Neutral and cationic pyridylbutadienes: solvatochromism and fluorescence response with sodium cholate

Abstract

Neutral and cationic diarylbutadienes with pyridine and pyridinium groups as electron acceptors with dimethylamine and diphenylamine as electron donors were synthesized. The absorption and emission properties of these dienes were investigated in homogeneous organic solvents and in sodium cholate media. In strongly polar solvents, both neutral and cationic fluorophores exhibit a bathochromic shift of emission characteristics of intramolecular charge transfer (ICT) excited states. The presence of a strongly electron withdrawing pyridinium group induces large absorption (∼480 nm) and emission wavelength shifts (near ∼680 nm) in polar solvents. This solvatochromic behavior is utilized as a tool to examine the fluorophore-sodium cholate interaction. Significant hypsochromic emission shifts (up to ∼66 nm) and concomitant intensity enhancement (up to 32-fold) are seen for these fluorophores in the presence of increasing concentrations of sodium cholate. Fluorescence lifetime measurements reveal biexponential decay patterns indicating the binding of molecules in distinct cholate environments.

Donor-Acceptor Conjugated System: A Neutral Hydrophobic Fluorescence Probe

“…In general, donor-acceptor substituted diphenyl ethenes and dienes show solvent dependent absorption and fluorescence properties. Some of the molecules exhibit dual fluorescence emission, which is highly dependent upon the local environment and substituent present on the molecule [36][37][38][39][40][41]. For example, diarylethenes bearing donor group, methoxy and amine or acceptor group, cyano and nitro show fluorescence emission from their locally excited state (LE), whereas, in presence of both donor and acceptor substituents, cyano or nitro and methoxy and amine shows solvent polarity-dependent dual fluorescence emission due to LE and intra molecular charge transfer (ICT) states.…”

Push–Pull (Iso)quinoline Chromophores: Synthesis, Photophysical Properties, and Use for White‐Light Emission

“…1,2,3,4,5 Indeed, the photophysical properties of these materials can be easily tuned by environmental stimuli such as polarity, 6,7,8,9 pH, [8][9][10]11 or the presence of metal cations. 12 Six-membered nitrogen heterocycles such as pyridine, 6,13 quinoline 3 or (benzo)diazines [1][2][3][4][5] act as moderate-to-strong electron-withdrawing groups. When protons or metal cations are added the photophysical properties are modified due to the interaction with the electron lone pair of the nitrogen atoms of the heterocycle.…”

Emission and Color Tuning of Cyanostilbenes and White Light Emission

“…17,19−25 Among many known derivatives, there is an active interest toward materials exhibiting unique aggregation-induced emission (AIE or AIEE) for their excellent emissive properties in the solid or aggregated state due to restricted molecular rotations with subsequent reduction of radiationless decay processes. 26−29 α-Cyanostilbenes belongs to one such class of π-conjugated substrates that exhibit this unique emission behavior and were widely utilized for optical and biological applications. 30−35 Cyanostilbenes are considered to be an attractive platform as different chemical entities can be synthetically incorporated in the core structure in the form of the donor (D) or acceptor (A) groups and other functional moieties via routine synthetic procedures.…”

“…Organic materials emitting white light have attracted significant attention for their potential applicability in lighting devices and for efficient energy utilization. , In general, the white light emission is obtained by blending of two or more complementary colors that cover the full spectrum of visible wavelength ranging from 400 to 700 nm. − Traditionally, the white light emission has been achieved with the use of single chromophoric systems, self-assembly, , complexation with macrocyclic hosts, supramolecular gelation , or through the use of natural pigments from vegetable extracts, , and related processes. − A scaffold with suitable electronic push–pull substituents separated by a π-spacer is prevalent in the organic dyes exhibiting strong emission or color characteristics. Such molecular materials with electron-donating and electron-accepting substituents connected through conjugated π-electrons (D−π–A) have been extensively investigated because of their abundant applications for organic electronic and biological applications. ,− Among many known derivatives, there is an active interest toward materials exhibiting unique aggregation-induced emission (AIE or AIEE) for their excellent emissive properties in the solid or aggregated state due to restricted molecular rotations with subsequent reduction of radiationless decay processes. − α-Cyanostilbenes belongs to one such class of π-conjugated substrates that exhibit this unique emission behavior and were widely utilized for optical and biological applications. − Cyanostilbenes are considered to be an attractive platform as different chemical entities can be synthetically incorporated in the core structure in the form of the donor (D) or acceptor (A) groups and other functional moieties via routine synthetic procedures . Self-assemblies, nanostructures, supramolecular complexes, fluorescent probes, sensors, supramolecular materials, and several other functional materials with cyanostilbene core have been investigated by taking advantage of this synthetic tunability. − Previously, derivatives based on tetraphenylethylene, a well-known AIE substrate, is shown to emit white light in the presence of a suitable polymer host or dopant. − …”