Spectroscopic and quantum chemical study of phthalocyanines with 1,4,7-trioxanonyl moieties

The spectral properties of new active in PDT anticancer and antiviral dye - 1,4,8,11,15,18,22,25-octakis(1,4,7-trioxanonyl)phthalocyanine and its metal complexes were investigated in terms of their spectroscopic properties. Three quantum chemical restricted (DFT), unrestricted (UDFT) and time-dependent (TD-DFT) models were applied to explain phenomena observed in the experimental data. The experimental UV–Vis-near-IR spectra were compared with the time-dependent density functional theory model PCM/ωB97X-D/6-31+G(d,p). The theoretical model revealed excellent compliance with measurements for magnesium complex and free metal ion phthalocyanine (relative errors were less than 5%). All observed electronic UV–Vis transitions were π→π* type. The Q band, which is crucial for photodynamic activity, presented HOMO to LUMO and HOMO to LUMO+1 character. The excited-state dynamics, including fluorescence lifetimes of studied phthalocyanines, were analyzed using the Time-Correlated Single Photon Counting (TCSPC) technique in DMF and DMSO. It was found that the fluorescence lifetimes measured for metallated phthalocyanines in DMF and DMSO are very similar, thus indicating their weak interaction with solvents. The fluorescence decays were associated with the type of metal-phthalocyanine complex. Moreover, metal-free phthalocyanine showed a stronger tendency to form aggregates in DMF and DMSO than it was observed for its metal ion complexes. The FTIR (400–4000 cm−1) and Raman (50–1600 cm−1) spectra were recorded, and the obtained data were applied in the quantum chemical study. The UB3LYP/6-31G(d,p) model applied for cobalt(II) and manganese(III) complexes allowed to assign the essential signals obtained in the computational study to these observed in FTIR and Raman experiments.