Synthesis of Bisimidazole Derivatives for Selective Sensing of Fluoride Ion

Abstract

Rapid and efficient analysis of fluoride ion is crucial to providing key information for fluoride ion hazard assessment and pollution management. In this study, we synthesized one symmetrical structure called 1,4-bis(4,5-diphenyl-1H-imidazol-2-yl)benzene (1a) and two asymmetrical structures, namely 2-(4-(4,5-diphenyl-1H-imidazol-2-yl)phenyl)-1H-phenanthro(9,10-d)imidazole (1b) and 2-(4-(4,5-diphenyl-1H-imidazol-2-yl)phenyl)-1H-imidazo(4,5-f)(1,10)phenanthroline (1c), which served as an efficient anion sensor for fluoride ion over a wide range of other anions (Cl−, Br−, I−, NO3−, ClO4−, HSO4−, BF4−, and PF6−) owing to imidazole group in the main backbone. The absorption intensity of compound 1a at λmax 358 nm slightly decreased; however, a new band at λmax 414 nm appeared upon the addition of fluoride ion, while no evident change occurred upon the addition of eight other anions. The photoluminescence intensity of compound 1a at λmax 426 nm was nearly quenched and fluorescence emission spectra were broadened when fluoride ion was added into dimethyl sulfoxide (DMSO) solution of compound 1a. Compared with the optical behaviors of the DMSO solution of compound 1a in the presence of Bu4N+F−, compounds 1b and 1c exhibited considerable sensitivity to fluoride ion due to the increase in coplanarity. Furthermore, compared with the fluorescence emission behaviors of the DMSO solutions of compounds 1a and 1b in the presence of Bu4N+F−, compound 1c exhibited the most significant sensitivity to fluoride ion due to the charge transfer enhancement. Consequently, the detection limits of compounds 1a–1c increased from 5.47 × 10−6 M to 4.21 × 10−6 M to 9.12 × 10−7 M. Furthermore, the largest red shift (75 nm) of the DMSO solution compound 1c in the presence of fluoride ion can be observed. Our results suggest that the increase in coplanarity and the introduction of electron-withdrawing groups to the imidazole backbone can improve the performance in detecting fluoride ion.

Synthesis of Tris-pillar[5]arene and Its Association with Phenothiazine Dye: Colorimetric Recognition of Anions

“…Low charge density and the large size of anions compared to cations are the main hindrances for creating selective sensors of anions. The introduction of amide, hydroxyl, urea, and thiourea fragments into receptor structures allow for the formation of additional coordination sites for more effective and selective binding of anionic substrates by hydrogen bonds [4,5,6]. One of the most widespread approaches to constructing macrocycle-derived anion sensors is using a macrocyclic platform for spatial preorganization of proton donating groups, which provides conformity of the receptors spatial structure to the substrate [7].…”

A fundamental role of the solvent polarity and remote substitution of the 2-(4-R-phenyl)-1H-imidazo[4,5-f][1,10]phenanthroline framework in controlling the ground- and excited-state properties of Re(i) chromophores [ReCl(CO)3(R-C6H4-imphen)]

“…The phosphorescent nature of the emission of 1-5 is supported by the high sensitivity of the photoluminescence intensity toward O 2 , large Stokes shifts and excited state lifetimes on a microsecond or sub-microsecond scale. The contribution of 3 MLCT is reflected by a structureless emission profile, a noticeable hypsochromic shift of the emission accompanied by an increase in the emission lifetimes of 1-5 upon going from the solution to the low-temperature matrix. As a result of the lack of solvent reorganization in rigid matrices, the energy of 3 MLCT increased, leading to an increase in the excited-to-ground state energy gap and a noticeable decrease in the non-radiative decay rate constant.…”

“…During the last two decades, imidazo [4,5-f ] [1,10]phenanthrolines have attracted widespread attention owing to their remarkable antitumor and luminescence properties which make these compounds useful for employment as luminescence sensors, [1][2][3][4][5] OLED components, 6,7 and inhibitors against various tumor cells. [8][9][10][11][12][13][14] A great advantage of these systems is that they involve a relatively simple synthetic procedure and there is a possibility of introducing all types of substituents into the imidazole ring at the 1H-and C2-positions, including both electron-withdrawing and electron-donating groups, showing different lipophilicities and steric hindrances, directly (via the covalent bond) or through an aryl/heterocycle bridge.…”

“…[8][9][10][11][12][13][14] A great advantage of these systems is that they involve a relatively simple synthetic procedure and there is a possibility of introducing all types of substituents into the imidazole ring at the 1H-and C2-positions, including both electron-withdrawing and electron-donating groups, showing different lipophilicities and steric hindrances, directly (via the covalent bond) or through an aryl/heterocycle bridge. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Possessing the 1,10-phenanthroline unit with strong abilities to bind transition metals, imidazo [4,5-f ] [1,10] phenanthrolines have also become very popular ligands for controlling the photophysical and antiproliferative behaviour of transition metal complexes. They have been combined with numerous transition metal ions including Cu(I), [21][22][23][24][25] Cu(II), [26][27][28] Ru(II), [29][30][31][32][33][34][35]<...…”

“…49,57,58,61,[75][76][77][78] In particular, a beneficial role of electron-rich remote substituents was revealed for rhenium(I) κ 2 N-tricarbonyl complexes with 4′-(4-substituted-phenyl)-2,2′:6′,2″-terpyridine ligands. The change in the lowest triplet excited state from 3 MLCT to 3 ILCT resulted in a pronounced enhancement of the excited-state lifetime of [ReCl (CO) 3 (R-C 6 H 4 -terpy-κ 2 N)]. 79 The ground-and excited-state properties of 1-4 were investigated experimentally using cyclic voltammetry, absorbance and emission spectroscopy and transient absorption spec-troscopy, as well as theoretically on the basis of density functional theory (DFT).…”