Intriguing multichannel photoinduced electron transfer in lanthanide(iii)–diphenylamine systems

Abstract

Photoinduced electron transfer (PET) and charge transfer (CT) interactions of trivalent lanthanide ions (Ln(3+)) with a fluorogenic diphenylamine (DPA) donor in aqueous solution have been investigated. Present donor-acceptor systems have a relevance to the leaching out and mitigation of lanthanide ions in the geoenvironment where DPA finds its presence as industrial and agricultural waste. The formation of weak ground state CT complexes in the present systems is confirmed from ground state absorption studies. There is no emissive exciplex formation as evidenced from steady-state (SS) fluorescence measurements. SS fluorescence quenching results, however, indicate substantial static quenching, attributed to ground state complex formation. Time-resolved (TR) fluorescence quenching results show a quite efficient dynamic quenching process. It is established that the TR fluorescence quenching of DPA by lanthanide ions is not due to energy transfer but due to PET from excited DPA to Ln(3+). Direct evidence for the PET mechanism is obtained from laser flash photolysis measurements where a transient absorption band at around 670 nm for the DPA cation is clearly evident. The time constant for DPA cation growth confirms that PET occurs from the excited S1 state of DPA to lanthanide ions. No correlation is, however, observed for the estimated quenching constants with the free energy changes of the PET reactions, due to the participation of multiple PET channels involving vacant electronic states of lanthanide ions. As realized, lanthanide ions are complex electron acceptors in the PET reactions and many extensive follow up studies are expected to understand the details of the multichannel PET in these geologically important redox systems.

Effect of Ionic Liquids as Cosurfactants on Photoinduced Electron Transfer in Tetronic Micelles

“…The ILs are environmentally benign molten electrolytes, considered as “green solvents”, having unique properties like low vapor pressure, nonflammability, high ionic mobility, and excellent chemical stability. , ILs that possess hydrophobic alkyl chains at their cations show properties similar to conventional surfactants, behaving as surface-active ILs (SAILs). , Being biologically friendly, SAILs have better prospects as cosurfactants than common surfactants to modulate the characteristics of copolymer micelles. ,− However, only few studies have been reported so far on the use of ILs as cosurfactants, focusing mainly on the changes in the micellar size and aggregation number. − To the best of our knowledge, changes in the physicochemical characteristics of micelles, such as micropolarity, microviscosity, solvent relaxation dynamics, and so on, and their consequent effect on bimolecular PET reactions in tetronic–IL mixed micelles have not been attempted so far. Because the necessary structural parameters of T1304–IL mixed micelles using 1-alkyl-3-methylimidazolium tetrafluoroborate ([C n MIm]­[BF 4 ]) series of ILs are readily available in the literature, we have selected these assemblies to study PET reactions involving a series of coumarin dyes as electron acceptors and N , N -dimethylaniline (DMAN) as the electron donor.…”

1-Azathioxanthone Appended Europium(III) Complexes with Excita-tion at 405 nm: Consequences for Lanthanide Luminescence based Bioimaging on Commercial Microscopes

“…27 Bromination in the α-position on 2-methyl-1-azathioxanone has previously been described in the literature using a Wohl-Ziegler bromination. 28,29 However, it was not possible to reproduce this reaction in our labs. Though multiple modifications were attempted in the reaction conditions, the reaction either did not yield the desired molecules in high enough yields to continue the synthetic procedures or gave undesired products.…”

“…As an alternative, a patent describing functionalization of the α-position was used with minor modifications, see SI for experimental details. 29,30 In the preferred procedure, see Scheme 1, the parent 2-methyl-1-azathioxanthone derivatives were oxidized using iodide, iron(III)sulfate, TFA, and tert-butyl iodide in DMSO. The reaction was performed at least three times for each derivative, and it was shown that tert-butyl iodide is not required for the oxidation to occur.…”

“…The reduction potentials used in the figure are EuIII/EuII = -0.35 V in water vs. NHE and for thioxanthone in DMF: 1.62 V vs. NHE. 29,41 The luminescence lifetimes were measured in PBS (pH = 7.4) prepared from H2O and D2O to determine the number of solvent molecules coordinated to the europium(III) center using the modified Horrocks' equation. 42 The lifetimes of 1 and 3 are as expected, while the lifetime of too short.…”

Tandem Detection of Sub-Nano Molar Level CN– and Hg2+ in Aqueous Medium by a Suitable Molecular Sensor: A Viable Solution for Detection of CN– and Development of the RGB-Based Sensory Device

“…The nonfluorescent chemosensor exhibited an infirm emission spectrum at 355 nm by the excitation at 290 nm, which concomitantly up surged upon consecutive addition of CN – along with the simultaneous red shifting of the peak position (Figure S10; Supporting Information). The bathochromic spectral shift of the sensor in presence of CN – clearly suggested the favorable ICT process. − Additionally, the turn-on fluorescence response in presence of CN – may be the consequence of the constraint in the PET as a result of the sensor–CN – interaction. − …”