Picosecond Time-Resolved Resonance Raman Scattering from Zinc(II) Octaethylporphyrin

Kreszowski, Douglas H.; Deinum, Geurt; Babcock, Gerald T.

doi:10.1021/ja00095a082

Cited by 19 publications

(17 citation statements)

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“…The broadness of the features in the T I ZnTPC spectrum are intrinsic to this excited state and do not result from product decomposition, as "probeonly" spectra obtained after the pump-pulse spectra are identical to the original ground state spectra. Broad features have also been reported for the T I state of ZnTPP22 and ZnOEP.11, 31 We tentatively assign the breadth of the bands to overlapping contri'htions from multiple modes, which become activated as a result of bond order changes in the T I state, as discussed below for v4. Another possibility is that photoexcitation alters the axial ineractions of the Zn metal with solvent molecules, producing heterogenous broadening, but changing the solvent to DMF does not produce noticeable spectral changes.…”

supporting

confidence: 64%

Resonance Raman characterization of the triplet state of zinc tetraphenylchlorin

Vitols¹,

Terashita²,

Blackwood³

et al. 1995

J. Phys. Chem.

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The TI excited state of zinc(I1) tetraphenylchlorin, ZnTPC, has been studied by nanosecond time-resolved transient absorption (TA) and transient resonance Raman (TR3) spectroscopy. The TA difference spectrum shows an induced absorption at 450 nm that is assigned as arising from a 3 (~, n * ) state. The most striking feature of the 3(ZnTPC) TR3 spectrum is the significant frequency downshifts and strong intensity enhancements of the pyrrole half-ring stretch, v4, and of other pyrrole ring motions which together produce a broad band in the 1150-1300-~m-~ region. In addition, the enhancement of C,C, modes (~2 and V I I ) changes with their phasing between the SO and TI states. Weaker intensity enhancements, with no frequency shifts, are seen for the phenyl substituent ring mode, 0 4 and V I , and C,-phenyl stretch. These findings suggest that there is less electronic participation from the phenyl rings in the resonant triplet state, T,, for ZnTPC than for its parent metalloporphyrin, ZnTPP.The excited states of metalloporphyrins and metallochlorins play an integral role in biological energy and electron transfer, photodynamic therapy, and photocatalysi~.'-~ The lowest-lying excited states of metalloporphyrins have been studied by resonance Raman (RR)6a-C and resonance coherent anti-Stokes Raman'"-' (RCAR) spectroscopy in order to obtain detailed structural information on the excited states. In comparison to metalloporphyrins, far less is known about the excited state dynamics of metallochlorins. Although ground state absorption, resonance Raman, and infrared spectra of metallochlorins have been studied in some detail,8-'s there have been few reports dealing with their excited state spectra.Hydroporphyrins such as ZnTPC (TPC = tetraphenylchlorin) represent a distinct class of biologically relevant compounds.16-'8 The reduction of one pyrrole ring in the chlorin macrocycle lowers the symmetry from D4h to Czv, resulting in further separation of the highest occupied molecular orbitals, HOMOS, and a loss of degeneracy in the lowest unoccupied molecular orbitals, LUMOs. The electronic and structural changes alter the photophysical, redox, and ligand-binding properties of metallochlorins relative to those of the parent metalloporphyrins.18a-b However, it is not clear how the reduction of the pyrrole ring affects the excited state dynamics of metallochlorins relative to metalloporhyrins. In order to address this question, we have investigated the character of the lowest-lying excited state of ZnTPC by transient absorption and TR3 spectroscopy.ZnTPC was purchased from Midcentury Chemical Co. (Posen, IL). Its punty was checked via thin layer chromatography. ZnTpC-d20 and ZnTPC-d8 isotopomers were synthesized according to standard literature preparation^.'^-*' The ZnTPC complexes were purified on 1000-pm silica gel plates (Analtech), using a degassed 3:l mixture of THF and hexane as eluant. The purification was done in a glovebox under an inert atmosphere (Vacuum Atmosphere Model D1-00 1-SD equipped with an He-493 Dri-Train). ...

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supporting

confidence: 64%

Resonance Raman characterization of the triplet state of zinc tetraphenylchlorin

Vitols¹,

Terashita²,

Blackwood³

et al. 1995

J. Phys. Chem.

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“…Our results contradict an earlier assertion, made on the basis of excitedstate resonance-Raman data, that JT distortions are weak or absent in the Q state of ZnOEP but are relatively strong in the P state. 34 The magnitude of the Q-state JT effect determined by moment analysis is twice that obtained by consideration of individual band intensities. The difference almost certainly arises from the presence of interstate vibronic (HT) coupling, which invalidates the approximations inherent in eq 19.…”

Section: Discussionmentioning

confidence: 93%

Magnetooptical Spectroscopy of Zinc Octaethylporphyrin in an Argon Matrix

Gasyna¹,

Metcalf²,

Schatz³

et al. 1995

J. Phys. Chem.

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Magnetic circular dichroism, magnetic circularly polarized luminescence, emission, and absorption spectra have been measured over the range 12 500-50 000 cm-' for zinc octaethylporphyrin isolated in an argon matrix at -6 K. The spectra arise from transitions at a single matrix site. Values of gll for the Q, B, and N states are 7.0 f 0.7, 1.0 f 0.3, and 1.2 f 0.9, respectively. The degeneracy of the Q state (IE, in D4h symmetry) is lowered by Jahn-Teller and crystal-field effects, with the splitting of the Q(0,O) band being -30 cm-'. Analysis of the spectra in the Q-band region yields Jahn-Teller parameters YJT = 140 f 4 cm-I, AJT = 1.27 f 0.5, and EJT = 26 f 3 cm-' and suggests that the crystal-field distortion is of the same symmetry as the Jahn-Teller effect and of magnitude 30 f 4 cm-I. Qualitative indications are that Jahn-Teller effects in the B and P (lowest triplet) states are weaker than that in the Q state.

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“…The coherent phases  R t are only considered for the vibrations of the sample molecules, whose susceptibility 3 R is resonantly enhanced. The complexity of the electronic susceptibility is introduced as 3 …”

Section: Fitting Of the Resonant Cars Spectramentioning

confidence: 99%

“…The assignment is consistent with (i) a set of assignments reported for Zn-OEP modes when the porphyrin is excited near the Soret band, 2,3 (ii) a normalcoordinate analysis in modified and substituted Ni-OEPs 5,9 and (iii) other CARS experimental data on various metallooctaethylporphyrins. 7 -10,17 -19,21 Resonance Raman studies of Zn-OEP, with an excitation wavelength of 436 2 or 450 nm, 3 have provided detailed information on totally symmetric A 1g skeletal modes of the porphyrin. The non-totally symmetric (mainly B 1g ) modes have been resolved only poorly, because of the lack of resonance enhancement in the violet range of wavelengths.…”

Section: Vibrational Assignment In Zn-oepmentioning

confidence: 99%

“…Alternative methods based on non-coherent Raman spectroscopy (SR) have yielded information on the totally symmetric vibrational (A 1g ) modes. These modes can readily be observed when an excitation wavelength of 436 1,2 or 450 nm, 3 near the Soret absorption band, was used. The dispersion of Raman bands of cyclic tetrapyrroles (heme groups and other porphyrins) depends strongly on the excitation wavelength.…”

Section: Introductionmentioning

confidence: 99%

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Vibrational bands of luminescent zinc(II)‐octaethylporphyrin using a polarization‐sensitive ‘microscopic’ multiplex CARS technique

Otto

Voroshilov

Kruglik

et al. 2001

J Raman Spectroscopy

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Polarization-sensitive, multiplex coherent anti-Stokes Raman scattering (ps-MCARS) has been used to detect the vibrational bands of the highly luminescent zinc(II)-octaethylporphyrin (Zn-OEP). We show here that ps-MCARS can be used to measure the vibrational bands under resonant conditions. Polarization-sensitive CARS further helps to resolve composite and overlapping Raman bands on the basis of variations in vibrational symmetry. This paper also exemplifies the advantages of multiplex CARS (MCARS) spectroscopy carried out under tight focusing conditions as proposed earlier. We demonstrate that a 'microscopic' CARS focusing and collection system in combination with the multiplex technique allows a reduction in the amount of sample and a shortening of the measurement time. We analyse the relationship between the coherent vibrational phases and the symmetry of the different vibrational band of Zn-OEP skeletal modes. The values of the coherent vibrational phases are similar for vibrational bands with the same symmetry.

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Picosecond Time-Resolved Resonance Raman Scattering from Zinc(II) Octaethylporphyrin

Cited by 19 publications

References 0 publications

Resonance Raman characterization of the triplet state of zinc tetraphenylchlorin

Resonance Raman characterization of the triplet state of zinc tetraphenylchlorin

Magnetooptical Spectroscopy of Zinc Octaethylporphyrin in an Argon Matrix

Vibrational bands of luminescent zinc(II)‐octaethylporphyrin using a polarization‐sensitive ‘microscopic’ multiplex CARS technique

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