Control over Photoinduced Energy and Electron Transfer in Supramolecular Polyads of Covalently linked azaBODIPY-Bisporphyrin ‘Molecular Clip’ Hosting Fullerene

Abstract

A 'molecular clip' featuring a near-IR emitting fluorophore, BF 2 -chelated tetraarylazadipyrromethane (aza-BODIPY) covalently linked to two porphyrins (MP, M = 2H or Zn) has been newly synthesized to host a threedimensional electron acceptor fullerene via a 'two-point' metal−ligand axial coordination. Efficient singlet−singlet excitation transfer from 1 ZnP* to aza-BODIPY was witnessed in the dyad and triad in nonpolar and less polar solvents, such as toluene and o-dichlorobenzene, however, in polar solvents, additional electron transfer occurred along with energy transfer. A supramolecular tetrad was formed by assembling bis-pyridine functionalized fullerene via a 'two-point' metal−ligand axial coordination, and the resulted complex was characterized by optical absorption and emission, computational, and electrochemical methods. Electron transfer from photoexcited zinc porphyrin to C 60 is witnessed in the supramolecular tetrad from the femtosecond transient absorption spectral studies. Further, the supramolecular polyads (triad or tetrad) were utilized to build photoelectrochemical cells to check their ability to convert light into electricity by fabricating FTO/SnO 2 /polyad electrodes. The presence of azaBODIPY and fullerene entities of the tetrad improved the overall light energy conversion efficiency. An incident photon-to-current conversion efficiency of up to 17% has been achieved for the tetrad modified electrode.

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

“…Bidentate fullerene based axial ligation: To mimic the energy and electron transfer events of natural photosynthetic processes, azaBODIPY (ADP) was covalently linked with two porphyrins via an ester linkage to generate a spatial arrangement featuring a molecular clip to host C 60 via metal-ligand axial coordination [115]. Here, C 60 was intentionally functionalized with two pyridine moieties to coordinate to both zinc porphyrins of the host system as shown In another study, to investigate photoinduced energy transfer followed by an electron transfer processes, a dyad possessing ZnP and ZnPc covalently linked by an ester linkage was designed and synthesized [116].…”

Azadipyrromethenes: from traditional dye chemistry to leading edge applications

“…The bis-phenolic substituted derivative 29h has also been elegantly employed as starting point for the synthesis of several dyad and triad donor acceptor materials, by coupling with BODIPY 84,85 , Zntetraarylporphyrin 85,86 , Zn-phthalocyanine 87 , and subphthalocyanines. 88 Complementary to synthetic routes, extensive time-dependent density functional theory (TD-DFT) calculations have been utilised to gain understanding of the structural effects on electronic structure and predict the important photophysical characteristics of this chromophore class.…”

Energy transfer in supramolecular materials for new applications in photonics and electronics

“…60 Sequential energy-electron transfer was also observed when the phthalocyanine-porphyrin dyad was non-covalently attached to a fullerene by axial metal ion coordination, 61 and in an analogous system using an additional bodipy fluorophore. 62 Control over energy vs electron transfer processes in the well-studied porphyrin-fullerene architectures can generally be obtained by varying the solvent polarity, with non-polar environments favoring energy transfer whereas more polar solvents will accelerate electron transfer by stabilizing the ensuing radical ion pair that is generated. Threepoint H-B was used by Rotello and co-workers 63 to assemble fullerenes on the periphery of suitable modified quantum dots.…”