Peripheral substitution as a tool for tuning electron-accepting properties of phthalocyanine analogs in intramolecular charge transfer

Abstract

The intramolecular charge transfer (ICT), which is a pathway for excited state relaxation, was studied on the newly synthesized zinc(ii) complexes of tetrapyrazinoporphyrazines bearing one fixed donor (i.e., a dialkylamino substituent). The rest of the peripheral substituents on the core was designed with respect to their different electronic effects (OBu, neopentyl, StBu, COOBu). The photophysical (singlet oxygen and fluorescence quantum yields) and electrochemical (reduction potentials) properties were determined and compared within the series and with compounds that did not contain a donor moiety. The ICT efficiency correlated well with both the electron-deficient character of the core and the Hammett substituent constants σp. The most efficient ICT was observed for the core with the most electron-accepting substituent (COOBu), and the lowest ICT efficiency was detected for the least electron-deficient core (substituted by OBu). Titration of DMSO solutions of target compounds with H2SO4 indicated that basicity of the azomethine bridges was largely influenced by the character of the peripheral substituents while the dialkylamino donor center remained nearly unaffected. Furthermore, protonation of the donor nitrogen caused partial restoration of the fluorescence quantum yield (increase up to 90 times) due to blocking of ICT. The results implied that the ICT efficiency was strongly dependent on the electron-accepting properties of the core whose properties can be readily affected by suitable selection of peripheral substituents.

Metal‐Cation Recognition in Water by a Tetrapyrazinoporphyrazine‐Based Tweezer Receptor

“…[21] These resultsa re in good agreement with our previouss tudy on the structural aspects that influence ICT. [21,23] Specifically, the presence of two nitrogen donors on the TPyzPz core guarantees nearly complete quenching of the excited states, and therefore, the OFF state of the sensors is almost non-fluorescent.…”

New Benzo[h]quinolin-10-ol Derivatives as Co-sensitizers for DSSCs

“…The efficient lifetimes of 1a and 2a are comparable in the same solvent and slightly shorter in DMF (4.24–4.57 ns) than in MeOH (5.56–5.97 ns). The time-resolved data and emission range imply that for dyes 1a and 2a , the ICT character is lessened, and the fluorescence may originate from π→π * excited state because ICT is a competitive relaxation process of the singlet excited state and typically reduces the fluorescence [ 54 ].…”

Photoinactivation of Planktonic and Biofilm Forms of Escherichia coli through the Action of Cationic Zinc(II) Phthalocyanines

“…[30] [b] in M À1 .cm À1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 represents a continuous, non-destructive and real-time method. [13,20,38] In this approach, bioluminescence is directly correlated with viable cells, because only the active cells are able to produce light. [39] However, the light emission of biofilms tends to be lower than in planktonic cells, due to nutrient starvation and oxygen availability, i. e., a reduction in the biofilm light emission may not always correspond to an irreversible inactivation of the cells.…”

“…It has been demonstrated that insertion of amine groups is also a good strategy for quaternization and optimization of Pc photosensitizing abilities [32–34]. The presence of amine groups can induce a red shift effect in the Q‐band of Pc, which could be a major advantage when applying PDI for clinical purposes ,. The cellular localization and preferential binding sites are strongly influenced by the molecular structure as well as the nature, number and distribution of charges on the PS.…”