Aza‐BODIPY Derivatives: Enhanced Quantum Yields of Triplet Excited States and the Generation of Singlet Oxygen and their Role as Facile Sustainable Photooxygenation Catalysts

Abstract

A new series of aza-BODIPY derivatives (4 a-4 c, 5 a,c, and 6 b,c) were synthesized and their excited-state properties, such as their triplet excited state and the yield of singlet-oxygen generation, were tuned by substituting with heavy atoms, such as bromine and iodine. The effect of substitution has been studied in detail by varying the position of halogenation. The core-substituted dyes showed high yields of the triplet excited state and high efficiencies of singlet-oxygen generation when compared to the peripheral-substituted systems. The dye 6 c, which was substituted with six iodine atoms on the core and peripheral phenyl ring, showed the highest quantum yields of the triplet excited state (Φ(T) =0.86) and of the efficiency of singlet-oxygen generation (Φ(Δ) =0.80). Interestingly, these dyes were highly efficient as photooxygenation catalysts under artificial light, as well as under normal sunlight conditions. The uniqueness of these aza-BODIPY systems is that they are stable under irradiation conditions, possess strong red-light absorption (620-680 nm), exhibit high yields of singlet-oxygen generation, and act as efficient and sustainable catalysts for photooxygenation reactions.

The effect of heavy atom to two photon absorption properties and intersystem crossing mechanism in aza-boron-dipyrromethene compounds

“…Thus 5a can be used as triplet photosensitizer for photosensitizing of singlet oxygen ( 1 O 2 ). This theoretical prediction is in agreement with the experimental results [1,47].…”

Visible‐Light Photoactive, Highly Efficient Triplet Sensitizers Based on Iodinated Aza‐BODIPYs: Synthesis, Photophysics and Redox Properties

“…Figure 8p resents, for comparison, the structures, triplet state properties and singlet oxygen formation quantum yields of all halogenated aza-BODIPYs reportedu ntil 2017. [35,41,64,65] We demonstrated that the iodinated aza-BODIPYs 5-8,i n contrastt ot he non-iodinated counterparts 1-4,p roduce highly populated triplet state upon excitation, as evidenced by the observation of transient absorption spectra and lack of room-temperature emission from the singlet excited state (S 1 !S 0 ). In addition, iodinated aza-BODIPYs 5-8 efficiently harvest visible light, as evidenced by their relatively high molar absorption coefficients (e), viz.…”

Boron chemistry in a new light

“…54 Those bearing six heavy atoms were particularly effective. As presented in Scheme 23, one of them was tested for the photooxidation of 1-naphthol into 1,4-naphthoquinone under normal sunlight conditions using acetonitrile as the solvent and with a continuous stream of oxygen.…”