Synthesis of π-expanded BODIPYs and their fluorescent properties in the visible–near–infrared region

New insight into the application of fluorescence platforms in tumor diagnosis: From chemical basis to clinical application

Early and rapid diagnosis of tumors is essential for clinical treatment or management. In contrast to conventional means, bioimaging has the potential to accurately locate and diagnose tumors at an early stage. Fluorescent probe has been developed as an ideal tool to visualize tumor sites and to detect biological molecules which provides a requirement for noninvasive, real-time, precise, and specific visualization of structures and complex biochemical processes in vivo. Rencently, the development of synthetic organic chemistry and new materials have facilitated the development of near-infrared small molecular sensing platforms and nanoimaging platforms. This provides a competitive tool for various fields of bioimaging such as biological structure and function imaging, disease diagnosis, in situ at the in vivo level, and real-time dynamic imaging. This review systematically focused on the recent progress of small molecular near-infrared fluorescent probes and nano-fluorescent probes as new biomedical imaging tools in the past 3-5 years, and it covers the application of tumor biomarker sensing, tumor microenvironment imaging, and tumor vascular imaging, intraoperative guidance and as an integrated platform for diagnosis, aiming to provide guidance for researchers to design and develop future biomedical diagnostic tools.

Nonsymmetric Benzo[a]fused and Thiophene/Thieno[3,2-b]thiophene[b]fused BODIPYs: Synthesis and Photophysical Properties

The fusion of sufficient-electron heterocycle rings into the[a]/[b]-position of the BODIPY core would result in a large redshift wavelength, thus achieving red or near infrared emission. In this paper, we described the synthesis of nonsymmetric benzo[a]fused and thiophene/thieno[3,2-b]thiophene[b]fused BODIPY derivatives 2-3 while containing a reactive site, and then, 4-7 were developed by nucleophilic substitution reactions of 3 with various nucleophilic agents in high yields. X-ray crystallographic analysis of 2-7 revealed that the core structure adopted a planar geometry and π-π interactions were observed in the packing structure. BODIPYs 4 and 6-7 displayed a hypochromic shift in the absorption and bathochromic shift in the emission with increasing solvent polarity because of the formation of resonance structures resulting from the change of the C-N distance, which was rationalized by density functional theory (DFT)/time-dependent-DFT calculations.

One-pot synthesis of N-confused porphyrin-dipyrrin conjugates and their optical properties

A conjugated N-confused porphyrin-dipyrrin system NCP-IN-X (X = H, Br, Cl, OMe, COOEt) has been reported via N-Confused tetraphenylporphyrin (NCTPP) as a π-enlarged pyrrole and substituted trimethylindole subunits in 75-82% yields by one pot. All the NCP-INs show red-shifted absorption and emission in the NIR range compared with NCTPP in a series nonpolar and polar solvents. Interesting, relative higher emission in DMF can be observed. The structures of dipyrrin-NCP conjugates are characterized by ¹H-NMR and high resolution mass spectrum (HR-MS). Four frontier molecular orbital and simulated stick absorption spectra are calculated by DFT and TD-DFT calculation which is in good agreement with the experiments.

Synthesis of near-infrared absorbing and fluorescing thiophene-fused BODIPY dyes with strong electron-donating groups and their application in dye-sensitised solar cells

Thiophene-fused BODIPY dyes with two diethylaminophenyl groups as strong donors demonstrated near-infrared (NIR) absorption (λ_max: 783–812 nm, ε: 119 500–145 900) and fluorescence (F_max: 862–916 nm, Φ_f: 0.02–0.12) in dichloromethane.

Recent advances in the synthesis of [a]-benzo-fused BODIPY fluorophores

This feature article summarizes the different strategies for the synthesis of [a]-benzo-fused BODIPYs that have been reported in the literature until 2018. These π-extended BODIPYs are promising fluorophores for bio-imaging and organic photovoltaic applications due to both their attractive photophysical properties in the near-infrared area and their higher (photo)chemical stability compared to conventional bis-styryl derivatives. The four main strategies described in this review can be used to access either directly the expected [a]-benzo-fused BODIPYs or through the di-/tetra-hydroisoindole.

Benzene-fused bis(acenaphthoBODIPY)s, stable near-infrared-selective dyes

Benzene-fused bis(acenaphthoBODIPY)s prepared by retro-Diels–Alder reaction of bicyclo[2.2.2]octadiene-fused precursors showed strong absorption bands in the near-infrared region and very weak absorptions in the visible region.

Benzene-fused bis(acenaphthoBODIPY)s prepared by retro-Diels–Alder reaction of bicyclo[2.2.2]octadiene-fused precursors showed strong absorption bands in the near-infrared region and very weak absorptions in the visible region.

Carbazole-based BODIPYs with ethynyl substituents at the boron center: solid-state excimer fluorescence in the VIS/NIR region

Carbazole-based BODIPYs 1–6 with several different substituents at the boron atom site were synthesized.

Optical limiting properties of 3,5-diphenyldibenzo-azaBODIPY at 532 nm

The optical limiting properties of 3,5-diphenyldibenzo-azaBODIPY at 532 nm in solution and in polymer thin films are explored.

NIR-fluorescent coumarin-fused BODIPY dyes with large Stokes shifts

A series of novel non-symmetrical coumarin-fused BODIPY dyes were synthesised. Their absorption and emission properties are strongly influenced by substitution in the coumarin moiety. Diethylamino-substituted dyes showed near-IR emission with large Stokes shifts (up to 144 nm) and good fluorescence quantum yields.

Rational design of fluorophores for in vivo applications

Several classes of small organic molecules exhibit properties that make them suitable for fluorescence in vivo imaging. The most promising candidates are cyanines, squaraines, boron dipyrromethenes, porphyrin derivatives, hydroporphyrins, and phthalocyanines. The recent designing and synthetic efforts have been dedicated to improving their optical properties (shift the absorption and emission maxima toward longer wavelengths and increase the brightness) as well as increasing their stability and water solubility. The most notable advances include development of encapsulated cyanine dyes with increased stability and water solubility, squaraine rotaxanes with increased stability, long-wavelength-absorbing boron dipyrromethenes, long-wavelength-absorbing porphyrin and hydroporphyrin derivatives, and water-soluble phthalocyanines. Recent advances in luminescence and bioluminescence have made self-illuminating fluorophores available for in vivo applications. Development of new types of hydroporphyrin energy-transfer dyads gives the promise for further advances in in vivo multicolor imaging.

Structural modification strategies for the rational design of red/NIR region BODIPYs

The structure–property relationships of red/NIR region BODIPY dyes is analyzed, so that trends in their photophysical properties can be readily compared.

Yellow NIR dye: π-fused bisbenzoBODIPYs with electron-withdrawing groups

Stable benzene-fused bisbenzoBODIPY with four cyano groups is ideal for a NIR-selective dye, which shows strong absorption in the NIR region and good transparency in the visible region.

Blue-to-orange color-tunable laser emission from tailored boron-dipyrromethene dyes

A series of meso-substituted boron-bipyrromethene (BODIPY) dyes are synthesized and their laser and photophysical properties systematically studied. Laser emission covering a wide visible spectral region (from blue to orange) is obtained by just changing the electron donor character of the heteroatom at position 8. The additional presence of methyl groups at positions 3 and 5 results in dyes with a photostability similar to that of the unsubstituted dye but with much improved efficiency. Correlation of the lasing properties of the different dyes to their photophysical properties provides inklings to define synthetic strategies of new BODIPY dyes with enhanced efficiency and modulated wavelength emission over the visible spectral region.