Luminescent Excited‐State Intramolecular Proton‐Transfer (ESIPT) Dyes Based on 4‐Alkyne‐Functionalized [2,2′‐Bipyridine]‐3,3′‐diol Dyes

Abstract

Functionalized 6,6'-dimethyl-3,3'-dihydroxy-2,2'-bipyridine dyes (BP(OH)(2)) exhibit relatively intense fluorescence from the relaxed excited state formed by excited-state intramolecular proton transfer (ESIPT). Bromo functionalization of (BP(OH)(2)) species followed by palladium(0)-catalyzed reactions allows the connection (via alkyne tethers) of functional groups, such as the singlet-emitter diazaboraindacene (bodipy) group or a chelating module (terpyridine; terpy). The X-ray structure of the terpy-based compound confirms the planarity of the 3,3'-dihydroxy-bipyridine unit. The new dyes exhibit relatively intense emission on the nanosecond timescale when in fluid solution, in the solid state at 298 K, and in rigid glasses at 77 K. In some cases, the excitation wavelength luminescence was observed and attributed to 1) inefficiency of the ESIPT process in particular compounds when not enough vibrational energy is introduced in the Franck-Condon state, which is populated by direct light excitation or 2) the presence of an additional excited state that deactivates to the ground state without undergoing the ESIPT process. For some selected species, the effect of the addition of zinc salts on the absorption and luminescence spectra was investigated. In particular, significant fluorescence changes were observed as a consequence of probable consecutive formation of a 1:1 and 1:2 molecular ratio of ligand/zinc adducts owing to coordination of Zn(II) ions by the bipyridyldiol moieties, except when an additional terpyridine subunit is present. In fact, this latter species preferentially coordinates to the Zn(II) ion in a 1:1 molecular ratio and further inhibits Zn(II) interaction. In the hybrid Bodipy/BP(OH)(2) species, complete energy transfer from the BP(OH)(2) to the bodipy fluorophore occurs, leading to exclusive emission from the lowest-lying bodipy subunit.

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.…”

Synthetic Routes to Fluorescent Dyes Exhibiting Large Stokes Shifts

“…These results are in keeping with previous results obtained with 4-alkyne-functionalized [2,2′-bipyridine]-3,3′-diol ESIPT dye types. 30 It is instructive to take stock of the likely events that follow selective excitation into pyrene or perylene residues in the triazine dyads 15 and 16 ( Figure 13). As would be expected …”

Lumineszierende Materialien: Fixierung von π‐konjugierten und heterocyclischen Liganden mit Bor(III)

“…Diese Eigenschaft wurde zum Aufbau von Bibliotheken “intelligenter” Moleküle mit großen Emissionsquantenausbeuten genutzt 24. 25…”