Singlet state exciplex formation of phenazine with some aromatic amines

Indirect consequences of exciplex states on the phosphorescence lifetime of phenazine-based 1,2,3-triazole luminescent probes

Exciplex formation, and delayed fluorescence and phosphorescence interplay interactions were investigated in phenazine derivative solutions at room temperature.

Monooxygenation of an appended phenol in a model system of tyrosinase: implications on the enzymatic reaction mechanism

A new model system of tyrosinase was established that performs an ortho-hydroxylation of the appended phenol in the absence of base.

pH-induced changes in electronic absorption and fluorescence spectra of phenazine derivatives

The visible electronic absorption and fluorescence spectra as well as fluorescence polarization degrees of imidazo-[4,5-d]-phenazine (F1), 2-methylimidazo-[4,5-d]-phenazine (F2), 2-trifluoridemethylimidazo-[4,5-d]-phenazine (F3), 1,2,3-triazole-[4,5-d]-phenazine (F4) and their glycosides, imidazo-[4,5-d]-phenazine-N1-beta-D-ribofuranoside (F1rib), 1,2,3-triazole-[4,5-d]-phenazine-N1-beta-D-glucopyranoside (F4gl), were investigated in aqueous buffered solutions over the pH range of 0-12, where the spectral transformations were found to be reversible. The effects of protonation and deprotonation on spectral properties of these dyes were studied. We have determined the ranges of pH, where individual ionic species are predominant. In aqueous buffered solutions the fluorescence was found only for neutral species of F1, F1rib, F2, and F4gl dyes, whereas for the ionic forms of these dyes, as well as for F3 and F4 ones, the fluorescence has not been detected. The concentrational deprotonation pKa values were evaluated from experimental data. It was shown that donor-acceptor properties of the substituent group in the second position of the pentagonal ring substantially affect the values of the deprotonation constants and the character of protonation for chromophore. The substitution of a hydrogen atom in the NH-group by the sugar residue blocks the formation of the anionic species, and results in enhancement of the dye emission intensity. The steep emission dependence for F1 and F1rib over pH range of 0-7 with intensities ratio of IpH 7/IpH 1=60 allows us to propose them as possible indicator dyes in luminescence based pH sensors for investigation of processes accompanied by acidification, e.g. as gastric pH-sensors. A comparative analysis of the studied dyes has shown that F4gl is the most promising compound to be used as a fluorescent probe for investigation of molecular hybridization of nucleic acids.

Magnetic Field Effect on Photoinduced Electron Transfer between Dibenzo[a,c]phenazine and Different Amines in Acetonitrile−Water Mixture

Unlike the simple phenazine (PZ) molecule, one of its derivatives, dibenzo[a,c]phenazine (DBPZ) forms a charge-transfer complex in the triplet state (3ECT) with different amines, e.g., N,N-dimethylaniline (DMA), 4,4'-bis(dimethylamino)diphenylmethane (DMDPM), and triethylamine (TEA). Formation of the 3ECT and radical ion pairs (RIPs) due to electron transfer is identified by laser flash photolysis. The RIPs are much more abundant in the cases of DMA and DMDPM rather than in TEA. Interestingly, a prominent magnetic field effect (MFE) is observed in both the cases of 3ECT and RIPs in homogeneous acetonitrile-water (MeCN/H2O) mixtures. This rare observation of the 3ECT and MFE in non-viscous medium could be explained by considering the extended planar structure of DBPZ and inter-radical hydrogen bonding, mediated by the intervening water molecules. The magnetic field behavior is consistent with the hyperfine mechanism; however, the low B1/2 value for DBPZ-TEA system is ascribed to fast electron exchange due to the close proximity of the corresponding radical ions.

Interaction of phenazine with water and DNA bases

The fluorescence spectrum of aqueous phenazine (PZ), an N-heterocyclic compound, shows some interesting features that indicate the formation of PZ-water complex in the excited state. Two types of complexes are postulated; Type I, formed by the association of water molecule with one of the nitrogen of PZ and Type II, formed by the association of water molecules with both the nitrogen of PZ. In addition, PZ also interacts with the DNA bases, adenine and thymine and the corresponding nucleosides, adenosine and thymidine. Fluorescence and laser flash photolysis studies indicate that the mode of interaction may be photoinduced electron transfer.

Exploring the Extent of Magnetic Field Effect on Intermolecular Photoinduced Electron Transfer in Different Organized Assemblies

Magnetic field effect (MFE) on the photoinduced electron transfer (PET) between phenazine (PZ) and the amines, N,N-dimethylaniline , N,N-diethylaniline, 4,4'-bis(dimethylamino)diphenylmethane (DMDPM), and triethylamine, has been studied in micelles, reverse micelles, and small unilamellar vesicles (SUVs) with a view to understand the effect of spatial location of the donor and acceptor moieties on the magnetic field behavior. The structure of the assembly is found to influence greatly the PET dynamics and hence the MFE of all the systems studied. The magnetic field behavior in micelles is consistent with the hyperfine mechanism, but high B(1/2) values have been obtained which have been ascribed to hopping and lifetime broadening. The variation of MFE with W(0), in reverse micelles, proves yet again that the MFE maximizes at an optimum separation distance between the acceptor and donor. This is the first example of such behavior for intermolecular PET in heterogeneous medium. We have also reported for the first time MFE on intermolecular PET in SUVs. In this case, the PZ-DMDPM system responds most appreciably to an external field compared to the other acceptor-donor systems because it is appropriately positioned in the bilayer. The differential behavior of the amines has been discussed in terms of their confinement in different zones of the organized assemblies depending on their bulk, hydrophobic, and electrostatic effects.

Time-resolved electron paramagnetic resonance of the lowest excited triplet state of phenazinium cation

Time-resolved and steady-state electron paramagnetic resonance (EPR) spectra have been observed for the lowest excited triplet (T(1)) states of phenazine (Phz) and its singly protonated cation (phenazinium) in sulfuric acid-ethanol mixtures at 77K. The single protonation appears to have little effect on the anisotropic sublevel populating rates of the T(1) state of phenazine. However, the zero-field splitting (ZFS) parameter D decreases on the protonation, reflecting the increase of delocalization of the two unpaired electrons. The sublevel preferentially populated by intersystem crossing (ISC) is T(y) in both phenazine and phenazinium (the y-axis is parallel to the in-plane long axis). From the analysis of the observed anisotropy in the ISC rates and the semi empirical molecular orbital calculations of the ZFS parameters, we concluded that the T(1) state of phenazinium is the (3)A(1)(pipi*) state.