The optical and electrochemical properties are compared for aza-BODIPY dyes that differ by virtue of the substituents at 1,7- and 3,5-positions of the aza-BODIPY backbone.
As eries of novel iodinated NO 2 -substituted azaBODIPYs have been synthesized and characterized.H ighly desirable photophysical and photochemical properties were induced in NO 2 -substituted aza-BODIPYs by iodinationo ft he pyrrole rings. In particular, highv alues of singlet oxygen quantum yields (F D )r anging from 0.79 to 0.85 were measured. The photooxygenation process proceeds via aT ype II mechanism under the experimental conditions applied. The compounds studied exhibited an absorption band within the so-called "therapeutic window", with l max located between 645 nm to 672 nm. They were non-fluorescent at room temperature with excited singlet-state lifetimes within the picosecond range as measured by femtosecond transient absorption. Nanosecond laser flash photolysis experiments revealed T 1 !T n absorption spanning from ca. 400 nm to ca. 500 nm and allowedd etermination of the triplet-state lifetimes. The estimated triplet lifetimes (t T )i nd eaerated acetonitrile ranged between 2.74 msa nd 3.50 ms. As estimated by CV/DPV measurements, all iodinateda za-BODIPYs studied exhibited one irreversible oxidation and two quasireversible reductions processes. Estimation of the E HOMO gave the value of À6.06 to À6.26 eV while the E LUMO was found to be located at ca. À4.6 eV.T hermogravimetric (TGA) analysis revealed that iodinated aza-BODIPYs weres table up to approximately 300 8C. All compounds studied exhibit high photostability in toluene solution.
We report herein synthesis of four novel nitro‐substituted aza‐BODIPY (boron‐dipyrromethene) ligands. Two methods are proposed and compared for the synthesis of aza‐BODIPY. Direct conversion of 1,3‐diaryl‐4‐nitrobutan‐1‐ones into aza‐dipyrromethenes usually gives higher reaction yields, however, this method depends on the substitution pattern of the substrate. An efficient synthesis of four 2,4‐diarylpyrroles and four 2,4‐diaryl‐5‐nitrosopyrroles was achieved. Both 2,4‐diarylpyrroles and their nitroso derivatives served as building blocks for the synthesis of aza‐BODIPY. The compounds studied exhibit a broad absorption band from around 500 nm to 700 nm, with λmax located at approximately 620 nm. Differential pulse voltammetry (DPV) was used to study the frontier orbital energy levels. Depending on the substitution pattern, three to four reduction peaks were detected. The value of the first reduction potential (Ered1) and, as a result of it, the value of the ELUMO remained relatively constant across all aza‐BODIPYs studied. However, the value of the first oxidation potential (Eox1), the number of oxidation peaks, the EHOMO, and the electrochemical gap (Eg) were sensitive to the substitution pattern on the ligand. Thermogravimetric (TGA) analysis revealed that the aza‐BODIPYs studied were stable up to approximately 260 °C. All compounds studied exhibited extremely high photostability in THF solution. DFT analysis showed that substitution of the phenyl rings with the NO2 group resulted in the lowering of the energies of both frontiers orbitals and narrowing of the HOMO–LUMO energy gap.
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