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In this study, molecular triads comprising two electron-deficient perylenediimides are covalently linked to a bridging electron donor, diamino-azobenzene, to give strong ground-state polarization resulting in wide-band optical coverage. Keywords: diaminoazobenzene; fluorescence spectroelectrochemistry; perylenediimide-azobenzene triad; quadrupolar charge transfer; ultrafast spectroscopy EN diaminoazobenzene fluorescence spectroelectrochemistry perylenediimide-azobenzene triad quadrupolar charge transfer ultrafast spectroscopy 1 1 1 03/03/22 20220301 NES 220301 B The transfer of charge b in covalently linked donor-acceptor systems is highly important in many areas of chemistry, artificial photosynthesis, semiconductor devices, and solar cells. Diaminoazobenzene, fluorescence spectroelectrochemistry, perylenediimide-azobenzene triad, quadrupolar charge transfer, ultrafast spectroscopy. [Extracted from the article]

Strong push-pull interactions between electron donor, diaminoazobenzene (azo), and an electron acceptor, perylenediimide (PDI), entities in the newly synthesized A-D-A type triads (A=electron acceptor and D=electron donor) and the corresponding A-D dyads are shown to reveal wide-band absorption covering the entire visible spectrum. Electrochemical studies revealed the facile reduction of PDI and relatively easier oxidation of diaminoazobenzene in the dyads and triads. Charge transfer reversal using fluorescence-spectroelectrochemistry wherein the PDI fluorescence recovery upon one-electron oxidation, deterring the charge-transfer interactions, was possible to accomplish. The charge transfer state density difference and the frontier orbitals from the DFT calculations established the electron-deficient PDI to be an electron acceptor and diaminoazobenzene to be an electron donor resulting in energetically closely positioned PDI δ- -Azo δ+ -PDI δ- quadrupolar charge-transfer states in the case of triads and Azo δ+ -PDI δ- dipolar charge-transfer states in the case of dyads. Subsequent femtosecond transient absorption spectral studies unequivocally proved the occurrence of excited-state charge transfer in these dyads and triads in benzonitrile wherein the calculated forward charge transfer rate constants, k f , were limited to instrument response factor, meaning >10 12  s -1 revealing the occurrence of ultrafast photo-events. The charge recombination rate constant, k r , was found to depend on the type of donor-acceptor conjugates, that is, it was possible to establish faster k r in the case of triads (∼10 11  s -1 ) compared to dyads (∼10 10  s -1 ). Modulating both ground and excited-state properties of PDI with the help of strong quadrupolar and dipolar charge transfer and witnessing ultrafast charge transfer events in the studied triads and dyads is borne out from the present study., (© 2022 Wiley-VCH GmbH.)

Photoinduced charge transfer and separation events in a newly synthesized azobenzene-bridged perylenediimide-dimer (PDI-dimer) are demonstrated. Trans-to-cis conversion (∼50 % efficiency) from the initial trans PDI-dimer by 355 nm pulsed laser light, and its reversal, cis-to-trans, process by 435 nm laser light irradiation has been possible to accomplish. Efficient fluorescence quenching in the PDI-dimer, more so for the cis isomer was witnessed, and such quenching increased with increasing solvent polarity. DFT-calculated geometry and electronic structures helped in visualizing the charge transfer in the PDI-dimer in both isomeric forms, and also revealed certain degree of participation of the azobenzene entity in the charge transfer events. Femtosecond transient absorption spectral studies confirmed occurrence of both charge transfer followed by charge separation in the studied PDI-dimer in both trans and cis forms in polar solvents, and the evaluated time constants from Global target analysis revealed accelerated events in the cis PDI-dimer due to proximity effects. The present study offers key insights on the role of the azobenzene bridge, and the dimer geometry in governing the excited state charge transfer and separation in symmetrically linked PDI dimer., (© 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

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 1 PDI* 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., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A fluorogenic perylenediimide-functionalized polyacrylate capable of generating color and fluorescence changes in the presence of triacetone triperoxide TATP), an improvised explosive used in terrorist attacks, under solvent-free, solid-state conditions has been developed. The material works by accumulating volatile TATP until it reaches a threshold; therefore, triggering colorimetric and fluorescent responses., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)