Effects of anion coordination on the fluorescence of a photo-induced electron transfer (PET) sensor complexed with metal ions

Abstract

Whether π contacts between the fluorophore of the photoinduced electron transfer (PET) sensor adpa ((N-(9-anthracenylmethyl)-N-(2-pyridinylmethyl)-2-pyridinemethanamine) and complexed metal ions or coordinated halide ions control the fluorescence intensity of adpa is further investigated via fluorescence, absorbance and density functional theory (DFT) studies. Three metal-adpa complexes were studied and the crystal structures of [Cd(adpa)I 2 ] (1), [Hg(adpa)I 2 ] (2), [Zn(adpa)Cl 2 ](H 2 O) 2 (3) and [Cd(adpa)S 2 O 3 ] 2 (4) are reported. Unlike Cl-, Br-, SCNand S 2 O 3 2-, which cause an increase in fluorescence intensity upon binding to Cd II (adpa) due to the disruption of metal-fluorophore π contacts, coordination of Ito the Cd II (adpa) complex strongly decreases fluorescence intensity. The same trend was found with the addition of Ito the Hg II (adpa) and Zn II (adpa) complexes. However, the causes of fluorescence quenching associated with three metal complexes are not necessarily the same. The structure of 3 shows that the anthracenyl fluorophore does not form a π contact with the Zn, relating to the strong CHEF (chelation enhanced fluorescence) effect Zn II shows with adpa. The absorbance study suggests that the fluorescence quenching of the Zn II (adpa) complex with Iaddition is due to collisional quenching. Fluorescence quenching in the Hg(adpa)I 2 complex is attributed to the long Hg-N bond of 2.788 Å to the central N donor of the adpa in 2, which causes quenching by a PET effect from the weakly coordinated N donor. The quenching mechanism associated with the Cd II (adpa)I 2 complex seems to be more subtle. Structure 1 shows the nearest Cd•••C distance to the anthracenyl fluorophore of adpa of 3.554 Å, where such long distances are usually associated with increases in fluorescence intensity, rather than quenching. Density functional theory (DFT) studies showed that there is structural change in the excited state of the Cd II (adpa)I 2 complex, which triggers a reordering of frontier molecular orbitals. This leads to the involvement of charge transfer from the fluorophore to the iodine in the S 1  S 0 transition, which is forbidden.

Synthesis, structure–fluorescence relationships and density functional theory studies of novel naphthalimide–piperazine–pyridine-based polystyrene sensors for Hg(ii) detection

“…When a uorophore links with an electron-donating group (it generally includes one or more amido N-atoms), the photoinduced electron transfer (PET) will occur. [37][38][39][40] In our system, the introduction of the electron-donating recognition group 1-(pyridin-2-ylmethyl)piperazine into the naphthalene ring just forms a push-pull electronic mode with electron-withdrawing imide part. The PET process is easy to occur, thus changing the optical properties of naphthalimide.…”

Wavelike zinc coordination polymers: anion-modulated ligand conformation and fluorescence detection of 4-aminobenzylamine

“…Therefore, it appeared that halide anions could not only modulate the coordination mode and conformation of the bpycz ligand to advance the extended wavelike chain structures of 1 and 2 but could also slightly tune their emission behaviors in suspensions. 40,41 Fluorescence detection of the amines Compounds 1 and 2 possessed excellent water stability and acid-base resistance as well as high luminescence properties, which encouraged us to assess their potential in the fluorescence detection of amines in water. A series of amines including ethylamine (NH 2 Et), diethylamine (NHEt 2 ), trimethylamine (NEt 3 ), ethylenediamine (en), aniline (PhNH 2 ), 4-aminobenzylamine (4-ABA), o-phenylenediamine (o-PDA), p-phenylenediamine (p-PDA), 4-aminophenol (4-AP), and dopamine (DP) were chosen as models.…”

Chromophore appended DPA-based copper(ii) complexes with a diimine motif towards DNA binding and fragmentation studies

“…23,24 Due to their planarity and extended conjugation, they have an extensive range of applications including biological activities, 25 LEDs, 26 molecular logic circuits and sensors (for Zn( ii ), sugars, alkali metals, and pyrophosphate). 27,28 An anthracene appended DPA ligand and its corresponding metal complexes were exemplified in the area of coordination chemistry including inorganic biochemistry, magnetism, etc ., such as DNA-photodamage 29 and DNA cleavage, 30 and in luminescence studies, 31 including temperature-controlled switching between single and dual emissive properties 32 and photoactive release of NO. 33 These types of complexes display substantial activities against Gram-positive bacteria, and have antifungal activities.…”