Photoinduced Electron and Energy Transfer in a Molecular Triad Featuring a Fullerene Redox Mediator

Abstract

In order to investigate the possibility of a fullerene acting as an electron and/or singlet energy relay between a donor chromophore and an acceptor, a triad consisting of a fullerene (C60) covalently linked to both a porphyrin energy and electron donor (P) and a β-tetracyanoporphyrin energy and electron acceptor (CyP) was synthesized. Steady state and time-resolved spectroscopic investigations show that the porphyrin first excited singlet state donates singlet excitation and an electron to the fullerene and also donates singlet excitation to the CyP. All three processes differ in rate constant by factors of ≤1.3, and all are much faster than the decay of (1)P-C60-CyP by unichromophoric processes. The fullerene excited state accepts an electron from P and donates singlet excitation energy to CyP. The P(•+)-C60(•-)-CyP charge-separated state transfers an electron to CyP to produce a final P(•+)-C60-CyP(•-) state. The same state is formed from P-C60-(1)CyP. Overall, the final charge-separated state is formed with a quantum yield of 85% in benzonitrile, and has a lifetime of 350 ps. Rate constants for formation and quantum yields of all intermediate states were estimated from results for the triad and several model compounds. Interestingly, the intermediate P(•+)-C60(•-)-CyP charge-separated state has a lifetime of 660 ps. It is longer lived than the final state in spite of stronger coupling of the radical ions. This is ascribed to the fact that recombination lies far into the inverted region of the Marcus rate constant vs thermodynamic driving force relationship.

Photoinduced Electron Transfer from ZrOCo Binuclear Light Absorber to Pyridine Elucidated by Transient Optical and Infrared Spectroscopy

“…fluorescence or transient absorption). [78][79][80] Spectra suggest that our system functions most closely according to this latter type, Co→Zr→pyr. FT-IR spectra reveal two types of ZrOCo sites, namely those with pyridine interacting with the Co center and sites that feature pyridine interacting with the Zr center.…”

Fully Conjugated Pyrene–BODIPY and Pyrene–BODIPY–Ferrocene Dyads and Triads: Synthesis, Characterization, and Selective Noncovalent Interactions with Nanocarbon Materials

“…Design of new chromophores that are capable of harvesting sunlight in the low-energy visible and near-infrared (NIR) spectral envelopes attracted a lot of attention in recent decades because of the potential use of such systems in organic- and dye-sensitized solar cells. − In addition, the ability to facilitate relatively strong noncovalent interactions between such chromophores and nanocarbon-based electron-accepting materials (fullerenes, nanotubes, and graphene) is thought to be advantageous in the processing of high-efficiency organic bulk heterojunction solar cells. − To achieve this goal, many porphyrins, − subphthalocyanines, − and boron-dipyrromethenes (BODIPYs) were functionalized with a variety of electron-donating groups that improve donor–acceptor (D–A) interactions between extended π-systems. Alternatively, the introduction of the polyaromatic fragments that are either conjugated or not conjugated into chromophores’ π-system can also improve noncovalent interactions in these D–A assemblies. − Covalently bound pyrene was shown to facilitate noncovalent interactions with carbon nanotubes and graphene. − It has also been shown that when pyrene fragments are decoupled from the chromophores’ π-system, this extended aromatic group can facilitate an unwanted pyrene-to-chromophore electron-transfer process as well as the formation of a chromophore-centered triplet state. − We have recently demonstrat...…”

Directly Linked Zinc Phthalocyanine–Perylenediimide Dyads and a Triad for Ultrafast Charge Separation

“…In all the three conjugates, the first DAS, revealing negative amplitudes (rise component) at positions where both cation and anion radical signals were expected, were within a few picoseconds, suggesting formation of a charge‐separated state at this timescale. The second component with positive amplitude (decay component) at wavelengths corresponding to the charge‐separated state species was attributed to the lifetime of the charge‐separated state . At higher timescales, a third and a fourth component were seen.…”

“…The second component with positive amplitude (decay component) at wavelengthsc orresponding to the charge-separated state speciesw as attributed to the lifetimeo ft he charge-separated state. [17] At higher timescales, at hird and af ourth component were seen. The third component has ap ositive peak at 830 nm corresponding to that of 3 ZnPc* whereas the fourth component was featureless.…”