Understanding the Selective-Sensing Mechanism of Al³⁺ Cation by a Chemical Sensor Based on Schiff Base: A Theoretical Approach

Abstract

A methodology that allows us to explain the experimental behavior of a turn-on luminescent chemosensor is proposed and verified in 1-[(1H-1,2,4-triazole-3-ylimino)-methyl]-naphthalene-2-ol] (L1), selective to Al 3+ cations. This sensor increases its emission when interacting with ions upon excitation at 442 nm, which is denoted as the chelation-enhanced fluorescence effect. Photoinduced electron transfer is responsible for the fluorescence quenching in L1 at 335 nm, in Ni 2+ /L1 at 385 nm, and in Zn 2+ / L1 at 378 nm. In Ni 2+ /L, ligand-to-metal charge transfer (LMCT), from the molecular orbital of the ligand to the Ni 3d x 2 − y 2 orbital, can contribute to the quenching of fluorescence. Based on oscillator strength, the highest luminescence intensity of L1 at 401 nm and that of Al 3+ /L1 at 494 nm in relation to the others is evidenced. The consideration of the relative energies of the excited states and the calculation of the rate and lifetime of the electron transfer deactivation are necessary to get a good description of the sensor.

Sensing mechanism elucidation of a chemosensor based on a metal‐organic framework selective to explosive aromatic compounds

“…A precise description, both of the S 0 state and of the S 1 state, in terms of energy and structure, allowed us to explain in detail the turn‐on fluorescent mechanism of the two chemosensor luminescents based on Schiff basis selective to metal ions. [ 60,61 ]…”

“…A precise description, both of the S 0 state and of the S 1 state, in terms of energy and structure, allowed us to explain in detail the turn-on fluorescent mechanism of the two chemosensor luminescents based on Schiff basis selective to metal ions. [60,61] Considering the importance of knowing that the emissive state of chemosensor is optimized, the S 1 state of the Zn-MOF is used to understand the origin of fluorescence in this system. Thus, the optimized geometry of the S 1 state was taken as input data to calculate the electronic transitions that constitute the emission spectrum of Zn-MOF by means of TD-DFT methods.…”

Construction of a Nano‐rectangular Zn(II)‐Yb(III) Complex with Near‐Infrared Luminescent Response towards Metal Ions

“…The added metal ions may affect the LMET process in 1 due to their perturbation to the electronic structure and excited state of the Schiff base ligand, resulting in so‐called chelation enhancement of the quenching emission (CHEQ) effect. [ 34 ] For example, d‐block metal ions such as Co 2+ , Cu 2+ , Fe 3+ , Ni 2+ and Cr 3+ may quench the lanthanide luminescence through f→d energy transfers. [ 35,36 ] The luminescence response of 1 to the addition of Cd 2+ ion has been further studied through UV‐vis titration.…”

A Coumarin‐boronic Based Fluorescent “ON‐OFF” Probe for Hg2+ in Aqueous Solution

“…For 1 + Hg 2+ / 1· H 2 O + Hg 2+ complex, the HOMO is predominantly localized on the Hg 2+ central metal ion and the coordinated N, O atoms, while the LUMO is essentially spread over the whole molecule (Tables S1–S3, Supporting Information), which induced charge transfer from the Hg 2+ center to the excited moiety thus providing a fluorescence quenching result. [ 9c,34 ] Nevertheless, the calculations revealed that compound 1· H 2 O + Hg 2+ was not stable since the boric acid ester ring would break when optimized the structure at PBE0/B3LYP method.…”