Picosecond Dynamics of Energy Transfer in Porphyrin−Sapphyrin Noncovalent Assemblies

Abstract

The picosecond dynamics of noncovalent ensembles for energy transfer based on anion chelation are reported. The photoactive noncovalent complexes are assembled via salt-bridge formation between carboxyl-containing porphyrin photodonors and a monoprotonated pentapyrrolic sapphyrin acceptor. These complexes are formed with a K a of ca. 103 M-1 upon mixing the receptor and substrate in their respective free-acid and free-base forms in CD2Cl2 (as judged by 1H NMR spectroscopic means). Upon irradiation at 417 nm, singlet−singlet energy transfer from the porphyrin to the sapphyrin subunit takes place readily with energy transfer dynamics that are consistent with a Förster-type mechanism. The title systems thus appear to be prototypic of a new kind of noncovalent energy transfer modeling that is predicated on the use of anion chelation.

Synthesis and Studies of Covalently Linked Porphyrin‐Expanded Heteroporphyrin Dyads

“…The smaragdyrin building block, 19-(4-iodophenyl)-5,10-ditolyl-25-oxasmaragdyrin (4) was synthesized by condensing one equivalent of meso-(iodophenyl)dipyrromethane (6) with one equivalent of 16-oxatripyrrane [12] (10) in dichloromethane in the presence of 0.1 equiv. of trifluoroacetic acid at room temperature under a nitrogen atmosphere, followed by oxidation with DDQ in air.…”

“…Hence, an assembly of expanded macrocycle and normal porphyrin/corrole would offer an opportunity of creating interesting electronic interactions between two macrocycles both in the ground and excited states; such interactions may be tuned further by appropriate metalation either at one or at both macrocycles. Interestingly, there are very few reports on covalently or noncovalently linked, expanded porphyrin-porphyrin dyads [6] or higher oligomers. Sessler and co-workers [6a,6b] created a noncovalent por-solvents and were characterized by various spectroscopic techniques.…”

Electronic Conduction in Photoactive Metallo‐wires

“…This field was developed primarily by Sessler [155] who has produced a series of porphyrin-based systems that display intraassembly energy [156][157][158][159][160] or electron transfer [161,162]. In most cases it is difficult to conclude if electron transfer proceeds through the hydrogen bonds, as opposed to diffusional contact between the main reactants, but in certain semirigid arrays this seems to be the case.…”

Synthesis of Covalently Linked Porphyrin Heterodimers with Potential Use in the Solar Energy Conversion Devices

“…nature of spacers, distance and orientation of donor with respect to acceptor) have been synthesized and their photophysical properties have been described in literature. [3,[21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] Irradiation of a donor pigment within a porphyrin dimer is followed by an effective energy transfer and, in some cases, a direct transformation of sunlight energy to the charge-separated state by means of electron transfer.…”

“…That allows a selective excitation of one porphyrin moiety of dyad and provides a driving force for energy or electron transfer after irradiation. Examples of directional energy transfer between two different macrocycles include: a tetraarylporphyrin covalently linked to a pyropheophorbide, [22] a porphyrin-sapphyrin heterodimer which is held together by hydrogen bonds, [23] covalently linked chlorophyll-porphyrin [24] and zinc porphyrin-pheophorbide [25] heterodimers, porphyrin-chlorin dyads with aryl spacer [26] and ether linkage between macrocycles, [27] porphyrin-phthalocyanine dyads, [28,29] several heteroporphyrin dyads with amide linkage [30,31] and phenylene bridging group, [32] diporphyrins containing a normal porphyrin and a thiaporphyrin cores, [33] phenylethyne-linked dyads in which the ethyne-substituted porphyrin serves as the acceptor while the phenyl-substituted porphyrin serves as the donor [34] and recently described "clicked" dimers of unsymmetrically substituted tetraphenylporphyrins. [35] Unsymmetrical porphyrin dimers are not only useful models for mimicry of photosynthetic energy and electron transfer but its have a potential application in the spectral sensitization of semiconductor solar cells.…”