Towards simple and efficient molecular reporters: combining electron transfer and charge transfer in functional dyes of donor–acceptor–spacer–donor constitution

Abstract

Two 1-phenyl-3-R-5-(4-dimethylaminophenyl)-∆ 2 -pyrazolines which are functionalized with the heterocyclic acceptors R = pyridin-2-yl and quinolin-2-yl have been studied as simple and efficient molecular reporters that can be used for multimodal signaling of two different chemical analytes. As revealed by solvatochromic studies including a reference compound (R = 4-chlorophenyl), for derivatives with electron accepting 3-R-substituents in highly polar solvents, the strongly emissive charge-transfer (CT) state of the basic 1-phenyl-3-R-∆ 2 -pyrazoline chromophore is (partly) quenched by a fast intramolecular electron transfer (ET) from the electron-rich but electronically decoupled 5-receptor. In the case of the 3-pyridin-2-yl and 3-quinolin-2-yl derivatives, this donor-acceptor-spacer-donor constitution allows to address the analyte-sensitive CT and ET processes separately by two different chemical stimuli. Metal ion binding to the 3-acceptor position and/or protonation of 3-acceptor and 5-donor lead to various changes of spectral band positions or band intensities, offering a variety of possible detection modes by the choice of absorption, excitation, and emission wavelenghts.

Differential Tuning of the Electron Transfer Parameters in 1,3,5-Triarylpyrazolines: A Rational Design Approach for Optimizing the Contrast Ratio of Fluorescent Probes

“…As outlined above, tuning of the ET driving force −Δ G et is pivotal for optimizing the contrast ratio of PET sensors. To explore whether the differential tuning strategy can be used for the latter purpose, we next synthesized a compound series containing a dimethylamino group which serves as the quenching electron donor (Chart ) . Protonation of the amino nitrogen lone pair is expected to sharply increase the donor potential, which in turn should result in a quantum yield increase.…”

Photochemical and Photobiological Properties of Pyridyl-pyrazol(in)e-Based Ruthenium(II) Complexes with Sub-micromolar Cytotoxicity for Phototherapy

“…The regular 3-(pyrid-2-yl)-4,5-dihydropyrazoles were synthesized from 2-acetylpyridine via a Claisen− Schmidt condensation with aromatic aldehydes, followed by heterocyclization of chalcones to pyrazolines with hydrazine hydrate 65 or phenylhydrazine. 66 To expand the structure− activity relationships, we carried out the oxidation of the pyrazolines to pyrazoles 67 and synthesized the inverse 1-(pyrid-2-yl)-pyrazoline ligands 68 (Scheme S1). The Ru(II) complexes 1−12 (Chart 3) were synthesized from a racemic mixture of the Δ and Λ enantiomers of the Ru(II) starting materials, and form a mixture of enantiomers upon coordination of the pyridyl-pyrazol(in)e ligands.…”

“…The regular 3-(pyrid-2-yl)-4,5-dihydropyrazoles were synthesized from 2-acetylpyridine via a Claisen–Schmidt condensation with aromatic aldehydes, followed by heterocyclization of chalcones to pyrazolines with hydrazine hydrate or phenylhydrazine . To expand the structure–activity relationships, we carried out the oxidation of the pyrazolines to pyrazoles and synthesized the inverse 1-(pyrid-2-yl)-pyrazoline ligands (Scheme S1).…”