Carbazole‐Linked Near‐Infrared Aza‐BODIPY Dyes as Triplet Sensitizers and Photoacoustic Contrast Agents for Deep‐Tissue Imaging

Abstract

Four new N-ethylcarbazole-linked aza-boron-dipyrromethene (aza-BODIPY) dyes (8 a,b and 9 a,b) were synthesized and characterized. The presence of the N-ethylcarbazole moiety shifts their absorption and fluorescence spectra to the near-infrared region, λ≈650-730 nm, of the electromagnetic spectrum. These dyes possess strong molar absorptivity in the range of 3-4×10 m cm with low fluorescence quantum yields. The triplet excited state and singlet oxygen generation of these dyes were enhanced upon iodination at the core position. The core-iodinated dyes 9 a,b showed excellent triplet quantum yields of about 90 and 75 %, with singlet oxygen generation efficiency of about 70 and 60 % relative to that of the parent dyes. Derivatives 8 a,b showed dual absorption profiles, in contrast to dyes 9 a,b, which had the characteristic absorption band of aza-BODIPY dyes. DFT calculations revealed that the electron density was spread over the iodine and dipyrromethene plane of 9 a,b, whereas in 8 a,b the electron density was distributed on the carbazole group and dipyrromethene plane of aza-BODIPY. The uniqueness of these aza-BODIPY systems is that they exhibit efficient triplet-state quantum yields, high singlet oxygen generation yields, and good photostability. Furthermore, the photoacoustic (PA) characteristics of these aza-BODIPY dyes was explored, and efficient PA signals for 8 a were observed relative to blood serum with in vitro deep-tissue imaging, thereby confirming its use as a promising PA contrast agent.

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.…”

Non‐invasive sentinel lymph node mapping and needle guidance using clinical handheld photoacoustic imaging system in small animal

“…PAI contrast is dependent on optical absorption by molecules, which can be endogenous (blood, melanin or even water) or exogenous (organic dyes, nanoparticles, quantum dots, etc.) .…”

Unveiling NIR Aza‐Boron‐Dipyrromethene (BODIPY) Dyes as Raman Probes: Surface‐Enhanced Raman Scattering (SERS)‐Guided Selective Detection and Imaging of Human Cancer Cells

“…[36][37][38][39][40][41] The chalcones undergo nitromethanea ddition to give the nitro adduct, which, upon reaction with ammonium acetate to form the aza-dipyrromethene followed by complexation with BF 3 ·OEt 2 ,y ield the target aza-BODIPY dyes (Schemes S1-S2,see the Supporting Information). [36][37][38][39][40][41] The chalcones undergo nitromethanea ddition to give the nitro adduct, which, upon reaction with ammonium acetate to form the aza-dipyrromethene followed by complexation with BF 3 ·OEt 2 ,y ield the target aza-BODIPY dyes (Schemes S1-S2,see the Supporting Information).…”

“…In addition to the frequentlyu sed commerciallya vailable Ramanr eporters such as crystal violet (CV), malachite green isothiocyanate (MGITC), 4-mercaptobenzoic acid (4-MBA), Rhodamine 6G, and diethylthiatricarbocyanine (DTTC), there has been increased interest in the development of new Ramans ignature molecules for diversed iagnostic and imaging applications. [36][37][38] The synthetic flexibility of these dyes make them attractive for diversea pplications such as sensitizers for photooxygenation, photodynamic therapy,a sw ell as probesf or anions, cations, and neutralmolecules. [26][27][28] Despite the diverse attempts to discover new Raman reporter molecules, mosto ft he reported approaches suffer from several disadvantages such as low resolution, short wavelength absorption and high fluorescenceb ackground, which may mask the Raman signals.…”