Studies of photoinduced electron transfer and energy migration in a conjugated polymer system for fluorescence "turn-on" chemosensor applications

Photo- and Sono-Active Food Colorants Inactivating Bacteria

Food colorants are commonly used as excipients in pharmaceutical and nutraceutical fields, but they have a wide range of other potential applications, for instance, as cytotoxic drugs or mediators of physical antimicrobial treatments. The photodynamic antibacterial activity of several edible food colorants is reported here, including E127, E129, E124, E122, E133, and E150a, alongside Rhein, a natural lipophilic antibacterial and anticancer compound found in medicinal plants. Minimal inhibitory concentration (MIC) values for S. aureus and E. coli showed that E127 and Rhein were effective against both bacteria, while other colorants exhibited low activity against E. coli. In some cases, dark pre-incubation of the colorants with Gram-positive S. aureus increased their photodynamic activity. Adding Rhein to E127 increased the photodynamic activity of the latter in a supportive mode. Optional sensing mechanism pathways of combined E127/Rhein action were suggested. The antibacterial activity of the studied colorants can be ranged as follows: E127/Rhein >> E127 >> E150a > E122 > E124 >> E129 ≈ E133. E127 was also found to exhibit photodynamic properties. Short ultrasonic treatment before illumination caused intensification of E127 photodynamic activity against E. coli when applied alone and especially in combination with Rhein. Food colorants exhibiting photo- and sonodynamic properties may have good potential in food preservation.

Pentiptycene-Derived Fluorescence Turn-Off Polymer Chemosensor for Copper(II) Cation with High Selectivity and Sensitivity

Fluorescent conjugated polymers (FCPs) have been explored for selective detection of metal cations with ultra-sensitivity in environmental and biological systems. Herein, a new FCP sensor, tmeda-PPpETE (poly[(pentiptycene ethynylene)-alt-(thienylene ethynylene)] with a N,N,N′-trimethylethylenediamino receptor), has been designed and synthesized via Sonogashira cross-coupling reaction with the goal of improving solid state polymer sensor development. The polymer was found to be emissive at λ_max ~ 459 nm under UV radiation with a quantum yield of 0.119 at room temperature in THF solution. By incorporating diamino receptors and pentiptycene groups into the poly[(phenylene ethynylene)-(thiophene ethynylene)] (PPETE) backbone, the polymer showed an improved turn-off response towards copper(II) cation, with more than 99% quenching in fluorescence emission. It is capable of discriminating copper(II) cation from sixteen common cations, with a detection limit of 16.5 nM (1.04 ppb).

A ruthenium(iii) complex derived from N,N′-bis(salicylidene)ethylenediamine as a chemosensor for the selective recognition of acetate and its interaction with cells for bio-imaging: experimental and theoretical studies

A ruthenium(iii) complex ofN,N′-bis(salicylidene)ethylenediamine (L¹) was used as chemosensor for the recognition of acetate in cells for bio-imaging.

Construction of response patterns for metal cations by using a fluorescent conjugated polymer sensor array from parallel combinatorial synthesis

Pattern-based strategy is an emerging field of interest for effective sensing applications. Seven different conjugated polymers from combinatorial synthesis were combined into a sensor array, and seven metal cations were selected as representative analytes. The response patterns for each cation were constructed by collecting the individual fluorescence responses from seven polymers in the array. Each ion owns a characteristic pattern. Some of them have similar modes of response with subtle differences, while some patterns are distinctively different. The family/period the metal cations belong to and the charges/electronic configurations they possess may account for such similarity/difference in the pattern.

METAL-CONTAINING CONJUGATED POLYMERS AS FLUORESCENT CHEMOSENSORS IN THE DETECTION OF TOXICANTS

Fluorescent conjugated polymers have received a great deal of recent interest due to their ability to act as chemosensors to detect various chemical species in both environmental and biological systems with sensitivity and selectivity. Examples from the literature include polymer chemosensors that operate on either fluorescence "turn-on" or "turn-off" as mechanisms of sensor response. These responses can be related to either photoinduced electron transfer or electronic energy transfer mechanisms. Recently, a series of metal-containing polymers or metallopolymers have been explored by various research groups for their use as chemosensors. In many cases, these metallopolymers have been shown to be more sensitive and selective for specific chemical species. This review focuses on fluorescent conjugated polymers as chemosensors, with a specific concentration on recent advances in metallopolymer chemosensors.

Donor-acceptor substituted phenylethynyltriphenylenes - excited state intramolecular charge transfer, solvatochromic absorption and fluorescence emission

Several 2-(phenylethynyl)triphenylene derivatives bearing electron donor and acceptor substituents on the phenyl rings have been synthesized. The absorption and fluorescence emission properties of these molecules have been studied in solvents of different polarity. For a given derivative, solvent polarity had minimal effect on the absorption maxima. However, for a given solvent the absorption maxima red shifted with increasing conjugation of the substituent. The fluorescence emission of these derivatives was very sensitive to solvent polarity. In the presence of strongly electron withdrawing (-CN) and strongly electron donating (-NMe₂) substituents large Stokes shifts (up to 130 nm, 7828 cm⁻¹) were observed in DMSO. In the presence of carbonyl substituents (-COMe and -COPh), the largest Stokes shift (140 nm, 8163 cm⁻¹) was observed in ethanol. Linear correlation was observed for the Stokes shifts in a Lippert-Mataga plot. Linear correlation of Stokes shift was also observed with E(T)(30) scale for protic and aprotic solvents but with different slopes. These results indicate that the fluorescence emission arises from excited state intramolecular charge transfer in these molecules where the triphenylene chromophore acts either as a donor or as an acceptor depending upon the nature of the substituent on the phenyl ring. HOMO-LUMO energy gaps have been estimated from the electrochemical and spectral data for these derivatives. The HOMO and LUMO surfaces were obtained from DFT calculations.

Fluorescent “light-up” bioprobes based on tetraphenylethylene derivatives with aggregation-induced emission characteristics

Aggregation in poor solvents and complexation with calf thymus DNA and bovine serum albumin turn "on" the fluorescence of tetraphenylethylene derivatives, due to the restriction of intra-molecular rotations of the dyes in the aggregates and complexes.