Efficient Low Driving Force Charge Separation in an Electron Deficient Zn-Porphyrin−Fullerene Donor–Acceptor Conjugate

Abstract

Here, we present a novel conjugate based on a weakly electron-donating Zn(II)-meso-tetrakis(pentafluorophenyl)porphyrin linked to a strongly electron-accepting C 60 . From spectroscopic and electrochemical investigations a 1.9 eV high charge-separated state is derived. Transient absorption spectroscopy measurements analyzed by global target analysis confirmed the successful charge separation with a quantum yield of 72% despite an overall small driving force of only −0.2 eV. The chargeseparated state lifetime is in the nanosecond range. Considering that 90% of the singlet excited state energy is transiently stored in the charge-separated state, we conclude a charge separation energy efficiency of 65%.

Distance‐Dependent Electron Transfer Kinetics in Axially Connected Silicon Phthalocyanine‐Fullerene Conjugates

“…This ionic liquid significantly improves the absorption of microwave radiation, so SiPcs 3 – 5 are obtained in about one hour, with yields ranging from 20 to 30 %. These yields are comparable to those obtained in the preparation of similar compounds when a classical‐heating method is employed and using long reaction times (>12 h) . Finally, C 60 ‐SiPc‐C 60 1 and C 60 ‐SiPc‐C 60 2 are obtained through a double Prato's reaction, with sarcosine as nitrogen source and obtaining, both compounds, in a 29–30 % yield.…”

“…These yields are comparable to those obtained in the preparation of similar compounds when a classical-heating method is employed and using long reaction times (> 12 h). [8,29,30,32,34,38,39] Finally, C 60 -SiPc-C 60 1 and C 60 -SiPc-C 60 2 are obtained through a double Prato's reaction, with sarcosine as nitrogen source and obtaining, both compounds, in a 29-30 % yield. It is worth to note that, in this step, an excess of pristine C 60 is used and the reaction time is limited to 1 h, to minimize the formation of polyadducts.…”

“…[24] That is why donor-acceptor arrangements based on porphyrin/phthalocyanine and C 60 -fullerene, represent an outstanding majority. [25][26][27][28][29][30][31][32][33] In the context of donor-acceptor design, there are few examples of covalent multimodular artificial photosynthetic systems, where electron-acceptor units are arranged in the axial positions of a suitable porphyrinoid macrocycle, thus providing molecular systems that undergo photo-induced electron transfer processes in a very efficient way. [19,[34][35][36][37][38][39][40][41][42][43][44][45] One of the most versatile building-blocks is silicon phthalocyanine (SiPc), which can be easily functionalized at axial positions through a variety of functionalities.…”

“…Furthermore, upon reduction, C 60 containing systems tend to show faster charge separation and slower recombination processes, such property is important in building constructs which behave close to photosynthetic pigments for efficient light harvesting . That is why donor‐acceptor arrangements based on porphyrin/phthalocyanine and C 60 ‐fullerene, represent an outstanding majority …”

Anionic Fluorinated Zn-porphyrin Combined with Cationic Endohedral Li-fullerene for Long-Lived Photoinduced Charge Separation with Low Energy Loss

“…Porphyrins and their derivatives have been widely used in many applications such as catalysts, , nonliner optics, − switching devices, , and photovoltaics. , In the field of artificial photosynthesis, porphyrins are known as excellent light-harvesting antennas to mimicking the natural photosynthesis system because of their very intense absorption band in the visible region and excellent electron-donating properties. , Donor–acceptor complexes consisting of electron-donating porphyrins and electron-accepting fullerenes have been extensively studied for artificial photosynthesis. − The complexes generate charge-separated (CS) states by photoinduced electron transfer from porphyrins to fullerenes. The lifetime of the CS state is a key factor to improve their efficiency of energy conversion. − An extremely long-lived CS state with a lifetime of 0.38 s has been found in a covalently linked ferrocene–zinc porphyrin–free-base porphyrin–C 60 tetrad in frozen benzonitrile .…”