The amplified quenching of an anionic conjugated polymer, sulfonated poly(phenylene ethynylene) (PPE-SO 3 − ), by a cationic quencher comprising a boronic acid functionalized benzyl viologen (p-BV 2+ ), has been used to optically detect sugars. In the absence of sugar, a strong polymer/quencher interaction leads to superlinear quenching. In the presence of sugar at pH 7.4, the dicationic viologen derivative forms a neutral zwitterionic species, reducing its ability to complex with and quench the anionic polymer's emission. Addition of sugar to the polymer/ quencher system leads a large increase in the fluorescence intensity (up to 70-fold in one case). Spectral data, quenching parameters, and sugar titration curves are presented and discussed in terms of future development of glucose sensors.

We evaluated the spectral properties of four stilbene derivatives containing the boronic acid group [-B(OH) 2 ]: stilbene-4-boronic acid (STBA), 4′-cyanostilbene-4-boronic acid (CSTBA), 4′methoxystilbene-4-boronic acid (MSTBA), and 4′-(dimethylamino)stilbene-4-boronic acid (DSTBA). The emission spectrum of DSTBA displays a large solvent-polarity dependence showing the formation of a photoinduced charge transfer state (CT). This state is weakly present in MSTBA and not present for CSTBA and STBA for the neutral form of the boronic acid group. These results show the donor withdrawing property of the neutral form of the boronic acid group. At higher pH, the boronic acid group is present in the anionic form [-B(OH) 3 − ], resulting in a change of the configuration around the boron atom from the triangular planar (sp 2 hybridization) to the tetrahedral conformation (sp 3 hybridization). This change induced a blue shift of about 50 nm and an increase of intensity in the emission spectrum of DSTBA because of the loss of the electron-withdrawing properties for the anionic form of the boronic acid group, leading to the loss of the CT effect. The same effect is also observed for MSTBA. In contrast, a red shift of about 35 nm and a decrease of intensity are observed for CSTBA from the neutral to the anionic forms of the boronic acid group. These observations lead to the conclusion that the anionic form of the boronic acid group acts as an electron donor group and a photoinduced CT state can be formed when an electron withdrawing group is present on the fluorophore. The usefulness of this effect for the development of saccharide probes is also demonstrated. After addition of sugar, the emission spectra of DSTBA and MSTBA showed a blue shift and an increase of the intensity. On the other hand, a red shift and a decrease of the intensity are observed in the emission spectra of CSTBA after addition of sugar. A change from the neutral to the anionic form of the boronic acid group is used to explain these changes. These results show that the use of the combination of electron donor or withdrawing groups with the boronic acid group is a new and promising way to develop ratiometric fluorescent probes for glucose and other saccharides.

A detailed analysis of the optical and photophysical properties of 2,2‘:5‘:2‘ ‘:5‘ ‘,2‘ ‘‘-quaterthiophene (QT), 3,3‘ ‘‘-dimethoxy-2,2‘:5‘:2‘ ‘:5‘ ‘,2‘ ‘‘-quaterthiophene (DMOQT), 3,3‘ ‘‘-dimethyl-2,2‘:5‘:2‘ ‘:5‘ ‘,2‘ ‘‘-quaterthiophene (DMQT) and 3‘,4‘ ‘-didecyl-2,2‘:5‘:2‘ ‘:5‘ ‘,2‘ ‘‘-quaterthiophene (DDQT) in various environments is reported. In solution at room temperature, the optical properties of the free molecules are obtained and discussed in terms of the effect of the substitution on the conformation adopted by each derivative in the electronic ground and first excited states. In a tetradecane matrix at 77 K, the optical properties are obtained for the isolated molecules in this rigid medium where the oligothiophenes adopt conformations similar to those found in the solid state. The optical properties of the quaterthiophene derivatives in their aggregated forms and in the solid state are also reported and discussed in terms of the substitutional effect on the intermolecular interactions, which affect the spectral and photophysical properties of the isolated molecules. For the first time, a β,β‘-disubstituted oligothiophene (DMQT) showing an excitonic splitting similar to that obtained for QT is reported. All other substituted oligothiophenes presented show a conformational change, following the aggregation process. This difference is explained by more disordered crystalline forms for DMOQT and DDQT. Theoretical calculations using the ZINDO/S semiempirical method are also performed on the crystalline structure of each derivative in an attempt to correlate the optical properties of these molecules in their aggregated forms and in the solid state with the molecular arrangement found in the crystal.

We report a conformational analysis of several substituted terthiophenes using ab initio calculations performed at the HF/3-21G* level. Geometries of terthiophenes having methoxy substituents in 3,3‘‘ positions (DMOTT), methyl groups in the same positions (DMTT), and ethyl substituents in 3‘,4‘ positions (DETT) are compared with that of the unsubstituted molecule (TT). For all these symmetrical molecules, it is observed that the two dihedral angles are independent of each other. The most stable conformation of TT is found for dihedral angles θ = φ = 147.2°, whereas three maxima are located at 0°, 90°, and 180°. The insertion of methoxy groups in 3,3‘‘ positions favors a more planar conformation with a higher rotational barrier at 90°. This behavior is explained by the electron donor properties of the methoxy groups. By contrast, the addition of two methyl groups at the same positions induces a twisting in the molecule which is caused by the steric hindrance between the methyl substituents and the sulfur atom. The presence of two ethyl groups in 3‘,4‘ positions creates an even stronger steric effect, giving rise to a more twisted conformation for DETT compared to that of DMTT. Absorption and fluorescence spectra of each terthiophene derivative are also reported and are correlated with their respective potential energy surfaces. The more planar molecule (DMOTT) shows a red-shifted absorption band with a higher vibrational resolution and a smaller bandwidth. For more twisted molecules, the blue shift and the bandwidth of the absorption bands increase with twisting while the absorption coefficient decreases. The fluorescence bands, in all molecules, show a better vibrational resolution with a smaller bandwidth compared to their absorption counterparts, while their maximum wavelengths are practically the same, showing that in the first excited singlet state, all molecules relax to a more planar conformation.