A theoretical study of the electronic structure and spectra of metalloporphine cations

Edwards, W. Daniel; Zerner, Michael C.

doi:10.1139/v85-296

Cited by 37 publications

(23 citation statements)

References 26 publications

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“…The absorption spectra of the oxidized complexes appear to be a superposition of the spectra of the neutral and cationic species of the different porphyrin units. This observation is consistent with weak interactions between the constituent porphyrins (as also indicated by the electrochemical studies). − …”

Section: Resultssupporting

confidence: 88%

Effects of Orbital Ordering on Electronic Communication in Multiporphyrin Arrays

et al. 1997

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The rational design of molecular photonic devices requires a thorough understanding of all factors affecting electronic communication among the various constituents. To explore how electronic factors mediate both excited- and ground-state electronic communication in multiporphyrin arrays, we have conducted a detailed static spectroscopic (absorption, fluorescence, resonance Raman, electron paramagnetic resonance), time-resolved spectroscopic (absorption, fluorescence), and electrochemical (cyclic and square-wave voltammetry, coulometry) study of tetraarylporphyrin dimers. The complexes investigated include both zinc-free base (ZnFb) and bis-Zn dimers in which the porphyrin constituents are linked via diphenylethyne groups at the meso positions. Comparison of dimeric arrays containing pentafluorophenyl groups at all nonlinking meso positions (F30ZnFbU and F30Zn2U) with nonfluorinated analogs (ZnFbU and Zn2U) directly probes the effects of electronic factors on intradimer communication. The major findings of the study are as follows: (1) Energy transfer from the photoexcited Zn porphyrin to the Fb porphyrin is the predominant excited-state reaction in F30ZnFbU, as is also the case for ZnFbU. Energy transfer primarily proceeds via a through-bond process mediated by the diarylethyne linker. Remarkably, the energy-transfer rate is 10 times slower in F30ZnFbU ((240 ps)-1) than in ZnFbU ((24 ps)-1), despite the fact that each has the same diphenylethyne linker. The attenuated energy-transfer rate in the former dimer is attributed to reduced Q-excited-state electronic coupling between the Zn and Fb porphyrins. (2) The rate of hole/electron hopping in the monooxidized bis-Zn complex, [F30Zn2U]+, is ∼10-fold slower than that for [Zn2U]+. The slower hole/electron hopping rate in the former dimer reflects strongly attenuated ground-state electronic coupling. The large attenuation in excited- and ground-state electronic communication observed for the fluorine-containing dimers is attributed to a diminution in the electron-exchange matrix elements that stems from stabilization of the a2u porphyrin orbital combined with changes in the electron-density distribution in this orbital. Stabilization of the porphyrin a2u orbital results in a switch in the HOMO from a2u in ZnFbU to a1u in F30ZnFbU. This orbital reversal diminishes the electron density at the peripheral positions where the linker is appended. Collectively, our studies clarify the origin of the different energy-transfer rates observed among various multiporphyrin arrays and exemplify the interconnected critical roles of a1u/a2u orbital ordering and linker position in the design of efficient molecular photonic devices.

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Section: Resultssupporting

confidence: 88%

Effects of Orbital Ordering on Electronic Communication in Multiporphyrin Arrays

et al. 1997

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“…The absorption spectra of the oxidized complexes appear to be a superposition of neutral and cationic species. This observation and the results of the electrochemical studies are consistent with weak interactions between the constituent porphyrins. − …”

Section: Resultssupporting

confidence: 82%

Synthesis and Properties of Star-Shaped Multiporphyrin−Phthalocyanine Light-Harvesting Arrays

Diers

Seth

et al. 1999

J. Org. Chem.

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Light-harvesting arrays containing four porphyrins covalently linked to a phthalocyanine in a star-shaped architecture have been synthesized. Cyclotetramerization of an ethyne-linked porphyrin−phthalonitrile in 1-pentanol in the presence of MgCl2 and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) afforded the all-magnesium porphyrin−phthalocyanine pentad in 45% yield. Similar reaction using Zn(OAc)2·2H2O afforded the all-zinc porphyrin−phthalocyanine pentad in 15% yield. Arrays with different metals (free base, Mg, Zn) in the porphyrin and phthalocyanine macrocycles have been prepared by selective demetalation and metalation steps. This approach provides rapid and convergent access to multiporphyrin−phthalocyanine arrays in diverse metalation states. The arrays are reasonably soluble in organic solvents such as toluene, THF, and CH2Cl2. The arrays exhibit strong absorption in the blue and red regions. Time-resolved and static optical measurements indicate that intramolecular singlet-excited-state energy transfer from the porphyrin to the phthalocyanine moiety is extremely rapid (picoseconds) and efficient. Ground-state electronic communication among the porphyrins is indicated by rapid hole/electron hopping among the metalloporphyrins in the arrays as detected by EPR measurements on the singly oxidized pentads. These physical measurements indicate that the porphyrin−phthalocyanine pentads possess favorable characteristics for light harvesting and other photonics applications.

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“…The one centered at 322 nm corresponds to the N band of Edwards and coworkers.8. 26 The other, at -252 nm, has energy (-39 700 cm-I) and relative intensity close to those predicted for the L transition of the porphin d i a n i~n~~-~~ and is assigned accordingly. The fact that it has not been observed previously in solution or gasphase spectra of ZnOEP is probably a consequence of large bandwidths and spectral overlap with the N and M bands.…”

Section: Resultssupporting

confidence: 59%

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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A theoretical study of the electronic structure and spectra of metalloporphine cations

Cited by 37 publications

References 26 publications

Effects of Orbital Ordering on Electronic Communication in Multiporphyrin Arrays

Effects of Orbital Ordering on Electronic Communication in Multiporphyrin Arrays

Synthesis and Properties of Star-Shaped Multiporphyrin−Phthalocyanine Light-Harvesting Arrays

Magnetooptical Spectroscopy of Zinc Octaethylporphyrin in an Argon Matrix

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