A series of meso-substituted with aromatic (=tolyl, pyrenyl,
fluorenyl, naphthyl, and triphenyla... more A series of meso-substituted with aromatic (=tolyl, pyrenyl,
fluorenyl, naphthyl, and triphenylamine) substituents, platinum
(Pt), and palladium (Pd) porphyrins have been synthesized and
characterized by spectroscopic and single-crystal X-ray diffraction studies to probe structure-reactivity aspects on the electrochemical redox potentials, and phosphorescence quantum
yields and lifetimes. In the X-ray structures, the aromatic mesosubstituents were rotated to some extent from the planarity of
the porphyrin ring to minimize steric hindrance. Both Pt and Pd
porphyrins revealed higher electrochemical redox gaps as
compared to their free-base porphyrin analogs as a result of the
harder oxidation and reduction processes. The ability of both Pt
and Pd porphyrins to generate singlet oxygen was probed by
monitoring the photoluminescence of 1
O2 at 1270 nm. Higher
quantum yields for both triplet sensitizers compared to their
free-base analogs were witnessed. Singlet oxygen quantum
yields close to unity were possible to achieve in the case of Pt
and Pd porphyrins bearing triphenylamine substituents at the
meso-position. The present study brings out the importance of
different meso-substituents on the triplet porphyrin sensitizers
in governing singlet oxygen quantum yields; a key property of
photosensitizers needed for photodynamic therapy, chemical
synthesis, and other pertinent applications.
Two types of cobalt porphyrins, viz., meso-tetrakis(tolylporphyrinato)cobalt(II), (TTP)Co (1), an... more Two types of cobalt porphyrins, viz., meso-tetrakis(tolylporphyrinato)cobalt(II), (TTP)Co (1), and meso-tetrakis(triphenylamino porphyrinato)cobalt(II), [(TPA) 4 P]Co, (2) were self-assembled via metal-ligand axial coordination of phenyl imidazole functionalized fulleropyrrolidine, ImC 60 to form a new series of donor-acceptor constructs. A 1:2 complex formation with ImC 60 was established in the case of (TTP)Co while for [(TPA) 4 P]Co only a 1:1 complex was possible to positively identify. The binding constants K 1 and K 2 for step-wise addition of ImC 60 to (TTP)Co were found to be 1.07 × 10 5 and 3.20 × 10 4 M-1 , respectively. For [(TPA) 4 P]Co:ImC 60 , the measured K 1 values was found to be 6.48 × 10 4 M-1 , slightly smaller than that observed for (TTP)Co. Although both cobalt porphyrins were non-fluorescent, they were able to quench the fluorescence of ImC 60 indicating occurrence of excited state events in the supramolecular donor-acceptor complexes. Electrochemistry coupled with spectroelectrochemistry, revealed the formation of cobalt(III) porphyrin cation instead of a cobalt(II) porphyrin radical cation, as the main product, during oxidation of phenyl imidazole coordinated cobalt porphyrin. With the help of computational and electrochemical results, an energy level diagram was constructed to witness excited state photo-events. Competitive energy and electron transfer from excited CoP to coordinated ImC 60 , and electron transfer from Im 1 C 60 * to cobalt(II) porphyrin resulting into the formation of PCo III :ImC 60 •charge separated state was possible to envision from the energy diagram. Finally, using femtosecond transient absorption spectroscopy and data analysis by Glotaran, it was possible to establish sequential occurrence of energy transfer and charge separation processes. The lifetime of the final charge separated state was ~ 2 ns. A slightly better charge stabilization was observed in the case of [(TPA) 4 P]Co:ImC 60 due to the presence of electron rich, peripheral triphenylamine substituents on the cobalt porphyrin.
The formation of a high-energy, long-lived radical ion-pair by electron transfer exclusively from... more The formation of a high-energy, long-lived radical ion-pair by electron transfer exclusively from the triplet excited state, is demonstrated in a newly synthesized platinum porphyrin-fullerene dyad, in which the porphyrin ring is modified with three electron rich triphenylamine entities. The spin selectivity of the electron transfer leading to the formation of the radical ion-pair is demonstrated using time-resolved optical and EPR spectroscopic techniques.
A series of meso-substituted with aromatic (= tolyl, pyrenyl, fluorenyl, naphthyl, and triphenyla... more A series of meso-substituted with aromatic (= tolyl, pyrenyl, fluorenyl, naphthyl, and triphenylamine) substituents, platinum (Pt), and palladium (Pd) porphyrins have been synthesized and characterized by spectroscopic and single-crystal X-ray diffraction studies to probe structure-reactivity aspects on the electrochemical redox potentials, and phosphorescence quantum yields and lifetimes. In the X-ray structures, the aromatic mesosubstituents were rotated to some extent from the planarity of the porphyrin ring to minimize steric hindrance. Both Pt and Pd porphyrins revealed higher electrochemical redox gaps as compared to their free-base porphyrin analogs as a result of the harder oxidation and reduction processes. The ability of both Pt and Pd porphyrins to generate singlet oxygen was probed by monitoring the photoluminescence of 1 O 2 at 1270 nm. Higher quantum yields for both triplet sensitizers compared to their free-base analogs were witnessed. Singlet oxygen quantum yields close to unity were possible to achieve in the case of Pt and Pd porphyrins bearing triphenylamine substituents at the meso-position. The present study brings out the importance of different meso-substituents on the triplet porphyrin sensitizers in governing singlet oxygen quantum yields; a key property of photosensitizers needed for photodynamic therapy, chemical synthesis, and other pertinent applications.
Radical ion-pair energy as high as 1.48 eV with lifetime as much as ∼1 μs, exclusively from the t... more Radical ion-pair energy as high as 1.48 eV with lifetime as much as ∼1 μs, exclusively from the triplet excited state of a photosensitizer, is established in a novel donor–acceptor conjugate.
Two types of cobalt porphyrins, viz., meso-tetrakis(tolylporphyrinato)cobalt(II), (TTP)Co (1), an... more Two types of cobalt porphyrins, viz., meso-tetrakis(tolylporphyrinato)cobalt(II), (TTP)Co (1), and meso-tetrakis(triphenylamino porphyrinato)cobalt(II), [(TPA)4P]Co, (2) were self-assembled via metal-ligand axial coordination of phenyl imidazole functionalized fulleropyrrolidine, ImC[Formula: see text] to form a new series of donor–acceptor constructs. A 1:2 complex formation with ImC[Formula: see text] was established in the case of (TTP)Co while for [(TPA)4P]Co only a 1:1 complex was possible to positively identify. The binding constants [Formula: see text] and [Formula: see text] for step-wise addition of ImC[Formula: see text] to (TTP)Co were found to be 1.07 × 105 and 3.20 × 104 M[Formula: see text], respectively. For [(TPA)4P]Co:ImC[Formula: see text], the measured [Formula: see text] values was found to be 6.48 × 104 M[Formula: see text], slightly smaller than that observed for (TTP)Co. Although both cobalt porphyrins were non-fluorescent, they were able to quench the fluores...
A series of meso-substituted with aromatic (=tolyl, pyrenyl,
fluorenyl, naphthyl, and triphenyla... more A series of meso-substituted with aromatic (=tolyl, pyrenyl,
fluorenyl, naphthyl, and triphenylamine) substituents, platinum
(Pt), and palladium (Pd) porphyrins have been synthesized and
characterized by spectroscopic and single-crystal X-ray diffraction studies to probe structure-reactivity aspects on the electrochemical redox potentials, and phosphorescence quantum
yields and lifetimes. In the X-ray structures, the aromatic mesosubstituents were rotated to some extent from the planarity of
the porphyrin ring to minimize steric hindrance. Both Pt and Pd
porphyrins revealed higher electrochemical redox gaps as
compared to their free-base porphyrin analogs as a result of the
harder oxidation and reduction processes. The ability of both Pt
and Pd porphyrins to generate singlet oxygen was probed by
monitoring the photoluminescence of 1
O2 at 1270 nm. Higher
quantum yields for both triplet sensitizers compared to their
free-base analogs were witnessed. Singlet oxygen quantum
yields close to unity were possible to achieve in the case of Pt
and Pd porphyrins bearing triphenylamine substituents at the
meso-position. The present study brings out the importance of
different meso-substituents on the triplet porphyrin sensitizers
in governing singlet oxygen quantum yields; a key property of
photosensitizers needed for photodynamic therapy, chemical
synthesis, and other pertinent applications.
Two types of cobalt porphyrins, viz., meso-tetrakis(tolylporphyrinato)cobalt(II), (TTP)Co (1), an... more Two types of cobalt porphyrins, viz., meso-tetrakis(tolylporphyrinato)cobalt(II), (TTP)Co (1), and meso-tetrakis(triphenylamino porphyrinato)cobalt(II), [(TPA) 4 P]Co, (2) were self-assembled via metal-ligand axial coordination of phenyl imidazole functionalized fulleropyrrolidine, ImC 60 to form a new series of donor-acceptor constructs. A 1:2 complex formation with ImC 60 was established in the case of (TTP)Co while for [(TPA) 4 P]Co only a 1:1 complex was possible to positively identify. The binding constants K 1 and K 2 for step-wise addition of ImC 60 to (TTP)Co were found to be 1.07 × 10 5 and 3.20 × 10 4 M-1 , respectively. For [(TPA) 4 P]Co:ImC 60 , the measured K 1 values was found to be 6.48 × 10 4 M-1 , slightly smaller than that observed for (TTP)Co. Although both cobalt porphyrins were non-fluorescent, they were able to quench the fluorescence of ImC 60 indicating occurrence of excited state events in the supramolecular donor-acceptor complexes. Electrochemistry coupled with spectroelectrochemistry, revealed the formation of cobalt(III) porphyrin cation instead of a cobalt(II) porphyrin radical cation, as the main product, during oxidation of phenyl imidazole coordinated cobalt porphyrin. With the help of computational and electrochemical results, an energy level diagram was constructed to witness excited state photo-events. Competitive energy and electron transfer from excited CoP to coordinated ImC 60 , and electron transfer from Im 1 C 60 * to cobalt(II) porphyrin resulting into the formation of PCo III :ImC 60 •charge separated state was possible to envision from the energy diagram. Finally, using femtosecond transient absorption spectroscopy and data analysis by Glotaran, it was possible to establish sequential occurrence of energy transfer and charge separation processes. The lifetime of the final charge separated state was ~ 2 ns. A slightly better charge stabilization was observed in the case of [(TPA) 4 P]Co:ImC 60 due to the presence of electron rich, peripheral triphenylamine substituents on the cobalt porphyrin.
The formation of a high-energy, long-lived radical ion-pair by electron transfer exclusively from... more The formation of a high-energy, long-lived radical ion-pair by electron transfer exclusively from the triplet excited state, is demonstrated in a newly synthesized platinum porphyrin-fullerene dyad, in which the porphyrin ring is modified with three electron rich triphenylamine entities. The spin selectivity of the electron transfer leading to the formation of the radical ion-pair is demonstrated using time-resolved optical and EPR spectroscopic techniques.
A series of meso-substituted with aromatic (= tolyl, pyrenyl, fluorenyl, naphthyl, and triphenyla... more A series of meso-substituted with aromatic (= tolyl, pyrenyl, fluorenyl, naphthyl, and triphenylamine) substituents, platinum (Pt), and palladium (Pd) porphyrins have been synthesized and characterized by spectroscopic and single-crystal X-ray diffraction studies to probe structure-reactivity aspects on the electrochemical redox potentials, and phosphorescence quantum yields and lifetimes. In the X-ray structures, the aromatic mesosubstituents were rotated to some extent from the planarity of the porphyrin ring to minimize steric hindrance. Both Pt and Pd porphyrins revealed higher electrochemical redox gaps as compared to their free-base porphyrin analogs as a result of the harder oxidation and reduction processes. The ability of both Pt and Pd porphyrins to generate singlet oxygen was probed by monitoring the photoluminescence of 1 O 2 at 1270 nm. Higher quantum yields for both triplet sensitizers compared to their free-base analogs were witnessed. Singlet oxygen quantum yields close to unity were possible to achieve in the case of Pt and Pd porphyrins bearing triphenylamine substituents at the meso-position. The present study brings out the importance of different meso-substituents on the triplet porphyrin sensitizers in governing singlet oxygen quantum yields; a key property of photosensitizers needed for photodynamic therapy, chemical synthesis, and other pertinent applications.
Radical ion-pair energy as high as 1.48 eV with lifetime as much as ∼1 μs, exclusively from the t... more Radical ion-pair energy as high as 1.48 eV with lifetime as much as ∼1 μs, exclusively from the triplet excited state of a photosensitizer, is established in a novel donor–acceptor conjugate.
Two types of cobalt porphyrins, viz., meso-tetrakis(tolylporphyrinato)cobalt(II), (TTP)Co (1), an... more Two types of cobalt porphyrins, viz., meso-tetrakis(tolylporphyrinato)cobalt(II), (TTP)Co (1), and meso-tetrakis(triphenylamino porphyrinato)cobalt(II), [(TPA)4P]Co, (2) were self-assembled via metal-ligand axial coordination of phenyl imidazole functionalized fulleropyrrolidine, ImC[Formula: see text] to form a new series of donor–acceptor constructs. A 1:2 complex formation with ImC[Formula: see text] was established in the case of (TTP)Co while for [(TPA)4P]Co only a 1:1 complex was possible to positively identify. The binding constants [Formula: see text] and [Formula: see text] for step-wise addition of ImC[Formula: see text] to (TTP)Co were found to be 1.07 × 105 and 3.20 × 104 M[Formula: see text], respectively. For [(TPA)4P]Co:ImC[Formula: see text], the measured [Formula: see text] values was found to be 6.48 × 104 M[Formula: see text], slightly smaller than that observed for (TTP)Co. Although both cobalt porphyrins were non-fluorescent, they were able to quench the fluores...
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Papers by Dili Subedi
fluorenyl, naphthyl, and triphenylamine) substituents, platinum
(Pt), and palladium (Pd) porphyrins have been synthesized and
characterized by spectroscopic and single-crystal X-ray diffraction studies to probe structure-reactivity aspects on the electrochemical redox potentials, and phosphorescence quantum
yields and lifetimes. In the X-ray structures, the aromatic mesosubstituents were rotated to some extent from the planarity of
the porphyrin ring to minimize steric hindrance. Both Pt and Pd
porphyrins revealed higher electrochemical redox gaps as
compared to their free-base porphyrin analogs as a result of the
harder oxidation and reduction processes. The ability of both Pt
and Pd porphyrins to generate singlet oxygen was probed by
monitoring the photoluminescence of 1
O2 at 1270 nm. Higher
quantum yields for both triplet sensitizers compared to their
free-base analogs were witnessed. Singlet oxygen quantum
yields close to unity were possible to achieve in the case of Pt
and Pd porphyrins bearing triphenylamine substituents at the
meso-position. The present study brings out the importance of
different meso-substituents on the triplet porphyrin sensitizers
in governing singlet oxygen quantum yields; a key property of
photosensitizers needed for photodynamic therapy, chemical
synthesis, and other pertinent applications.
fluorenyl, naphthyl, and triphenylamine) substituents, platinum
(Pt), and palladium (Pd) porphyrins have been synthesized and
characterized by spectroscopic and single-crystal X-ray diffraction studies to probe structure-reactivity aspects on the electrochemical redox potentials, and phosphorescence quantum
yields and lifetimes. In the X-ray structures, the aromatic mesosubstituents were rotated to some extent from the planarity of
the porphyrin ring to minimize steric hindrance. Both Pt and Pd
porphyrins revealed higher electrochemical redox gaps as
compared to their free-base porphyrin analogs as a result of the
harder oxidation and reduction processes. The ability of both Pt
and Pd porphyrins to generate singlet oxygen was probed by
monitoring the photoluminescence of 1
O2 at 1270 nm. Higher
quantum yields for both triplet sensitizers compared to their
free-base analogs were witnessed. Singlet oxygen quantum
yields close to unity were possible to achieve in the case of Pt
and Pd porphyrins bearing triphenylamine substituents at the
meso-position. The present study brings out the importance of
different meso-substituents on the triplet porphyrin sensitizers
in governing singlet oxygen quantum yields; a key property of
photosensitizers needed for photodynamic therapy, chemical
synthesis, and other pertinent applications.