Excited State Intramolecular Proton Transfer in Electron-Rich and Electron-Poor Derivatives of 10-Hydroxybenzo[h]quinoline

Abstract

Eight previously inaccessible derivatives of 10-hydroxybenzo[h]quinoline were prepared via a straightforward strategy comprising formation of the benzo[h]quinoline skeleton followed by C-H acetoxylation at position 10. The occurrence of excited state intramolecular proton transfer (ESIPT) was detected in all cases since emission was observed only from the excited keto-tautomer. Studies on derivatives bearing both electron-donating and electron-withdrawing groups adjacent to the pyridine ring allowed us to identify some design patterns giving rise to NIR emission and large Stokes shifts. For a derivative of 10-hydroxybenzo[c]acridine, emission at 745 nm was observed, one of the lowest energy fluorescence ever reported for ESIPT system. On the basis of time-resolved measurements, proton transfer was found to be extremely fast with time constants in the range (0.08-0.45 ps).

Iridium‐Catalyzed Direct C−H Amidation Polymerization: Step‐Growth Polymerization by C−N Bond Formation via C−H Activation to Give Fluorescent Polysulfonamides

“…[12] In addition, this interpretation was also supported by emission properties that were independent of awide range of solvent polarity (see Figure S4). [13] Theprevious examples of fluorescent polymers exhibiting the ESIPT process contained ap henolic À OH moiety as ahydrogen-bond donor and displayed large Stokes shifts (86-255 nm) with only weak fluorescence (F F = 0.003-0.06). [14] However,strong fluorescence (quantum yields of up to 0.45;s ee Table S7) was observed from P1-P6,w hich contain the sulfonamide N À Hg roup as the hydrogen-bond donor because the sulfonamide moiety is conformationally locked and rigid, thereby reducing the probability of other non-radiative decay processes.T hese intriguing fluorescence properties were also observed in the film state,w here large Stokes shifts (153-173 nm) and high quantum yields of up to 0.49 without significant self-quenching were observed (see Table S7 and Figure S2).…”

On the Fine‐Tuning of the Excited‐State Intramolecular Proton Transfer (ESIPT) Process in 2‐(2′‐Hydroxybenzofuran)benzazole (HBBX) Dyes

“…[3] Therefore, ESIPT emission is characterized by enhancedS tokess hifts as compared with regularf luorophores, and as trong dependence of the proton-transfer strength and fluorescencei ntensity on the environment.T his is especially remarkable in the case of protic media, which can induce ap artialf rustrationo ft he protont ransfert hrough ah ydrogen-bonded stabilization of the enol speciesi nt he most commonc ase, that is, of an ESIPT process that consistso fa nenol/keto tautomerization. Of these structures, one can quote reported ESIPT emitters based on 2,2'-bipyridine-diol, [5] benzoimidazol indolizines, [6] imidazoles, [7] hydroxytriazine, [8] imidazo [1,2-a]pyridine, [9] or benzoquinoline, [10] among other derivatives. [4] The ESIPT process has been revealed in both natural and synthetic chromophoric structures that featureastrong hydrogen bond in the grounds tate in their p-conjugated molecular core.…”

Deuterium Isotope Effects on 13C-NMR Chemical Shifts of 10-Hydroxybenzo[h]quinolines

“…For data in CDCl 3 see Ref. [22]; c Solvent THF-d 8 :CDCl 3 : (2:1); c Values in parentheses, solvent DMF- d 7 . d Overlapping lines.…”