*3.6. Fluorescent Properties Studies*

Figure 12 shows the change in the fluorescent properties of complexes I and II as the corresponding dimers and oligomers were formed from them. The distinguishing feature of the presented spectra was an additional peak in the region of 620–625 nm as the corresponding porphyrin arrays with different numbers of tetrapyrrole chromophores (n = 2, 6) were formed from the porphyrin monomers (complexes I and II). Such a peak probably appeared because the porphyrin dimers and oligomers formed during the chelation had an additional energy level, enabling an emitting transition to the ground state.

**Figure 12.** Fluorescence spectra of the studied systems with different concentration ratios of the reagents, λex = 416 nm (I-(**a**), II-(**b**)).

Strong quenching of the fluorescence (Figure 11) of complexes I and II in comparison with bis-hydroxy-5,10,15,20-tetra-(4-sulfonatophenyl)porphyrin-Sn(IV) (III), according to the literature data [62,63] and the results of our own studies [64,65], is caused by the interaction of the closely spaced aromatic systems of the ligand and porphyrin macrocycle (in complex I, the inclination angle of the axial ligand aromatic part to the porphyrin plane was31◦, while in complex II, it was 50◦). The results of the quantum chemical calculations show (Figure 2, Table 1) that as dimeric structures were formed, the inclination angle of the phenolate fragment of the ligands relative to the porphyrin plane increased (the angle became close to 90◦). The functional groups involved in the chelation with Cu2+ cations in the dimeric structures were located at the maximum possible distance from the porphyrin plane. It is logical to assume that the structural changes accompanying the formation of dimeric and oligomeric systems weakened the mutual influence of the aromatic systems of the ligand and macrocycles in them. This is in good agreement with the data presented in Figure 13. In the case of complex I, the quantum yield of the systems formed at different ratios of the reagents (1:1 or 1:5) increased by about two-fold. In the case of complex II, at a 1:5 molar ratio of the reagents, the quantum yield of fluorescence increased by about fourfold. The difference in the quantum yields of the dimeric and oligomeric systems obtained on the basis of complexes I and II could probably be explained by the different sizes of the axial ligands in the corresponding complexes. The importance of spatial effects was confirmed by the data in Tabl. 1, according to which the distance between the porphyrin fragments in the I-Cu-I and II-Cu-II dimers differed significantly and amounted to 21.3 and 17.6 Å, respectively.

It should be also noted that some of the products of reaction (1) precipitated. It is logical to assume that the polymer products of the reaction of the Cu2+ cation chelate complex formation with the studied axial complexes of Sn(IV)-porphyrin were precipitated. Currently, our laboratory is conducting research related to the establishment of their structure and properties. According to the preliminary studies, these porphyrin polymers are characterized by high porosity and capacity to selectively adsorb organic solvent molecules. This suggests that coordination polymers of this type could be promising

"size-responsive" materials (i.e., capable of separating, storing, and transporting aggressive, toxic, or explosive chemical species of different natures).

**Figure 13.** (**a**) Fluorescence quantum yields of complexes III and I and products of their interaction with Cu2+ depending on the concentration ratio of the reagents; (**b**) fluorescence quantum yields of complexes III and II and products of their interaction with Cu2+ depending on the concentration ratio of the reagents.
