Strongly Coupled Oxasmaragdyrin–BF₂ Chelated Dipyrrin Dyads: Syntheses, X‐ray Structure, Ground‐ and Excited‐State Charge‐Transfer Interactions

Abstract

Oxasmaragdyrin (osm), a 22-π electron aromatic macrocycle containing four pyrroles and a furan ring connected by three methine bridges and two direct bonds is shown to be an excellent electron donor-sensitizer exhibiting adequate spectral and redox properties. Further, this novel heterocyclic macromolecule has been utilized in building donor-acceptor systems involving BF -chelated dipyrromethenes (BODIPYs). The osm-BODIPY dyads were fully characterized by optical, electrochemical, computational, and X-ray diffraction studies. Due to close proximity and electronic structure of the donor and acceptor entities, strong intramolecular charge-transfer interactions in these dyads was witnessed and was supported by computational studies. Solvent-polarity-dependent rapid charge separation and charge recombination in these dyads is witnessed from photochemical studies involving time-resolved emission and femtosecond transient absorption studies. The present studies bring out the importance of oxasmaragdyrin as an electron donor in light-energy-harvesting artificial photosynthesis model systems.

Ultrafast Charge‐Separation in Triphenylamine‐BODIPY‐Derived Triads Carrying Centrally Positioned, Highly Electron‐Deficient, Dicyanoquinodimethane or Tetracyanobutadiene Electron‐Acceptors

“…These results clearly indicate that the electronic absorption of the TPA‐substituted BODIPYs is a function of the acceptor strength. As expected for charge transfer bands, changing the solvent to the more polar benzonitrile caused additional red‐shifting of the charge transfer band to 662 nm, as shown in Figure a …”

“…As expected for charget ransfer bands, changing the solvent to the more polar benzonitrile caused additional red-shifting of the charge transfer band to 662 nm, as shown in Figure 2a. [21] As shown in Figure 2b(i), the steady-state fluorescences pectrum of BODIPY 1 in toluene was found to be located at 612 nm. Thisp eak was significantly red-shifted from the fluorescence of pristineB ODIPY derivatives, which are known to emit in the 520 nm range.…”

Assessment of BODIPY–Oxasmaragdyrin Dyads for Dye-Sensitized Solar Cells: Aromaticity, Photosensitization Capability, and Charge Transport

“…Recent studies have shown the importance of oxasmaragdyrin sensitizer as a compelling material for light-energy-harvesting applications. − For instance, boryl oxasmaragdyrin offers many advantages, such as simpler synthesis and purification processes, low cost, and moisture stability. Besides, very recently, it has been found that such aromatic core-modified expanded porphyrins are efficient hole-transporting materials (HTMs) for perovskite solar cells (PSCs) as they retard charge recombination and transport the photogenerated hole to the counter electrode …”

“…On the other hand, boron–dipyrromethene units (BODIPY) are also molecular systems commonly used for efficient light capture, mainly in the far visible or UV region of the electromagnetic spectrum. The photophysical properties of BODIPY and derivatives have been previously studied by Jacquemin’s and Russo’s groups. − The coupling of oxasmaragdyrins with BODIPY through different types of linkers could also enhance the photosensitization properties of the porphyrin derivatives. , Experimentally, the effect of spacers or bridges between chromophores has been studied. Among the bridges that have shown the best results in electronic transfer are those containing acene, thiophene, and phenylethynyl groups.…”

“…27−32 The coupling of oxasmaragdyrins with BODIPY through different types of linkers could also enhance the photosensitization properties of the porphyrin derivatives. 23,33 Experimentally, the effect of spacers or bridges between chromophores has been studied. Among the bridges that have shown the best results in electronic transfer are those containing acene, 34 thiophene, 35 and phenylethynyl 36 groups.…”