A water-soluble small molecular fluorescent sensor based on phosphazene platform for selective detection of nitroaromatic compounds

Nitro-aromatic compounds have a deleterious effect on the environment and they are extremely explosive. Therefore, societal concern about exposure to nitro-aromatic compounds encourages researchers to develop selective and sensitive detection platforms for nitro-aromatic compounds in recent years. In this paper, a new 100% water-soluble cyclotriphosphazene-based bridged naphthalene material (4) was prepared as a small molecule fluorescent sensor for ultra-selective detection of nitro-aromatic compounds. The chemical structure of 4 was extensively characterized by mass spectrometry and nuclear magnetic resonance spectroscopies (³¹P, ¹³C, ¹H). The photo-physical properties of the newly developed sensing system were investigated by steady-state fluorescence and UV-Vis absorption spectroscopies. The fluorescence sensor behaviors were extensively evaluated after treatment with the most commonly used metal cations, anions, competitive aromatic compounds, saccharides, and organic acids. The developed fluorescent sensing system (4) demonstrated ultra-selective fluorescence "turn-off" signal change toward nitro-aromatic compounds while other tested competitive species caused negligible changes. To evaluate selectivity, time-resolved, steady-state 3D-fluorescence and UV-Vis absorption spectroscopies were used in fully aqueous media. Moreover, theoretical calculations (density functional theory and time-dependent density functional theory) were applied and discussed to identify fluorescence sensing mechanisms toward nitroaromatic compounds for the presented sensing system.

Cyclotriphosphazene-Based "Butterfly" Fluorescence Probe for Lysosome Targeting

A cyclotriphosphazene-based "butterfly" fluorescence probe HCCP-MNI bearing two naphthalimide and morpholine units were developed for lysosome targeting. The synthesized HCCP-MNI exhibited stable fluorescence signals and was cytocompatible in the given concentration range. Co-localization experimental results showed that cells treated with the HCCP-MNI and a commercial dye (Lyso-Tracker Red DND-99) had overlapped fluorescence signals, demonstrating its targeting specificity to lysosomes. The developed HCCP-MNI may be used for cell tracking applications associated with the functionalities of lysosomes.

Synthesis, optical, and structural properties of bisphenol-bridged aromatic cyclic phosphazenes

Phenoxy- and naphthoxy-substituted bisphenol-bridged cyclic phosphazenes were synthesized in 2 steps and their thermal, photophysical, and electrochemical properties were investigated. The structures of the cyclic phosphazene compounds were determined by ESI-MS mass spectrometry and 1 H, 13 C, and 31 P NMR spectroscopies. The photophysical studies of phenoxy- and naphthoxy-substituted bridged cyclophosphazenes were investigated by means of absorption and fluorescence spectroscopies in different solvents. Thermal and electrochemical properties of the target compounds were also studied. Furthermore, the excimer emissions through intramolecular interactions in solution and in solid state were investigated by fluorescence spectroscopy and the theoretical calculations were performed in detail using DFT.

Synthesis of new cyclotriphosphazene derivatives bearing Schiff bases and their thermal and absorbance properties

In this study, a series of cyclotriphosphazene derivatives containing a Schiff base (3a-3d) were synthesized by the reactions of hexachlorocyclotriphosphazene (1) with bis-aryl Schiff bases ( 2a - 2d ) having different terminal groups (H, F, Cl, and Br). The products ( 3a - 3d ) were characterized by elemental and mass analyses, FT-IR, and ¹ H, ¹³ C, and ³¹ P NMR spectroscopies. Furthermore, the structure of compound 3a was also determined by X-ray crystallography. The thermal behaviors and the spectral properties of the new cyclotriphosphazene compounds ( 3a - 3d ) were investigated and the results were compared in the series.

Pyrene-BODIPY-substituted novel water-soluble cyclotriphosphazenes: synthesis, characterization, and photophysical properties

In the present work, pyrene-boron-dipyrromethene (BODIPY)-substituted novel water-soluble cyclotriphosphazene derivatives (6 and 7) were synthesized by click reactions between a cyclotriphosphazene derivative with a hydrophilic glycol side group (2) and BODIPYs (4 and 5). All of the new compounds (2, 6, and 7) were characterized by Fourier-transform infrared and nuclear magnetic resonance spectroscopy, as well as mass spectrometry and elemental analysis. The photophysical properties of the BODIPY-substituted cyclotriphosphazenes (6 and 7) were investigated by UV-Vis and fluorescence emission spectroscopy in water and water/solvent mixtures. It was found that the target compounds were soluble in water and could be potential candidates as water-soluble fluorescent dyes for the desired applications.

New perylenebisimide decorated cyclotriphosphazene heavy atom free conjugate as singlet oxygen generator

Perylenebisimide-cyclotriphosphazene based inorganic-organic system was synthesized by a multistep procedure. The substitution reaction of asymmetric perylenebisimide (PBI) derivative with the hexachloroyclotriphosphazene (trimer) resulted in the formation of fully PBI decorated cyclotriphosphazene (5). The identity of newly synthesized compound (5) was confirmed by using ³¹P, ¹H and ¹³C NMR spectroscopies and mass spectrometry. The photophysical (UV- Vis absorption, fluorescence emission, fluorescence lifetime and fluorescence quantum yield) and photochemical (the singlet oxygen generation, and photostability) properties of this conjugate were investigated as novel heavy atom free triplet photosensitizer. The singlet oxygen quantum yield of the PBI-cyclotriphosphazene (5) was calculated to be 0.86 which is good for a heavy atom free triplet photosensitizer. These results will add to the development of cyclotriphosphazene based heavy atom free singlet oxygen triplet photosensitizer systems for applications in organic oxygenation reactions.

Constitutional isomers of dendrimer-like pyrene substituted cyclotriphosphazenes: synthesis, theoretical calculations, and use as fluorescence receptors for the detection of explosive nitroaromatics

Two constitutionally isomeric bis-pyrenyl phenol dendrons (4 and 6) and their dendrimer-like cyclotriphosphazene derivatives (5 and 7) are designed, synthesized and fluorescence detection behaviors are evaluated for nitro aromatic compounds (NACs).

Excimer formation and evolution of excited state properties in discrete dimeric stacking of an anthracene derivative: a computational investigation

Herein, density functional theory (DFT) computations were performed to investigate the discrete dimer of a mono-substituted anthracene derivative (2-TA-AN), which exhibited highly efficient pure excimer fluorescence in its crystal form. As a more practical model, its geometry, potential energy curve and excited state property were systematically calculated to better understand the excimer formation process and photophysical properties. The compressed excimer geometry is responsible for the highly efficient excimer emission, arising from the enhanced rigidity that greatly suppresses its non-radiative vibrations. Potential energy curves along three directions reveal the non-uniqueness of excimer formation along the long axis of anthracene, which is in a good agreement with the experimental findings. Upon decreasing the displacement, the intermonomer charge-transfer (CT) component gradually increased towards an approximately equivalent hybridization with the locally-emissive (LE) state of the monomer during the formation of the excimer. The excimer emission wavelength versus intermonomer CT content shows a similar trend along the three directions, revealing a turning point related to the essential transition of the excited state properties from the LE of the monomer to the HLCT of the excimer. The present results will contribute to the better understanding of the structure-property relationships in excimer formation and photophysical properties.

A systematic series of fluorescence chemosensors with multiple binding sites for Hg(ii) based on pyrenyl-functionalized cyclotriphosphazenes and their application in live cell imaging

A systematic series of fluorescence chemosensors based on cyclotriphosphazene derivatives were designed, synthesized, and evaluated for their sensing behaviors toward metal ions.

Bis(1-pyrenylmethyl)-2-benzyl-2-methyl-malonate as a Cu2+ Ion-Selective Fluoroionophore

A new malonate possessing two pyrene moieties was synthesized as a fluoroionophore, and its structure and fluorescence spectroscopic properties were investigated. When excited at 344 nm in acetonitrile/chloroform (9:1, v/v), the synthesized bispyrenyl malonate has the fluorescence of intramolecular excimer (λ_em = 467 nm) emissions and not a pyrene monomer emission (λ_em = 394 nm). A large absolute fluorescence quantum yield was obtained in the solid state (Φ_PL = 0.65) rather than in solution (Φ_PL = 0.13). X-ray crystallography analysis clarified the molecular structure and alignment of the bispyrenyl malonate in the crystal phase, elucidating its fluorescence spectroscopic properties. Such analysis also suggests there are intramolecular C-H···π interactions and intermolecular π···π interactions between the pyrenyl rings. Interestingly, the synthesized bispyrenyl malonate exhibits excellent fluorescence sensing for the Cu²⁺ ion. Remarkable fluorescence intensity enhancement was only observed with the addition of the Cu²⁺ ion.

Octa-BODIPY derivative dendrimeric cyclotetraphosphazenes; photophysical properties and fluorescent chemosensor for Co2+ ions

We have designed and synthesized the first examples of fluorescent chemosensors based on octa-BODIPY decorated dendrimeric cyclotetraphosphazenes. The structures these synthesized compounds were verified by ¹H, ¹³C, ³¹P NMR spectroscopies and UV-vis electronic absorption spectra. The photophysical and metal sensing properties in THF solutions of dendrimeric cyclotetraphosphazenes (OBCP 1-3) were investigated by fluorescence spectroscopy. OBCP 1-3 showed strong absorption in the 500-640nm region with high molar extinction coefficients. Additionally, octa-BODIPY decorated dendrimeric cyclotetraphosphazenes are candidate for fluorescent chemosensor for Co²⁺ showing high selectivity with a low limit of detection.