Dipyrrolonaphthyridinedione - (still) a mysterious cross-conjugated chromophore

Dipyrrolonaphthyridinediones (DPNDs) entered the chemical world in 2016. This cross-conjugated donor-acceptor skeleton can be prepared in two steps from commercially available reagents in overall yield ≈15-20% (5 mmol scale). DPNDs can be easily and regioselectively halogenated which opens an avenue to numerous derivatives as well as to π-expansion. Although certain synthetic limitations exist, the current derivatization possibilities provided impetus for numerous explorations that use DPNDs. Structural modifications enable bathochromic shift of the emission to deep-red region and reaching the optical brightness 30 000 M-1 cm-1. Intense absorption and strong emission of greenish-yellow light attracted the interest which eventually led to the discovery of their strong two-photon absorption, singlet fission in the crystalline phase and triplet sensitization. Dipyrrolonaphthyridinedione-based twistacenes broadened our knowledge on the influence of twisting angle on the fate of the molecule in the excited state. Collectively, these findings highlight the compatibility of DPNDs with various applications within organic optoelectronics.

Mitochondrial Targeting and Imaging with Small Organic Conjugated Fluorophores: A Review

The last decade has seen an increasingly large number of studies reporting on the development of novel small organic conjugated systems for mitochondrial imaging exploiting optical signal transduction pathways. Mitochondria are known to play a critical role in a number of key biological processes, including cellular metabolism. Importantly, irregularities on their working function are nowadays understood to be intimately linked to a range of clinical conditions, highlighting the importance of targeting mitochondria for therapeutic benefits. In this work we carry out an in-depth evaluation on the progress to date in the field to pave the way for the realization of superior alternatives to those currently existing. The manuscript is structured by commonly used chemical scaffolds and comprehensively covers key aspects factored in design strategies such as synthetic approaches as well as photophysical and biological characterization, to foster collaborative work among organic and physical chemists as well as cell biologists.

A sensitive zinc probe operating via enhancement of excited-state intramolecular charge transfer

Novel highly sensitive fluorescent probes for zinc cations based on the diketopyrrolopyrrole scaffold were designed and synthesized. Large bathochromic shifts (≈80 nm) of fluorescence are observed when the Zn²⁺-recognition unit (di-(2-picolyl)amine) is bridged with the fluorophore possessing an additional pyridine unit able to participate in the coordination process. This effect originates from the dipolar architecture and the increasing electron-withdrawing properties of the diketopyrrolopyrrole core upon addition of the cation. The new, greenish-yellow emitting probes, which operate via modulation of intramolecular charge transfer, are very sensitive to the presence of Zn²⁺. Introduction of a morpholine unit in the diketopyrrolopyrrole structure induces a selective six-fold increase of the emission intensity upon zinc coordination. Importantly, the presence of other divalent biologically relevant metal cations has negligible effects and typically even at a 100-fold higher concentration of Mg²⁺/Zn²⁺, the effect is comparable. Computational studies rationalize the strong bathochromic shift upon Zn²⁺-complexation. Decorating the probes with the triphenylphosphonium cation and morpholine unit enables selective localization in the mitochondria and the lysosome of cardiac H9C2 cells, respectively.

Mitochondrial Targeting of Probes and Therapeutics to the Powerhouse of the Cell

Mitochondria, colloquially known as "the powerhouse of the cell", play important roles in production, but also in processes critical for cellular fate such as cell death, differentiation, signaling, metabolic homeostasis, and innate immunity. Due to its many functions in the cell, the mitochondria have been linked to a variety of human illnesses such as diabetes, cancer, and neurodegenerative diseases. In order to further our understanding and pharmaceutical targeting of this critical organelle, effective strategies must be employed to breach the complex barriers and microenvironment of mitochondria. Here, we summarize advancements in mitochondria-targeted probes and therapeutics.

Two Novel Fluorescent Probes as Systematic Sensors for Multiple Metal Ions: Focus on Detection of Hg2

Many precedents prove that fluorescent probes are promising candidates for detection of metal ions in the environment and biological systems. Herein, two novel photoinduced electron transfer (PET)-based fluorescent probes, CH 3 -R6G and CN-R6G, were rationally synthesized by incorporating a triazolyl benzaldehyde moiety into the rhodamine 6G fluorophore. The optical properties of these probes were studied using an ultraviolet-visible (UV-vis) absorption spectrophotometer and a fluorescence spectrophotometer. Through the analysis of the test results, it is concluded that the selectivity and sensitivity of these two probes to Hg2+ are better than to other metal ions (Ag+, Al3+, Ba2+, Cd2+, Co3+, Cu2+, Cr3+, Fe3+, Ga2+, K+, Mg2+, Na+, Ni2+, Pb2+, and Zn2+). According to the standard curve diagram, the detection limits of CH 3 -R6G and CN-R6G were determined to be 1.34 × 10-8 and 1.56 × 10-8 M, respectively. Reaction of the probes with Hg2+ resulted in a color change of the solution from colorless to pink. The corresponding molecular geometric configuration, orbital electron distribution, and orbital energy of these two compounds were predicted by density functional theory (DFT). The two probes CH 3 -R6G and CN-R6G have been successfully used for imaging Hg2+ in live breast cancer cells, thereby indicating their great potential for the micro-detection of Hg2+ in vivo.

Dual-Functionalisation of Fluorophores for the Preparation of Targeted and Selective Probes

A key current challenge in biological research is the elucidation of the that roles chemicals and chemical reactions play in cellular function and dysfunction. Of the available cellular imaging techniques, fluorescence imaging offers a balance between sensitivity and resolution, enabling the cost-effective and rapid visualisation of model biological systems. Importantly, the use of responsive fluorescent probes in conjunction with ever-advancing microscopy and flow cytometry techniques enables the visualisation, with high spatiotemporal resolution, of both specific chemical species and chemical reactions in living cells. Ideal responsive fluorescent probes are those that contain a fluorophore tethered to both a sensing unit, to ensure selectivity of response, and a targeting group, to control the sub-cellular localisation of the probe. To date, probes that are both targeted and selective are relatively rare and most localised probes are discovered serendipitously rather than by design. A challenge in this field is therefore the identification of suitable fluorophore scaffolds that can be readily attached to both sensing and targeting groups. Here we review current strategies for dual-functionalisation of fluorophores, highlighting key examples of targeted, responsive probes.

An AIE and PET fluorescent probe for effective Zn(ii) detection and imaging in living cells

A sensitive fluorescent probe L for Zn²⁺ with aggregation-induced emission (AIE) properties has been synthesized.

A fluorescent sensor for intracellular Zn2+ based on cylindrical molecular brushes of poly(2-oxazoline) through ion-induced emission

Poly(2-oxazoline) molecular brushes bearing enaminitrile receptors in the side chain ends exhibit good biocompatibility, excellent fluorescent selectivity for Zn²⁺, and possibility in detecting intracellular Zn²⁺.

A novel fluorescent probe for the early detection of prostate cancer based on endogenous zinc sensing

BACKGROUND

The early detection of prostate cancer can significantly optimize the prognosis, prolong patient lifespan, and improve quality of life. It has been well documented that prostate cancer tissues have lower zinc content than normal prostate tissues due to an impairment of the zinc accumulation mechanism.

METHODS

A novel diketopyrrolopyrrole (DPP)-based fluorescent zinc ion probe named DPP-C2 was prepared. The fluorescent intensity of this novel molecule is in direct proportion to environmental zinc concentration. Malignant (DU145 and PC3 cells) and normal prostate epithelial RWPE-1 cells were tested. Prostate cancer tissues were also cultured and observed as tissue sections. The probe was also intravenously administered to tumor-bearing (DU145 and PC3 cells) nude mice and observed under a whole-body fluorescence live-imaging system.

RESULTS

The probe showed minimal cytotoxicity to malignant and normal prostate cells. The RWPE-1 cells showed not only stronger baseline fluorescence but also a significant increase in signal intensity after culturing in a zinc-supplemented medium. In human prostate sections, the pathologically confirmed cancer tissues exhibited weaker fluorescence signals than normal and benign hyperplastic tissues. With proper excitation, prostate tissues revealed more intense fluorescence signals than tumor tissues, whereas other surrounding tissues showed almost no fluorescence.

CONCLUSIONS

The novel zinc ion fluorescent probe DPP-C2 is low toxic and showed potential application for the early detection of prostate cancer based on endogenous zinc sensing.

Diketopyrrolopyrrole-based fluorescence probes for the imaging of lysosomal Zn2+ and identification of prostate cancer in human tissue

A series of diketopyrrolopyrrole-based fluorescent probes (DPP-C2, LysoDPP-C2, LysoDPP-C3, and LysoDPP-C4) have been developed for the detection of low pH and Zn2+ in an AND logic fashion. The chelation of Zn2+ or the protonation of a morpholine moiety within these probes results in a partial increase in the fluorescence intensity, an effect ascribed to suppression of one possible photo-induced electron transfer (PET) pathway. In contrast, a large increase in the observed fluorescence intensity is observed at low pH and in the presence of Zn2+; this is rationalized in terms of both possible PET pathways within the probes being blocked. Job plots, fluorescence titration curves, and isothermal titration calorimetry proved consistent with a 1 : 1 Zn2+ complexation stoichiometry. Each probe demonstrated an excellent selectivity towards Zn2+ and the resulting Zn2+ complexes demonstrated pH sensitivity over the 3.5-9 pH range. Fluorescence imaging experiments confirmed that LysoDPP-C4 was capable of imaging lysosomal Zn2+ in live cells. Little evidence of cytotoxicity was seen. LysoDPP-C4 was successfully applied to the bioimaging of nude mice, wherein it was shown capable of imaging the prostate. Histological studies using a human sample revealed that LysoDPP-C4 can discriminate cancerous prostate tissue from healthy prostate tissue.

Fluorinated dithienyl-diketopyrrolopyrrole: a new building block for organic optoelectronic materials

The synthesis of monofluorinated and difluorinated dithienyl-DPP was reported using a stepwise synthesis method starting from the preparation of pyrrolinone followed by condensation with methyl thiophene-2-carbimidate derivatives.

Amidinium–carboxylate salt bridge mediated proton-coupled electron transfer in a donor–acceptor supramolecular system

A supramolecular polymer that allows for intrapolymer proton-coupled photoinduced electron transfer was constructed by means of amidinium-carboxylate salt bridges.

A highly selective fluorescence turn-on chemosensor for Zn2+, and its application in live cell imaging, and as a colorimetric sensor for Co2+: experimental and TD-DFT calculations

A highly sensitive quinoline based “dual” chemosensor used for fluorometric detection of Zn²⁺, live-cell imaging, and colorimetric detection of Co²⁺.