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RESONANCE RAMAN SPECTRA OF THE II‐CATION RADICALS OF COPPER, COBALT, AND NICKEL METHYLOCTAETHYLCHLORINS: VIBRATIONAL CHARACTERISTICS OF CHLOROPHYLL MODELS
Author(s) -
Salehi Asaad,
Oertling Nthony,
Fonda AroldN.,
Babcock Erald T.,
Chang C. K.
Publication year - 1988
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1988.tb02856.x
Subject(s) - raman spectroscopy , porphyrin , chemistry , chlorin , radical , photochemistry , nickel , resonance (particle physics) , copper , cobalt , molecular vibration , spectral line , crystallography , molecule , inorganic chemistry , organic chemistry , physics , particle physics , astronomy , optics
— By using excitation at 363.8 nm, resonance Raman (RR) spectra were obtained for Cu(II), Co(II), and Ni(II) complexes of methyloctaethylchlorin (MeOEC) and their ir‐cation radicals. Additionally, the Raman spectra of the Cu(II) derivatives of (rarcs‐octaethylchlorin (r‐OEC) were included for comparison. The alkyl‐substituted CuMeOEC exhibits a Raman spectrum that is nearly identical to that of the simpler (‐CuOEC in both the neutral and oxidized states. Unlike the latter species, the cation radical of CuMeOEC is immune to oxidative dehydrogenation to porphyrin, and this has facilitated vibrational characterization of the ring‐oxidized species. This study aims to compare the vibrational characteristics in the 1450 to 1700 cm ‐t region of the metallochlorin ir‐cation radicals to those of the corresponding oxidized metalloporphyrins. We focus on two modes in the1500–1520 cm ‐1 and1620–1650 cm ‐1 region that are analogous to the v 3 and v 10 vibrations, respectively, in the metalloporphyrin analogs. These vibrational modes are clearly defined in all species and exhibit a strong core‐size dependency in the porphyrin complexes. The core‐size study as well as the frequency changes upon oxidation support the conclusion that the v 3 ‐like vibration in the chlorin species features substantial C b C b in addition to C a C m stretching character. The v, 0 ‐like mode of the chlorin macrocycle, on the other hand, displays characteristics that closely resembles that of the porphyrin analog; consequently, these vibrations are of predominantly C a C m stretching character in both cases.