Acid–base properties of bis-pyrazolopyridine derivatives in nonaqueous solutions

Synthesis of Fluorescent 1,7-Dipyridyl-bis-pyrazolo[3,4-b:4′,3′-e]pyridines: Design of Reversible Chemosensors for Nanomolar Detection of Cu2+

“…14,17−20,22a,23 Thus, we have hypothesized that PBPs 6a – 6e have the necessary features for their use in the detection of metal ions through the fluorescence quenching process based on TICT mechanisms (Scheme 1b). 8−10,12 In this work, compounds 6a – 6e showed a high fluorescence emission in different solvents and large Stokes shifts due to the TICT process being favored. In addition, the presence of a 2-pyridyl group at positions 1 and 7 of the bis-pyrazolopyridinic core has not yet been reported.…”

“…Consequently, these photophysical results confirm that fluorescence properties of bis-pyrazolopyridines are governed by a TICT mechanism sensitive to sterically restricted environments that limit molecular rotations around aryl–BP bonds. 9,10 The TICT phenomenon is responsible for this type of compounds having high fluorescence quantum yields, and also, ligands 6 can be successfully used as fluorescent probes of metal ions. 9−12,23 Compound 6b was used in further studies of the design of fluorescent probes of metal ions because this ligand displayed the strongest fluorescence intensity.…”

“…As mentioned above, these ligands exhibited strong blue light emission by a TICT fluorescence mechanism, typical of compounds containing the bis-pyrazolopyridinic core (BP), which is sensitive to environments that limit molecular rotations around aryl–BP bonds of 6a – 6e . 8−10 Accordingly, upon addition of some metal ions M 2+ to a dissolution of these tridentate ligands, fluorescence quenching is observed as a result of the coordination 6–M 2+ , which results in the increase of their structural rigidity and inhibition of the TICT processes. The sensing mechanism of 6b toward Cu 2+ , a possible ligand–metal charge transfer, and its reversibility process are shown in Figure 5.…”

“…These compounds are novel tridentate ligands, whose synthesis proceeds by a three-step sequence under microwave starting from 2-chloropyridine ( 1 ). Ligands 6a – 6e contain a fused tricyclic structure that is dialkyl- and triaryl-substituted and also have three pyridine nitrogen atoms (CN:) suitably situated to achieve the formation of chelates. ,− ,, Thus, we have hypothesized that PBPs 6a – 6e have the necessary features for their use in the detection of metal ions through the fluorescence quenching process based on TICT mechanisms (Scheme b). − , In this work, compounds 6a – 6e showed a high fluorescence emission in different solvents and large Stokes shifts due to the TICT process being favored. In addition, the presence of a 2-pyridyl group at positions 1 and 7 of the bis-pyrazolopyridinic core has not yet been reported.…”

“…BPs have received little biological interest, although they have been attractive for photophysical applications , due to their 1,4,7-triaryl-substituted derivatives exhibiting a high fluorescence in both solution and solid state by a typical twisted intramolecular charge transfer (TICT) mechanism (Figure ). , …”