Modular Fluorescent Benzobis(imidazolium) Salts:  Syntheses, Photophysical Analyses, and Applications

Abstract

A series of benzobis(imidazolium) (BBI) salts has been prepared and studied as a new class of versatile fluorescent materials. Using a high yielding, modular synthetic strategy, BBI salts with a range of functionality poised for investigating fundamental and applications-oriented characteristics, including emission wavelength tunability, solvatochromism, red-edge excitation, chemical stability, multiphoton excitation, and protein conjugation, were prepared in overall yields of 40-97%. Through structural variation, the BBIs exhibited lambda(em) ranging between 329 and 561 nm while displaying phi(f)s up to 0.91. In addition, the emission characteristics of these salts were found to exhibit strong solvent dependencies with Stokes shifts ranging from 4570 to 13 793 cm(-1), depending on the nature of the BBI core. Although red-edge effects for BBI salts with Br and BF4 counterions were found to be similar, unique characteristics were displayed by an analogue with MeSO4 anions. The stability of an amphiphilic BBI was quantified in aqueous solutions of varying pH, and >85% of the emission intensity was retained after 2 h at pH 3-9. Through multiphoton excitation experiments in aqueous solutions, a BBI salt was found to exhibit three-photon fluorescence action cross sections similar to serotonin. The application of BBI salts as fluorescent protein tags was demonstrated by conjugating bovine serum albumin to a maleimide-functionalized derivative.

Efficient Electronic Communication of Two Ruthenium Centers through a Rigid Ditopic N‐Heterocyclic Carbene Linker

“…[21] Accordingly, amination of 2,4-dinitro-1,5-dichlorobenzene with 2-aminopyridine furnished the pyridylfunctionalized product 1. Aminations performed in EtOH at 120 8C afforded 1 only after extended reaction times and furnished monosubstituted compounds as major products due presumably to the deactivating effect of the first pyridyl substituent.…”

“…X-ray quality crystals were grown by slow diffusion of Et 2 O into a MeCN solution of complex 9 at À20 8C. Elemental analysis calcd (%) for C 21 Ru (764.45): C 32.99,H 3.03,N 12.83;found: C 33.23,H 2.91,N 13.04.…”

Benzobis(imidazolium)–Cucurbit[8]uril Complexes for Binding and Sensing Aromatic Compounds in Aqueous Solution

“…[5] Primary, secondary, tertiary and aryl groups have been installed as Nsubstituents, and the C2 position can be functionalized with aryl or heterocyclic groups, resulting in an extensive repertoire of molecules. [6] BBIs are also chemically and thermally stable with decomposition temperatures typically between 270-340 8C.…”

Synthesis of tetracationic organic salt from 4,4'-bipyridine

“…This is due to the potential to change their structural features simply by: varying the nature of the cation and/or the anion; tuning them by introducing small structural changes in the constituting ions, or of the spacers separating them provides the opportunity to obtain materials with sets of desired properties suitable for different applications. They have been applied as a chemical anchorage on a solid support [10], starting materials for the synthesis of molecular devices [11,12], reaction media or catalysts, immobilization of catalysts [9], reaction media for high-temperature organic reactions [13,14], catalysts [15], receptors for anion recognition [16], low-molecular-weight gelators [17], fluorescent organic salts [18,19], energetic materials [20,21], for use in the preparation of solid films for organic electronic applications [22] and electrowetting materials [23]. Heteromolecules including imidazole, 1,10-phenanthroline, pyridine and others have been used as the starting materials for the synthesis of polycationic organic salts.…”