Near‐Infrared BODIPY‐Acridine Dyads Acting as Heavy‐Atom‐Free Dual‐Functioning Photosensitizers

Abstract

Boron dipyrromethene (BODIPY)d yes represent a particular class within the broad array of potential photosensitizers.T heir highly fluorescent nature opens the door for theragnostic applications,c ombining imaginga nd therapy using as ingle, easily synthesized chromophore. However, near-infrareda bsorption is strongly desired for photodynamic therapy to enhance tissue penetration. Furthermore, singlet oxygen should preferentially be generated without the incorporation of heavy atoms,a st hese often require additional synthetice fforts and/ora fford dark cytotoxicity.S olu-tions for both problemsa re known,b ut have never been successfully combinedi no ne simple BODIPYm aterial. Here, we present as eries of compact BODIPY-acridine dyads, active in the phototherapeutic window and showingb alanced brightness andp hototoxic power.A lthough the donor-acceptor design was envisioned to introduce a charget ransfer state to assist in intersystem crossing, quantum-chemicalc alculations refute this. Furtherp hotophysical investigations suggest the presence of exciplex states and their involvement in singlet oxygen formation.

Bridge control of photophysical properties in benzothiazole-phenoxazine emitters – from thermally activated delayed fluorescence to room temperature phosphorescence

“…The observation of phosphorescence in solution correlates with the high singlet oxygen generation and possibly opens up applications in other fields such as (image-guided) photodynamic therapy. [55][56][57] Altering the p-bridge thus has a drastic effect on the excited/ground-state transition rates governing the emission mechanism, which consequently has a significant impact on the photophysical properties. These results provide further insights into the relationship between the bridging moiety and the photophysical properties of D-p-A type small-molecule emitters and contribute to the future development of applications relying on different types of emission from purely organic molecules.…”

Balancing fluorescence and singlet oxygen formation in push–pull type near-infrared BODIPY photosensitizers

“…4-(9,9-Dimethyl-9,10-dihydroacridin-10-yl)benzaldehyde (4a) 10 : Obtained according to the general Buchwald-Hartwig procedure using 4-bromobenzaldehyde (1.00 g, 5.40 mmol), 9,9-dimethyl-…”

“…1 H NMR (CDCl3, 400 MHz): δ(ppm) = 10.10 (s, 1H), 8.16-8.09 (m, 4H), 7.81-7.77 (m, 2H), 7.51-7.44 (m, 4H), 1.48 (s, 18H). 13 10 Photosensitizers 5a-f (and BODIPY 5H) were synthesized according to the following Knoevenagel-type procedure: 1,3,5,7-Tetramethyl-BODIPY 2 (1 equiv) and aldehyde 4a-f (or benzaldehyde) (4 equiv) were put under inert atmosphere and dissolved in dry N,N-dimethylformamide (60 mL/mmol BODIPY). Glacial acetic acid (1 mL/mmol BODIPY) and piperidine (1 mL/mmol BODIPY) were added to the reaction mixture.…”

“…Because of the small differences in Rf values of the mono-, di-, tri-, and tetra-substituted compounds, further purification was performed via preparative (recycling) size exclusion chromatography (prep-SEC) to obtain BODIPYs 5a-f (and 5H) in pure form. S7 1,7-Dimethyl-3,5-di(4-(9,9-dimethyl-9,10-dihydroacridin-10-yl)styryl)-8-mesityl-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (5a) 10 : Obtained according to the general Knoevenagel-type procedure using 1,3,5,7-tetramethyl-8-mesityl-BODIPY 2 (36.6 mg, 0.1 mmol) and 4-(9,9-dimethyl-9,10-dihydroacridin-10-yl)benzaldehyde (4a) (125.4 mg, 0.4 mmol). The crude product was purified by column chromatography (dichloromethane:hexanes, 30:70), followed by prep-SEC, affording 5a as a dark blue solid with red metallic luster (63.4 mg, 66%).…”

Torsion-Induced Nonradiative Relaxation of the Singlet Excited State of meso-Thienyl Bodipy and Charge Separation, Charge Recombination-Induced Intersystem Crossing in Its Compact Electron Donor/Acceptor Dyads

“…Triplet photosensitizers (PSs) are important in fundamental photochemistry studies as well as in photodynamic therapy (PDT), − photocatalysis, − photovoltaics, − and photon upconversion. − PSs showing strong visible light absorption, efficient intersystem crossing (ISC), and long triplet-state lifetime are highly desired. However, ISC is nonefficient for most aromatic chromophores with large planar π-conjugation systems.…”