Ultrafast Singlet−Singlet Energy Transfer in Self-Assembled via Metal−Ligand Axial Coordination of Free-Base Porphyrin−Zinc Phthalocyanine and Free-Base Porphyrin−Zinc Naphthalocyanine Dyads

Abstract

Singlet-singlet energy transfer in self-assembled via axial coordination of imidazole-appended (at different positions of one of the meso-phenyl entities) free-base tetraphenylporphyrin, H(2)PIm, to either zinc phthalocyanine, ZnPc, or zinc naphthalocyanine, ZnNc, dyads is investigated in noncoordinating solvents, o-dichlorobenzene and toluene, using both steady-state and time-resolved transient absorption techniques. The newly formed supramolecular dyads were fully characterized by spectroscopic, computational, and electrochemical methods. The binding constants measured from optical absorption spectral data were found to be in the range of 10(4)-10(5) M(-1) for the 1:1 dyads, suggesting fairly stable complex formation. Electrochemical and computational studies suggested that photoinduced electron transfer is a thermodynamically unfavorable process when free-base porphyrin is excited in these dyads. Selective excitation of the donor free-base porphyrin entity was possible in both types of dyads formed by either of the ZnPc or ZnNc energy acceptors. Efficient singlet-singlet energy transfer was observed in these dyads, and the position of imidazole linkage on the free-base porphyrin entity, although flexible, seems to have some control over the overall efficiency of excited energy transfer process. Kinetics of energy transfer was monitored by performing transient absorption measurements using both up-conversion and pump-probe techniques. Such studies revealed ultrafast singlet-singlet energy transfer in the studied dyads with time constants on the order of 2-25 ps depending upon the type of the dyad.

Design and photochemical study of supramolecular donor–acceptor systems assembled via metal–ligand axial coordination

“…al. [101] have designed and studied donor-acceptor dyads using free-base porphyrins as energy donors with zinc phthalocyanine and zinc naphthalocyanine as energy acceptors via metal-ligand axial coordination. To achieve the axial coordination, the free-base porphyrin was functionalized with an imidazole entity at the ortho, meta, or para position of one of the meso-aryl groups to visualize the effect of orientation in energy transfer, as shown in Upon increasing addition of H 2 P(o, m, p)Im to a solution of ZnPc or ZnNc, changes in absorption spectra with isosbestic points were observed in o-dichlorobenzene (DCB) which indicated binding of porphyrins to ZnPc and ZnNc via metal-ligand axial coordination.…”

Synthesis and properties of a heteroleptic µ-nitrido tetrapyrrolic complex

“…In particular those containing the phthalocyanine (Pc) and porphyrin (P) macrocyclic ligands have been recently studied being interesting for the peculiar photoinduced energy transfer processes [1] and being also attractive for their potential use in the field of molecular photovoltaics, artificial photosynthesis and molecular electronic applications. [2][3][4] Several strategies can be used to link each other the two different subunits to obtain a hetero phthalocyanine-porphyrin dyads, resulting in different geometries and properties.…”

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A novel µ-nitrido iron phthalocyanine-iron porphyrin complex has been synthesised and characterised, preliminary DFT calculations have been performed in order to elucidate its UV-vis spectrum.Keywords: Synthesis, phthalocyanine, porphyrin, µ-nitrido dimer.Multi-component organic chromophores having intense visible absorption characteristics covering large part of solar radiation are currently an object of much attention in view of their exploitation as artificial light-harvesting antenna.In particular those containing the phthalocyanine (Pc) and porphyrin (P) macrocyclic ligands have been recently studied being interesting for the peculiar photoinduced energy transfer processes [1] and being also attractive for their potential use in the field of molecular photovoltaics, artificial photosynthesis and molecular electronic applications. [2][3][4] Several strategies can be used to link each other the two different subunits to obtain a hetero phthalocyanine-porphyrin dyads, resulting in different geometries and properties.

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“…It is possible for example to link the different moieties through a conjugated or not spacer between the peripheral positions of one macrocycle [5] toward either the periphery or the central metal of the other macrocycle. [1] Moreover single atom (O, N, C) bridged systems as µ-oxo, µ-nitrido and µ-carbido can also allow a combination, via metal centres, leading to homo/heterometallic and homo/heteroleptic systems.…”

Synthesis of substituted meso-tetraphenylporphyrins in mixed solvent systems

“…They can be used to mimic natural enzyme peroxidase, catalase and heme-containing proteins, 10 which are responsible for molecular binding, 11 oxygen transport 12 and energy transfer. 13 The importance of TPPH 2 synthesis as a methodology has been described in many literatures.…”