Solvent-Triggered Long-Range Proton Transport in 7-Hydroxyquinoline Using a Sulfonamide Transporter Group

Abstract

The ability of long-range proton transport by substitution of 7-hydroxyquinoline at the eighth position with sulfonamide and sulfonylhydrazone rotor units to act as a cranearm has been studied. Different proton transport pathways triggered by different stimuli have been established depending on the structure of the crane-arms. Solvent-driven proton switching from OH to the quinoline nitrogen (N quin ) site, facilitated by a sulfonamide transporter group in polar protic and aprotic solvents, has been confirmed by optical (absorption and fluorescence) and NMR spectroscopies as well as by single-crystal X-ray structure analysis. Photoinduced long-range proton transport to the N quin site upon 340 nm UV light irradiation has been estimated in sulfonylhydrazone, which is not sensitive to solvent-driven switching. Both compounds have exhibited acid-triggered switching by trifluoroacetic acid due to the formation of a stable six-membered intramolecular hydrogen bonding interaction between the protonated N quin and crane-arm. The structures of acid-switched form were confirmed by NMR spectroscopy and single-crystal X-ray structure analysis. The behavior of the compounds suggests a big step forward in the advanced proton pump-switching architecture because they cover three distinct driving forces in the switching process: solvent, light, and acid.

Tuning ESIPT-coupled luminescence by expanding π-conjugation of a proton acceptor moiety in ESIPT-capable zinc(ii) complexes with 1-hydroxy-1H-imidazole-based ligands

“…[109][110][111][112] Interestingly, the proton-transfer properties of these systems make them analogous to the C-OH -CvO tautomeric systems. [113][114][115][116][117][118] The ability of 1-hydroxy-1H-imidazoles to form N-hydroxy and N-oxide tautomers had not been used in the engineering of ESIPT-fluorophores until our recent works. 105,106,119 It is well known that the proton transfer abilities and emission properties of ESIPT-capable molecules can be tuned by substitution on the proton-donating and protonaccepting cores, as well as by the degree of π-conjugation.…”

“…109–112 Interestingly, the proton-transfer properties of these systems make them analogous to the C–OH – CO tautomeric systems. 113–118 The ability of 1-hydroxy-1 H -imidazoles to form N -hydroxy and N -oxide tautomers had not been used in the engineering of ESIPT-fluorophores until our recent works. 105,106,119…”

Long-Range Proton Transfer in 7-Hydroxy-Quinoline-Based Azomethine Dyes: A Hidden Reason for the Low Efficiency

“…Recently, we have reported several classes of proton craning switches, based on 7HQ , where the azomethine group plays a role of a crane unit, providing, in some cases, truly intramolecular long-range PT upon irradiation [ 23 , 24 , 25 ]. It was shown ( Scheme 1 ) that the proton is transferred from the 7HQ oxygen atom to the basic nitrogen through series of short-range PT steps, accompanied by intramolecular rotation around the axle binding the tautomeric and crane units.…”

First 1-hydroxy-1H-imidazole-based ESIPT emitter with an O–H⋯O intramolecular hydrogen bond: ESIPT-triggered TICT and speciation in solution

“…The ESIPT photoreaction in ESIPT-capable molecules depends strongly on the nature of media, [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50] on substituents introduced in the core of an ESIPT-capable molecule and on the degree of p-conjugation between different moieties of the molecule. [51][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67][68][69] These factors affect the electronic structure of the molecule and can induce barriers between the normal and tautomeric forms on the potential energy surfaces (PESs) in the excited state, causing partial or even full frustration of the proton transfer.…”