A Singlet Oxygen Photogeneration and Luminescence Study of Unsymmetrically Substituted Mesoporphyrinic Compounds

Abstract

This paper deals with a series of new unsymmetrically substituted mesoporphyrins: 5-(2-hydroxyphenyl)-10,15,20-tris-phenyl-21,23-H-porphyrin (TPPOHO), 5-(3-hydroxyphenyl)-10,15,20-tris-phenyl-21,23-H-porphyrin (TPPOHM), 5-(4-hydroxyphenyl)-10,15,20-tris-phenyl-21,23-H-porphyrin (TPPOHP), 5-(2-hydroxyphenyl)-10,15,20-tris-butyl-21,23-H-porphyrin (TBPOHO), and their parent nonsubstituted compounds, respectively, 5,10,15,20-tetrakis-phenyl-21,23-H-porphyrin (TPP) and 5,10,15,20-tetrakis-butyl-21,23-H-porphyrin (TBP). Several photophysical studies were carried out to access the influence of the unsymmetrical substitution at the porphyrinic macrocycle on porthyrin's photophysical properties, especially porthyrin's efficiency as singlet oxygen sensitizers. The quantum yields of singlet oxygen generation were determined in benzene (ΦΔ(TPP) = 0.66 ± 0.05;ΦΔ(TPPOHO) = 0.69 ± 0.04;ΦΔ(TPPOHM) = 0.62 ± 0.04;ΦΔ(TPPOHP) = 0.73 ± 0.03;ΦΔ(TBP) = 0.76 ± 0.03;ΦΔ(TBPOHO) = 0.73 ± 0.02) using the 5,10,15,20-tetraphenyl-21,23-H-porphine (ΦΔ(TPP) = 0.66) and Phenazine (ΦΔ(Phz) = 0.83) as reference compounds. Their fluorescence quantum yields were found to be (Φf(TPPOHO) = 0.10 ± 0.04;Φf(TPPOHM) = 0.09 ± 0.03;Φf(TPPOHP) = 0.13 ± 0.02;Φf(TBP) = 0.08 ± 0.03 andΦf(TBPOHO) = 0.08 ± 0.02 using 5,10,15,20-tetraphenyl-21,23-H-porphine as referenceΦf(TPP) = 0.13). Singlet state lifetimes were also determined in the same solvent. All the porphyrins presented very similar fluorescence lifetimes (mean values ofτS(withO2, air equilibrated) = 9.6 ± 0.3 nanoseconds and (withoutO2, argon purged) = 10.1 ± 0.6 nanoseconds, resp.). The phosphorescence emission was found to be negligible for this series of unsymmetrically substituted mesoporphyrins, but an E-type, thermally activated, delayed fluorescence process was proved to occur at room temperature.

Studies on the Synthesis, Photophysical and Biological Evaluation of Some Unsymmetrical Meso-Tetrasubstituted Phenyl Porphyrins

“…The changes observed in the spectral behavior were in agreement with our previous results obtained for other unsymmetrical porphyrins [ 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ]. Comparison of the absorption spectral parameters indicated that they were not significantly affected either by the type of peripheral substituents of the porphyrinic core, or by environmental polarity.…”

“…The unsymmetrical compounds were synthesized according the methods proposed by Adler et al [ 30 ] and Little et al [ 31 ] and adapted by the authors [ 21 , 24 , 25 , 26 , 27 , 28 , 29 ]. The synthesis reactions, as described at Section 3.2 and Section 3.3 ., were repeated several times with similar results, proving good reproducibility.…”

“…Therefore, changes in the molecular architecture of porphyrins by introducing polar and nonpolar substituients [ 14 , 15 ] or metallic ions [ 15 ] can improve their photophysical characteristics and pharmacological efficacy. Consequently, as part of our ongoing research on obtaining unsymmetrical meso -tetrasubstituted phenyl porphyrins [ 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ], we designed and synthesized three new unsymmetrical meso -tetrasubstituted phenyl porphyrins whose general structure is presented in Figure 1 : 5-(4-hydroxy-3-methoxyphenyl)-10,15,20- tris -(4-acetoxy-3-methoxyphenyl)porphyrin ( P2.2 ), Zn(II)-5-(4-hydroxy-3-methoxyphenyl)-10,15,20- tris -(4-acetoxy-3-methoxyphenyl)porphyrin ( Zn(II)2.2 ), Cu(II)-5-(4-hydroxy-3-methoxyphenyl)-10,15,20- tris -(4-acetoxy-3-methoxyphenyl)porphyrin ( Cu(II)2.2 ). These compounds are intended to be developed as theranostic agents for photodynamic therapy (PDT) in cancer.…”

Physicochemical properties of potential porphyrin photosensitizers for photodynamic therapy

“…According to literature data, the fluorescence lifetime of porphyrins can range from picoseconds to several nanoseconds [31][32][33]. In published literature, the fluorescence lifetime of TPP in DMF and benzene is 10.6 ns and 9.7 ns, respectively [34,35]. A summary of the determined fluorescence lifetimes of the porphyrins with v 2 values is presented in Table 2.…”

Magnesium porphyrazine with peripheral methyl (3,5-dibromophenylmethyl)amino groups – synthesis and optical properties

“…The facts that the fluorescence emission is not observed as well as the values of singlet oxygen generation are very low, indicate that both fluorescence is not the main radiative deactivation pathway to the ground state as well as the triplet state population is not significant enough. It is known that the more significant the population of the first triplet state is, the higher the probability of the energy transfer from the photosensitizer to the oxygen with the consequent production of singlet oxygen is observed [28]. Usually, the presence of heavy atoms, such as bromine atoms, increases the efficiency of intersystem crossing to the triplet state and yields of singlet oxygen generation.…”