Profluorescent verdazyl radicals – synthesis and characterization

Abstract

The synthesis and characterization of various 6-oxo-verdazyl radicals and their diamagnetic styryl radical trapping products are presented.

Boron difluorides with formazanate ligands: redox-switchable fluorescent dyes with large stokes shifts

“…27 EPR spectroscopy for the radical anions [1] •− shows broad, featureless resonances at g ∼ 2, indicative of ligand-based radicals. While related organic verdazyl radicals show hyperfine interactions with the N nuclei, 24,28 these are absent in the boron systems studied here. DFT calculations (see the ESI †) suggest that the hyperfine coupling constants in [1a] •− are indeed smaller for the boron compounds reported here than those in organic analogues.…”

“…Recently, Studer and co-workers used verdazyl radicals as "pro-fluorescent" radical probes. 24 Here we describe the synthesis and characterization of (formazanate)boron complexes (LBF 2 , 1, Scheme 1) as well as the corresponding 1-electron reduction products, the radical anions [LBF 2 ] •− (1 •− ), and discuss the impact of electronic and steric effects on both the optical and redox properties. We show that the neutral compounds 1 are fluorescent with large Stokes shifts, whereas in the radical anions 1 •− the fluorescence is quenched.…”

Syntheses, spectroscopy, and crystal structures of 3-(4-bromophenyl)-1,5-diphenylformazan and the 3-(4-bromophenyl)-1,5-diphenylverdazyl radical and the crystal structure of the by-product 5-anilino-3-(4-bromophenyl)-1-phenyl-1H-1,2,4-triazole

“…A few years after Kuhn's discovery, syntheses leading to the orange 6-oxo-and 6-thioxoverdazyls were developed (Neugebauer & Fischer, 1980;Neugebauer et al, 1988). As of late, verdazyls experience renewed interest, partially as a result of the improvements concerning their syntheses, enabling the introduction of a large variety of substitution patterns (Paré et al, 2005;Bancerz et al, 2012;Matuschek et al, 2015;Le et al, 2017). Such tailor-made radicals have possible applications as fundamental building blocks in molecular magnets or in spintronic materials (Koivisto & Hicks, 2005;Train et al, 2009;Ratera & Veciana, 2012).…”

Intersystem Crossing in Naphthalenediimide–Oxoverdazyl Dyads: Synthesis and Study of the Photophysical Properties

“…The formation of the doublet spin state is beneficial for ISC:t he ISC of the chromophore is within the overall D n !D 1 transition of the dyad, whichi sas pin-allowed process (herein for the D n state, the chromophore is in the singlet state;f or the D 1 state, the chromophore is in the triplet state). [9,10] Previously,r adical-labeled fluorophoresh ave mainly been used as fluorescent molecular probesf or the selective detection of reactive radicals, [8,[11][12][13][14] based on the quenching of fluorescenceb yt he attachedradicalo nt he fluorophore, and fluorescencer ecoveryo ft he fluorophore upon reactiono ft he radical with the analytes. However,t he quenching mechanisms of the radicalo nt he fluorescence were not studied in detail.…”