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

Abstract

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.

Facile Synthesis, Triplet‐State Properties, and Electrochemistry of Hexaiodo‐Subphthalocyanine

“…It is well established that the incorporation of certain transition metals (e.g., d 10 Cu I , d 6 Re I , d 4 Re III , d 6 Ru II , d 6 Os II , d 6 Ir III , d 8 Pt II , d 8 Pd II , d 10 Au I , or d 8 Au III ) into organic ligands results in the formation of highly populated triplet states upon electronic excitation . Similarly, the functionalization of an organic molecule with atoms with high atomic numbers, such as I, Br, Ir, Pt, Ru, Os, Pb, Tl, etc., can induce spin–orbit coupling due to the heavy atom effect, thus, facilitating intersystem crossing (ISC) . Finally, efforts have been dedicated to developing heavy‐atom‐free organic triplet photosensitizers with C 60 –chromophore hybrids being an example of the later …”

“…[1,3,20] Similarly,the functionalizationof an organic molecule with atoms with high atomic numbers, such as I, Br,I r, Pt, Ru, Os, Pb, Tl,e tc.,c an induces pin-orbit coupling duet ot he heavy atom effect, thus, facilitating intersystem crossing (ISC). [21][22][23] Finally,e fforts have been dedicated to developing heavy-atom-free organic triplet photosensitizers with C 60 -chromophore hybrids being an exampleo fthe later. [1] Subphthalocyanines( SubPcs), al ower homologues of the better-known phthalocyanines( Pcs), are an interesting class of organic chromophorest hat can be utilized as triplet photosensitizers.…”

Accessing Symmetrical Tetraphenyl‐pyrrole‐2‐yl Squaraines Through an Improved Synthesis of 2,4‐Diphenylpyrrole

“…Soon, a plethora of literature reports accompanied by an overwhelming number of patent applications appeared, pointing to the importance of squaraine dyes in fundamental research and their potential for high‐tech applications . Owing to their advantageous and tunable photophysical properties squaraine dyes have been considered as photosensitizers for photodynamic therapy (PDT) . Due to their high absorption coefficients, tunable bandgaps and bandwidths, tunable electrochemistry, often coupled with resistance to photodegradation and good thermal stability, squaraine dyes have been employed as light harvesting materials in organic photovoltaic cells (OPV) where they served as donor molecules .…”

Near‐Infrared Photoactive Aza‐BODIPY: Thermally Robust and Photostable Photosensitizer and Efficient Electron Donor

“…Owing to their advantageous photophysical properties (triplet lifetimes τ T , triplet state quantum yields Φ T and triplet state energies E T ) combined with tunable singlet oxygen quantum yields (Φ Δ ) and ability to absorb light from the “therapeutic window”, aza‐BODIPYs have been proposed as potential triplet photosensitizers for both anti ‐microbial and anti ‐cancer photodynamic therapy . Furthermore, aza‐BODIPYs were considered as fluorescent chemosensors for the detection of ammonia, cysteine, homocysteine and glutathione in living cells, Hg 2+ , F − , in vivo detection of H 2 S and NO, carbon dioxide, glucose in whole blood and pH‐sensitive sensors . Aza‐BODIPYs have also been tested as photoactive components in photovoltaic devices and nonlinear optical materials …”