Synthesis, Electrochemical and Photochemical Studies on π‐Extended Mono‐β‐Functionalized Porphyrin Dyads

Abstract

A series of π‐conjugated mono‐β‐functionalized donor−acceptor porphyrin dyads (1–4) with various donor groups (phenyl, naphthyl, anthracenyl and pyrenyl) and their metal complexes (M=Zn(1 a–4 a), Cu(1 b–4 b), Co(1 c–4 c) and Ni(1 d–4 d)) were synthesized and characterized by various spectroscopic and electrochemical techniques. A modified one‐step Horner‐Wadsworth‐Emmons reaction was performed on monoformyl porphyrin to get ethenyl‐linked mono‐β‐porphyrin dyads in good to excellent yields (70–90 %). Red‐shifted absorption and emission spectra were observed as compared to unsubstituted pristine tetraphenylporphyrins due to π‐extended donors. Time‐resolved fluorescence studies confirmed the effective intramolecular Förster energy transfer from the donor moiety to the porphyrin core in anthracene‐ and pyrene‐appended porphyrin dyads. DFT and TD‐DFT optimization signified that the orientation of the donor and acceptor plays a vital role in energy transfer as co‐planarity of the donor with the porphyrin core increases the energy transfer efficiency. The distribution of electron density on HOMOs and LUMOs indicated an excitation energy transfer (EET) mechanism from the donor moiety to the porphyrin acceptor core. All porphyrin dyads exhibited a cathodic shift in their oxidation potential suggesting facile oxidation of the porphyrin core due to π‐extension and the presence of electron‐donating moieties. Finally, femtosecond transient absorption spectral studies were performed to secure evidence of excitation transfer and kinetic information of the energy transfer event in the dyads.

β-Pyrrole Functionalized Push or Pull Porphyrins: Excited Charge Transfer Promoted Singlet Oxygen Generation

“…Negative peaks at 554 nm corresponding to ground state bleach (GSB), and at 600 and 660 nm range due to the stimulated emission (SE) were also witnessed (see spectrum at 0.44 ps). 50,51 Decay/ recovery of the positive and negative peaks was accompanied by a new set of signals with peak maxima at 490, 664, and 688 nm (see spectrum at 322 ps). These spectral features were consistent with the spectrum obtained upon the first reduction of 2b generating ZnP •d − suggesting the occurrence of charge transfer (note: spectral features of TPA •+ are buried under the ESA peaks of 2b in the 450 nm range).…”

Isomeric Pyrene–Porphyrins for Efficient Dye-Sensitized Solar Cells: An Unexpected Enhancement of the Photovoltaic Performance upon Structural Modification

“…Pyrene has also been used to modify porphyrins for a number of applications, including dye-sensitized or polymer solar cells, − carbon nanotubes, − fluorescence resonance energy transfer and charge transfer, − two-photon absorption, singlet oxygen generation (for photodynamic therapy or PDT), , the oxygen evolution reaction, and dendrimers. − In these pyrene–porphyrin systems, pyrene usually serves as the donor and the porphyrin acts as the acceptor. , …”

“…20−22 In these pyrene−porphyrin systems, pyrene usually serves as the donor and the porphyrin acts as the acceptor. 27,28 For solar cell applications, 11−16 the reported pyrene− porphyrins are all conjugated with a terminal pyrene group. In this work, we further modify pyrene−porphyrins by attaching an additional electron-donating group to the pyrene.…”