Syntheses and Optical Limiting Characterizations of a Series of Porphyrin-Buckminsterfullerene Dyads
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Mat. Res. Soc. Symp. Proc. Vol. 597 © 2000 Materials Research Society
o-phenylene bridge. Photoinduced electron transfer will be employed as a means to generate the C60- anion in the dyads. The optical limiting responses of the charge-separated species could then be investigated. The electron-donating properties of the porphyrin moieties in the dyads 12PorphyC 60 , Vall2PorphyC 60 and CF 3 12PorphyC 60 were systematically varied via chemical modification. Thus, the ease of electron transfer from the porphyrin to the C60 moiety can be controlled by varying the electron-richness of the porphyrin moieties. Results from steady-state UV-vis absorption and fluorescence spectroscopies, cyclic voltammetry and optical limiting measurements performed on the dyads and their respective model compounds will be presented.
Porphyrin-C60 Dyads
Model Porphyrin Compounds
R R
R
R= TTP
•
CF 3TPP CF 3--ZnTTP
M=
Me-@ - H2
VaITPP
Me---/
/
R
R= 12Porphy
R=
M=
Me \
H2
12PorphyC6o
-
H2
Vail2PorphyC 60
0/
H2
CF 312PorphyC 60 CF3
Me -0-
Zn
Zn12PorphyC6o
H2
Vall2Porphy
H2
CF 312Porphy CF 3
Zn
Znl2Porphy
Me -0/
H2
•
H2
0/
Me--
Model C60 Compounds
N
C60
NMeC6o
Figure 1. Structures of the porphyrin-C60 dyads and their model compounds.
426
M=
H2 Zn
EXPERIMENTAL Room temperature UV-vis absorption spectra were measured on a Hewlett Packard 8543 spectrometer. Steady-state fluorescence measurements were made on an Instruments S.A. (U.K.) Ltd FL3-21 fluorometer at room temperature. Cyclic voltammetric studies at room temperature were performed on an Eco Chemie PGSTAT20 potentiostat/galvanostat in a nitrogen-filled Vacuum Atmosphere Co. dry box (02 < 5 ppm, H2 0 < 10 ppm). CH 2CI 2 was distilled from P20 5 under nitrogen and n-Bu4 PF 6 was dried in vacuo at 80'C prior to use. The electrochemical cell consisted of platinum working and counter electrodes and a silver wire as a reference electrode. The supporting electrolyte was n-Bu 4PF 6 (0.1 M) in CH 2C12 and the Fc/Fc+ redox couple was used as internal reference standard. Optical limiting measurements were performed at 532 nm using either 3-ns or 15-ns pulse widths. Measurements were performed in the single shot mode on solutions with linear transmittances of -40 or 50%. The input energy ranged from 0.004 - 600 WuJ.No signs of damage were observed in the samples even after irradiation at the maximum beam energy. RESULTS AND DISCUSSION Syntheses and Structural Characterizations of Porphyrin-C 60 Dyads Figure 2 illustrates the synthetic route of the porphyrin-C 60 dyads. The porphyrin precursor was synthesized using a mixed Lindsey condensation [23,24]. This is followed by a 1,3-dipolar azomethine ylide cycloaddition [25] to yield the porphyrin-C 60 dyad. The identities of the porphyrin-C 60 dyads were verified by UV-vis absorption spectroscopy, mass spectrometry, and one- and two-dimensional nuclear magnetic resonance (NMR) spectroscopies.
R
s N
1. cat. BF 3 .OEt2, CHCI r.t.
2. DDQ, r.t.
+2RCHO+
N
N
R
H
H CgoN
N
R
H\ /'I 'OH
toluene, refl
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