; Mukherjee, A; Spiro, T G ^[1]; Thompson, M A ^[2]

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1. Princeton Univ., NJ (United States)
2. Pacific Northwest Lab., Richland, WA (United States)

Resonance Raman (RR) spectra are reported for the S{sub 1} excited states of zinc(II) complexes of octaethylporphyrin (OEP) and protoporphyrin-IX-dimethyl ester (PPDME). Skeletal stretching modes exhibit large downshifts in the S{sub 1} state of ZnOEP relative to the ground state, indicating an overall expansion of the macrocycle upon photoexcitation. Vibrational modes are assigned using {sup 15}N and meso-d{sub 4} isotopomers of OEP: the isotopic sensitivity is observed to be similar in the S{sub 0} and S{sub 1} states, implying that the ground-state normal mode structure is preserved in the singlet excited state. Excited-state bond orders are calculated using INDO1/S methods. The frequency shift patterns for skeletal vibrational modes of ZnPPDME in the S{sub 1} excited state closely resemble those of ZnOEP, implying a similar electronic configuration; the vinyl C=C stretching mode appears to be only slightly perturbed in the excited states, although the exact position cannot be accurately determined. The results of these studies support the description of metalloporphyrin singlet excited states provided by Gouterman`s four-orbital model. 69 refs., 9 figs., 3 tabs.

• Sponsoring Organization: USDOE
• DOE Contract Number: AC02-81ER10861; AC06-76RL01830
• OSTI ID: 45002
• Journal Information: Journal of Physical Chemistry, Journal Name: Journal of Physical Chemistry Journal Issue: 16 Vol. 99; ISSN JPCHAX; ISSN 0022-3654
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
99 GENERAL AND MISCELLANEOUS
ABSORPTION SPECTRA
CHEMICAL BONDS
ELECTRONIC STRUCTURE
EXCITED STATES
GROUND STATES
MOLECULAR ORBITAL METHOD
PORPHYRINS
PROTOPORPHYRINS
RAMAN SPECTRA
RAMAN SPECTROSCOPY
VIBRATIONAL STATES
ZINC COMPLEXES