Specific emission and quenching of photoexcited tetraphenylporphyrin derivatives incorporated in a Nafion film

Synthesis of novel dimeric subphthalocyanines via azide-alkyne Huisgen 1,3-dipolar cycloaddition and palladiumcatalyzed Glaser–Hay coupling reactions

In this study, the monomeric subphthalocyanines bearing azido (2) and terminal ethynyl (3) groups were synthesized. These subphthalocyanines were converted to their dimeric derivatives using azide-alkyne Huisgen cycloaddition and palladium-catalyzed Glaser–Hay coupling reactions subphthalocyanine (4) and (5), respectively. The novel subphthalocyanines were fully characterized by elemental analysis and general spectroscopic methods such as MALDI-TOF mass, FT-IR, UV-vis and [Formula: see text]H-NMR. All synthesized subphthalocyanines showed quite good solubility in the most of common organic solvents. The fluorescence measurements were conducted for these subphthalocyanines to estimate their fluorescence quantum yields. The singlet oxygen generation abilities were also examined to investigate their photosensitizer properties.

Regulation of the Extent and Dynamics of Excited-State Proton Transfer in 2-(2‘-Pyridyl)benzimidazole in Nafion Membranes by Cation Exchange

The effect of the microenvironment of a Nafion membrane on the excited-state proton transfer (ESPT) of 2-(2'-pyridyl)benzimidazole (2PBI) has been investigated by steady-state and time-resolved fluorescence spectroscopy. The mechanism of the ESPT is found to depend remarkably on the water content of the membrane. In the protonated form of the membrane, ESPT is found to involve the dicationic (D) form of the fluorophore, whereas in cation-exchanged membranes, it is found to involve the monocation (C). The change in the mechanism and extent of ESPT in cation-exchanged membranes can be explained by considering dehydration of the membrane as well as the less acidic environment around the 2PBI molecules. The slow dynamics is found to result from two factors, namely, slow and incomplete solvation of the transition state, leading to a slowing down of the proton-transfer process, and a slow solvation of the polar tautomeric excited state.

Porphyrin assembly on beta-cyclodextrin for selective sensing and detection of a zinc ion based on the dual emission fluorescence ratio

In the present paper, a new cyclodextrin/porphyrin supramolecular sensitizer for zinc ion has been proposed based on the porphyrin dual fluorescence emission ratio. In aqueous solution, meso-tetraphenylporphyrin shows weak fluorescence, while in the presence of alkylated beta-cyclodextrin, it exhibits significant fluorescence enhancement by forming a cyclodextrin/porphyrin inclusion complex. Furthermore, the formation of a supramolecular complex causes a remarkable increase of the porphyrin metalation rate following the porphyrin fluorescence emission changes at two different emission wavelengths. The fluorescence emission of tetraphenylporphyrin at 656-nm bands decreases while that at 606 nm increases upon zinc ion interaction. Thus, the inclusion complex can behave as a ratiometric fluorescent sensor. Theoretically derivative equations for fluorescent ratiometry have been proposed for the first time. The feasibility of the proposed method is demonstrated by the performance of fluorometric detection of zinc ion. With the optimum conditions described, zinc ion in aqueous solution can be determined from 5.0 x 10(-7) to 2.5 x 10(-4) M. As the porphyrin electronic absorption and fluorescence emission are located in the visible range, and the fluorescence changes upon zinc ion interaction show high selectivity over biologically relevant cations, the inclusion complex could be used for biomedical application.

Emission of thioflavin T and its off-on control in polymer membranes

The absorption and emission spectral properties of thioflavin T (TFT+) in Nafion (Nf) and cellulose matrices have been studied. Formation of the emittive dimer is observed in both matrices. The monomer TFT+ emission is blueshifted in Nafion membrane (Nf), whereas it is red-shifted in cellulose membrane when compared with the emission in aqueous solution. The dimer emission of TFT+ in the Na+-Nf membrane undergoes off-on switching with acids and alkalis. The TFT+ molecule undergoes protonation in the H+-Nf and the protonated dye is fluorescent. The dimer emission of TFT+ is not observed in the dry H+-Nf membrane because of the protonation of the TFT+ molecule. The diffusion coefficient and the free energy of hydrophobic interaction for the TFT+ molecule in the Nf membrane are calculated. The TFT+ molecule experiences hydrophobic and electrostatic interactions in the Nf matrix, whereas it experiences a polar environment in the cellulose membrane. The 3D emission spectral studies support the formation of the emittive dimer in both Nf and cellulose matrices.