Narrow Results

This work is devoted to studying the aggregation effect on the nonlinear optical (NLO) and charge transport (CT) properties of low-symmetry phthalocyanines bearing a cyclotriphosphazene moiety, a monomer, and clamshell-type bis-phthalocyanine. FE-SEM and AFM studies revealed ordered nanoaggregation in these compounds, represented as repeating objects of regular configuration, globules (340–480 nm), which contain small aggregates inside their cavity, similar to smoothed polygons (ca. 40 nm). Such specificity is not characteristic of other functionalized phthalocyanines, which we dealt with earlier. A new spectral method for estimating the aggregation threshold based on the change in extinction with increasing concentration of solutions was also implemented, and the effect of aggregation on optical limiting was demonstrated. The behavior of isomers and rotamers of bis-phthalocyanine in the presence of electric fields of various strengths was investigated with the DFT calculations, and that partially corresponds to the impact of laser radiation on molecules. It was shown that the unusual behavior of the trans-isomer in FF-DFT calculations is the reason for the worsening of the NLO and CT characteristics of bis-phthalocyanine, in which the macrocycles are strapped through a phosphazene spacer. An advanced method of multiparametric analysis has been implemented to evaluate the NLO and CT properties of the dyes in general.

The aggregative state of the Zn(II) tetra-spermine porphyrin derivative, ZnTCPPSpm4, has been investigated in the presence of different buffers at the same pH value: 5K (cacodylate) buffer, phosphate sodium salt buffer, and PBS. The photophysical characterizations (UV-vis, Fluorescence, and RLS) have indicated a precise self-assembly phenomenon depending on the buffered solution used. The porphyrin does not undergo a significant aggregation in 5K buffer, differently from what occurs in phosphate and PBS buffers. Here, the likely specific interaction between the phosphate molecules and spermine pendants leads to spontaneous porphyrin aggregation, as detected by the high fluorescence quenching, enhancement of the RLS signal, and a significant splitting of the porphyrin Soret band. As a result, the current paper aims to highlight the importance of the employed buffer throughout the experimental procedures performed in the presence of porphyrinoids.

In this work, the interaction of metal-free octaethylporphyrin (P) and a Mn(III) octaethylporphyrin chloride (MnP) films with various RNA nucleoside molecules (adenosine [A], cytidine [C], guanosine [G] and uridine [U]) was investigated to elucidate a possible molecular recognition. The porphyrin film-nucleoside interaction took place in solution, which was analyzed to quantify the nucleoside adsorption. The films were investigated by using microscopy and spectroscopic techniques (SEM, AFM, UV-Vis and IR), in addition to the in-plane film conductivity. Experimental results were correlated with DFT calculations to investigate binding energies, separation distances, and adsorption sites, among others. From these results, it was observed that purine bases were preferably adsorbed by the metal-free porphyrin film, while pyrimidine bases were adsorbed on the manganese porphyrin surface. Conductivity results exhibited the highest resistance for the bare metal-free film, but its conductivity increases after nucleoside adsorption, being the purine molecules the most resistive and the pyrimidine molecules the most conductive. In contrast, the Mn porphyrin film showed the highest conductivity, but after nucleoside adsorption, the resistivity increased for purine and pyrimidine bases, being pyrimidines the less conductive. DFT calculations showed binding energies PG>PA>PC>PU and MnPC>MnPG>MnPA>MnPU, which were consistent with experimental findings. In general, the main interactions took place between the porphyrin core and the pentose of the nucleoside, while MnP formed Mn porphyrin-nucleoside arrangements with octahedral geometry. The calculated UV-Vis spectra were in agreement with the experimental plots. From these results, changes in nucleoside adsorption can lead to a selective recognition of nucleoside molecules.