A Simple Central Seven‐Membered BOPYIN: Synthesis, Structural, Spectroscopic Properties, and Cellular Imaging Application

A novel central seven-membered BOPYOs: Synthesis, optical properities and optimization of BF2 removal

Many efforts have been made to enrich the variety of BF2 complexes because of their excellent optical properties. However, the investigation on seven-membered ring N, O-chelated BF2 complexes is rare due to their instability with the removal of BF2 unit. Herein, a novel seven-membered ring N, O-chelated BF2 complexes (BOPYOs) with dual-state emission has been synthesized via a facile method. The results of optical properties showed that the fluorescence quantum yield of BOPYO-2 with donor group on 1 and 2-position of 1-indanone unit is much higher than that of BOPYO-1, 3-5 in toluene. The emission spectra of BOPYO-6 or 7 have redshift phenomenon compared with BOPYO-1-5 with weak fluorescence intensity due to their highly distorted structure or intramolecular charge transfer (ICT) effect. BOPYOs show relatively moderate solid emission from orange to deep red color with 596 nm to 686 nm. On the contrary, fluorescence quantum yield of BOPYO-2 in solid is the lowest. The optical properties in solution and solid states are further supported by the single-crystal structure and DFT calculation. Furthermore, the investigation on optimization of BF2 removal shows that the corresponding precursors of BOPYOs could be obtained in protic solvents without adding other catalysts.

Recent Advances in N-Heterocyclic Small Molecules for Synthesis and Application in Direct Fluorescence Cell Imaging

Nitrogen-containing heterocycles are ubiquitous in natural products and drugs. Various organic small molecules with nitrogen-containing heterocycles, such as nitrogen-containing boron compounds, cyanine, pyridine derivatives, indole derivatives, quinoline derivatives, maleimide derivatives, etc., have unique biological features, which could be applied in various biological fields, including biological imaging. Fluorescence cell imaging is a significant and effective imaging modality in biological imaging. This review focuses on the synthesis and applications in direct fluorescence cell imaging of N-heterocyclic organic small molecules in the last five years, to provide useful information and enlightenment for researchers in this field.

N,O-Chelated Organoboron Complexes with Seven-Membered Rings

Organoboron complexes have gained considerable attention owing to their versatile chemical structures and excellent optical properties. Nevertheless, stable seven-membered organoboron complexes have rarely been reported because of their challenging synthesis. Herein, seven-membered N,O-boron-chelated dyes, whose photophysical properties have been thoroughly studied via spectroscopic tests and theoretical calculations, were synthesized from commercially available materials via a facile method. Single-crystal X-ray diffraction studies provided evidence of their seven-membered ring N,O-boron-chelated skeleton. These complexes produced singlet oxygen species under laser irradiation, endowing them with potential application as a photosensitizer to treat superficial tumors (B16 cells). Our study provided a new skeleton to construct versatile organoboron compounds and offered a strategy to design heavy-atom-free photosensitizers.

New insights into quantifying the solvatochromism of BODIPY based fluorescent probes

A simple semiempiric phenomenological approach is developed for quantifying the solvent effect on the absorption and emission properties of BODIPYs. It is based on a new rule describing the linear relationship between the difference (Stokes shift) and the sum (double Gibbs free energy of electron transfer) for absorption and emission wavenumbers derived from a combination of solvent functions of Liptay theory. This rule is correspondent to changes of dipole moments in the ground and excited states. High reliability and advantages of the developed approach in comparison with traditional methods of the analysis of the solvatochromism based on Dimroth-Reichard and Lippert-Mataga solvent scales are illustrated for selected BODIPYs exhibiting positive, negative, and near-zero solvatochromism.

BOPYIN-anil and BOPYIN-boranil complex: Synthesis, spectroscopic properties and ESIPT process

Two BOPYIN dyes (W-1 and W-2) were synthesized, and their structural and photophysical properties were investigated. The absorption bands of both dyes located at ca. 350 and 500 nm in diverse solvents. The absorption profiles are a linear combination of those of the BOPYIN core and the boranil or anil subunits. Their emission spectra were observed at ca. 565 and 540 nm with 14.2% and 77% quantum yield in CHCl3, respectively. The absorption, excitation and emission spectra for both dyes confirm that the boranil or anil moieties could be used as an input energy antenna for cascade energy transfer to the fluorescent BOPYIN residue at 540 nm. Subsequently, ESIPT process of W-1 is fast and more likely to occur in non-polar solvent investigated by DFT calculation.

Substituent effects on opticalproperties of pyrrolizine-fused BOPYIN

Three new pyrrolizine-fused BOPYINs (DAB-H, DAB-OMe, DAB-ester) have been reported in 26-35% yield. The relationship between structures and optical spectra was investigated, which all the compounds show large Stokes Shift (3146-3884 cm^-1) and high quantum yield (up to 99%) in solvents. Among these dyes, the decoration of electron donating/withdrawing groups on indole, pyrrole and pyrrolizine units has a significant impact on optical properties, especially emission spectra. The results suggested that electron withdrawing group on pyrrole and pyrrolizine units has hypsochromic shift on emission spectra (DAB-H, DAB-OMe, DAB-ester versus DAB-1,4,5). The optimized structure, electron distribution on frontier molecular orbital, energy gap and simulated stick spectra of DABs are discussed by Density Functional Theory (DFT) calculation. We claim the agreement between the experimental and theoretical absorption spectra.

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.

Tuning the excited-state intramolecular proton transfer (ESIPT) process of indole–pyrrole systems by π-conjugation and substitution effects: experimental and computational studies

A series of amino (NH)-type hydrogen-bonding (H-bonding) compounds, BNDAB-1–4, containing π-enlarged indole and β-ethoxycarbonyl-substituted pyrrole units were designed and synthesized.

Synthesis and Photophysical Behavior of a Highly Fluorescent Family of Unsymmetrical Organoboron Complexes Containing 5-(Pyridin-2-ylmethylene)imidazolidine-2,4-dione Moieties

A new and highly fluorescent family of unsymmetrical organoboron complexes containing 5-(pyridin-2-ylmethylene)imidazolidine-2,4-dione moieties has been synthesized in three steps. These compounds show strong absorptions covering a wide range of the UV-vis spectrum and are strongly emissive (ϕ_f of up to 0.92 in CH₃CN). Moreover, two fluorophores that include an alkyne or an azide group at the end of the alkyl chain and with potential utility in bioorthogonal chemistry have been developed. One of these, in which the glycol substituent provides an enhanced water solubility without compromising the fluorescence (ϕ_f = 0.85 in water), may be of particular importance.

A stable AIEgen cis-diarylethene-based ‘ESIPT’ benchmark

A stable AIEgen locked by the seven-membered ring hydrogen bond and steric hindrance which made ‘ESIPT’ take place. It features a highly fluorescence in aggregate and solid states and large Stokes shift in solution.