Photochemistry of Free-Base Porphyrin Linked to Methyl Viologen

1992 ◽  
Vol 57 (1) ◽  
pp. 26-32 ◽  
Author(s):  
N. M. Guindy ◽  
F. M. Elzawawy ◽  
D. Y. Sabry
Keyword(s):  
Methyl Viologen ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Phenyl Group ◽  
Laser Flash ◽  
Porphyrin Ring ◽  
Free Base ◽  
Intramolecular Quenching ◽  
Quenching Efficiency ◽  
Triton X

The photochemistry of free-base meso-tetraphenylporphyrin linked to methyl viologen via an alkoxy chain (n = 3) at the ortho, meta or para-position of one meso-phenyl group, in Triton X-100 micellar aqueous solutions is reported. The appended viologen does not quench the porphyrin fluorescence nor its triplet excited state due to the different solubilization of both parts of the molecule in the medium where the porphyrin ring resides in the hydrophobic phase and the alkoxy linker protrudes into the rather diffuse outer phase of detergent oxyethylene units, while the viologen moiety penetrates into the aqueous layer. However, laser flash photolysis measurements show that in the presence of nicotinamide dinucleotide, NADH, the porphyrin ring is reduced to phlorin due to the penetration of NADH into the organic phase. For porphyrin-tetraviologen in which a viologen molecule is linked to each of the porphyrin meso-position via alkoxy chain, fluorescence quenching could be achieved. The values of the quenching efficiency are high (94% in acetonitrile) compared to intramolecular quenching and are dependent upon the solvent viscosity.

Intramolecular photoinduced electron-transfer processes in buta-1,3-diynyl-benzene-linked porphyrin-fullerene dyad

2007 ◽  
Vol 11 (06) ◽  
pp. 397-405 ◽  
Author(s):  
Ken-ichi Yamanaka ◽  
Mamoru Fujitsuka ◽  
Yasuyuki Araki ◽  
Kentaro Tashiro ◽  
Azumi Sato ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Transient Absorption ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Phenyl Group ◽  
Laser Flash ◽  
Ion Pair ◽  
Intramolecular Electron Transfer ◽  
Electron Transfer Processes ◽  
Absorption Measurements

Intramolecular electron-transfer process of porphyrin-fullerene dyad linked by phenyl buta-1,3-diynyl-phenyl unit ( ZnP - sp - C 60) was studied by laser flash photolysis. Picosecond fluorescence lifetime and transient absorption measurements revealed that photoinduced charge-separation takes place via the excited singlet state (1 ZnP *) with the rate constant of (1-2) × 1010 s −1. For the charge recombination, about a half of the radical-ion pair decayed quickly with 2.9 × 109 s −1 as evaluated from picosecond transient absorption measurements, whereas the remaining half was long-lived with slow decay (1.6 × 106 s −1) as estimated from nanosecond transient absorption measurements. The lifetime of the radical-ion pair of ZnP - sp - C 60 was longer than those of directly connected dyads with a buta-1,3-diynyl bridge and buta-1,3-diynyl-phenyl bridge by the insertion of an extra phenyl group in addition to the pyrrodino ring.

Effect of methyl substitution on the intramolecular triplet deactivation of p-methoxy-β-phenylpropiophenone

1991 ◽  
Vol 69 (12) ◽  
pp. 2053-2058 ◽  
Author(s):  
R. Boch ◽  
C. Bohne ◽  
J. C. Netto-Ferreira ◽  
J. C. Scaiano
Keyword(s):  
Charge Transfer ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Nanosecond Laser ◽  
Methyl Substitution ◽  
Intramolecular Quenching ◽  
Conformational Preferences ◽  
Key Words Laser ◽  
Nanosecond Laser Flash Photolysis

The photochemistry of several methyl-substituted p-methoxy-β-phenylpropiophenones (1–5) has been examined by nanosecond laser flash photolysis using 337-nm laser excitation. The ketone triplets decay by intramolecular β-aryl quenching of the carbonyl in a well-known process that is believed to involve charge transfer. Surprisingly, methyl substitution at the β-methylene group, which is not a participant in the deactiviation mechanism, causes a dramatic decrease in the triplet lifetime; the effect is attributed to different conformational preferences in ketones 1–3 and is rationalized on the basis of MMX calculations. Methyl substitution in the β-aryl ring affects the ease of oxidation of this ring and as a result induces changes in the kinetics for intramolecular charge transfer. This conclusion is further supported by electrochemical studies of ketones 1, 4, and 5. Key words: laser flash photolysis, triplet ketones, intramolecular quenching, charge transfer.

Synthesis and photodynamics of diphenylethynyl-bridged porphyrin-quinoidal porphyrin hybrids

2015 ◽  
Vol 19 (01-03) ◽  
pp. 219-232 ◽  
Author(s):  
Shuhei Sakatani ◽  
Takuya Kamimura ◽  
Kei Ohkubo ◽  
Shunichi Fukuzumi ◽  
Fumito Tani
Keyword(s):  
Electron Transfer ◽  
Absorption Spectra ◽  
Zinc Complex ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Electrochemical Analysis ◽  
Coupling Reactions ◽  
Free Base ◽  
Electronic Communications

As new donor–acceptor hybrids for energy and/or electron transfer, zinc complex and free-base of a porphyrin-quinoidal porphyrin dyad linked by a diphenylethynyl bridge were prepared via Sonogashira and subsequent Takahashi coupling reactions. The quinoidal porphyrin units have two dicyanomethylene groups at the opposite meso-positions. The UV-vis absorption spectra of the dyads were almost linear summations of the absorption spectra of each component in comparison with those of the monomeric reference compounds, indicating very weak electronic interactions between the chromophores at the ground state. Both zinc complex and free-base of the reference porphyrin exhibited fluorescence in the range of ca. 600–700 nm upon photoexcitation, while the quinoidal porphyrin monomers showed no fluorescence. The considerable quenching (more than 99%) of the porphyrin fluorescence in the dyads suggested significant electronic communications between the subunits of the excited state. The electrochemical analysis confirmed that the first oxidations of the dyads occur at the porphyrin units and the first reductions take place at the quinoidal porphyrin units. Femtosecond laser flash photolysis of the zinc dyad with photoexcitation at 393 nm showed both ultrafast (<1 ps) energy and electron transfer from the porphyrin unit to the quinoidal porphyrin one, which processes resulted in the quenching of the porphyrin fluorescence. On the other hand, the free-base dyad underwent only energy transfer.

Effect of Aggregation on Bacteriochlorin a Triplet-state Formation: A Laser Flash Photolysis Study¶

2002 ◽  
Vol 76 (5) ◽  
pp. 480 ◽  
Author(s):  
Xavier Damoiseau ◽  
Francis Tfibel ◽  
Maryse Hoebeke ◽  
Marie-Pierre Fontaine-Aupart
Keyword(s):  
Triplet State ◽  
State Formation ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash

A Laser Flash Photolysis and Pulse Radiolysis Study of Primary Photochemical Processes of Flumequine¶

2000 ◽  
Vol 72 (4) ◽  
pp. 451 ◽  
Author(s):  
M. Bazin ◽  
F. Bosca ◽  
M. L. Marin ◽  
M. A. Miranda ◽  
L. K. Patterson ◽  
...  
Keyword(s):  
Pulse Radiolysis ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Photochemical Processes
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