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

Abstract

Directly linked to promote strong intramolecular interactions, donor–acceptor dyads and a donor–acceptor–donor triad featuring zinc phthalocyanine (ZnPc) as electron donor and perylenediimide (PDI) as electron acceptor have been synthesized and characterized. Owing to complementary absorption features of the entities, improved light absorption was witnessed in these conjugates. The optimized geometry and electronic structures showed the majority of the highest occupied molecular orbital (HOMO) on the ZnPc entity, whereas the lowest unoccupied molecular orbital (LUMO) was on the PDI entity, suggesting that the charge‐separated states would be ZnPc+–PDI.−. The electrochemical and free‐energy calculations suggested exothermic energy and/or electron transfer processes via the singlet states of PDI or ZnPc entities depending on the excitation wavelength of the laser used. The measured rates using femtosecond pump‐probe spectroscopy coupled with global analysis of transient data revealed ultrafast energy transfer from 1PDI* to ZnPc followed by charge separation. However, when ZnPc was selectively excited, only electron transfer was witnessed wherein the time constants for forward and reverse electron transfer processes followed Marcus predictions. The absorption in a wide section of the solar spectrum and the ultrafast charge separation suggest the usefulness of these systems as good photosynthetic models.

Molecular Engineering of Multifunctional Metallophthalocyanine-Containing Framework Materials

“…Covalently linked systems can offer several advantages over supramolecular assembled ones, such as closer proximities and modulation of electronic properties in the ground and excited states . The relative distances of the D–A moieties, orientation, aggregation and electronic coupling of covalently linked D–A complexes have also been known to crucially affect the yields and kinetics of charge transfer in D–A systems …”

“…PDIs have had central roles as electron acceptors in artificial photosynthesis and D–A systems due to their interesting properties, stability, and ability to extend charge separation lifetimes . Guldi and co-workers observed that modifications of two ZnPcs to the positions of a central anthraquinone (Figure a) changed the aggregation status of the triads, which altered the kinetics of these electron transfer reactions .…”

Unsymmetrical Squaraine Dye-Based Organic Photodetector Exhibiting Enhanced Near-Infrared Sensitivity

“…In view of this, there is a growing interest in the use of organic semiconductors which can be solution-processed onto large-area flexible surfaces using conventional printing technologies to provide affordable photodetectors. Although the use of several NIR dyes including cyanines, − phthalocyanines, , and porphyrins , as organic semiconductors for the development of NIR organic photodetectors (OPDs) has been explored, several issues including low solubility, decreased stability with decrease in the band gap, and inability to form uniform films have remained as important issues that need to be addressed. Recently, there has been a growing interest in the use of a class of ambipolar molecules, namely, symmetric SQ dyes.…”

Orthogonal carbazole-perylene bisimide pentad: a photoconversion-tunable photosensitizer with diversified excitation and excited-state relaxation pathways

“…Archetypal perylene bisimide (PBI) frequently serves as electron-accepting materials due to its substantial electron affinities and other favored properties, such as intense absorption in the wide range of visible light, near unity fluorescence quantum yield, easily obtainable derivatives and robust chemical-/thermal-/photo-stability [15][16][17]. Covalent or noncovalent linking of PBI moieties and other electron donors has generated plenty of dyads, triads, tetrads, polyads, and so on [18][19][20][21][22]. The push-pull electronic effect between electron donors and PBI results in enlarged range of light harvesting and enhances the sensitivity toward microenvironment while the original high absorption coefficient and robustness are maintained.…”