Search Results (35)

We have designed novel push–pull systems based on CF₃-substituted pyridines and pyrimidines. The photophysical properties of these new fluorophores have been examined using both absorption and emission spectral analyses in acetonitrile solutions and solid states. All fluorophores proved to exhibit moderate absolute quantum yields of up to 0.33 in solutions and up to 0.12 in solid states, depending on their specific structures. Most fluorophores have demonstrated significant aggregation-induced emission behavior, making them suitable as robust and low-toxicity bioimaging agents for bioimaging studies. Comparison with known dyes and studies on various cell cultures demonstrated the selectivity of the obtained push–pull systems for visualizing lipid droplets. Full article

β-galactosidase (β-Gal) has emerged as a pivotal biomarker for the comprehensive investigation of diseases associated with cellular senescence. The development of a fluorescent sensor is of considerable importance for precisely detecting the activity and spatial distribution of β-Gal. In this study, we developed two excited-state-altering responsive fluorescent sensors (TF1 and TF2) for ratiometric detection of β-Gal. Two TCF dyes, composed of tricyanofuran (TCF) and naphthol units, feature electron “pull–push” systems and are quenched fluorescence by β-Gal. Upon β-Gal hydrolysis, a significant ratiometric shift in absorption from ca. 475 nm to 630 nm is observed, accompanied by the emergence of a fluorescence signal at ca. 660 nm. The enzyme-responsive optical red-shifts are attributed to the excited-state transition from intramolecular charge transfer (ICT) state to local excited (LE) state, which was confirmed by density functional theory (DFT) calculations. Both fluorescent sensors display exceptional sensitivity and selectivity for the response of β-Gal in PBS solution and are capable of tracking β-Gal within senescent A549 cells. This study introduces a framework for developing multimodal optical probes by systematically modulating excited-state properties, demonstrating their utility in senescence studies, diagnostic assay design, and therapeutic assessment. Full article

The intramolecular charge transfer behavior of push–pull dyes is the origin of their sensitivity to environment. Such compounds are of interest as probes for bioimaging and as biosensors to monitor cellular dynamics and molecular interactions. Those that are solvatochromic are of particular interest in studies of lipid dynamics and heterogeneity. The development of new solvatochromic probes has been driven largely by the need to tune desirable properties such as solubility, emission wavelength, or the targeting of a particular cellular structure. DFT calculations are often used to characterize these dyes. However, if a correlation between computed (dipole moment) and experimentally measured solvatochromic behavior can be established, they can also be used as a design tool that is accessible to students. Here, we examine this correlation and include case studies of the effects of probe modifications and conformation on dipole moments within families of solvatochromic probes. Indeed, the ground state dipole moment, an easily computed parameter, is correlated with experimental solvatochromic behavior and can be used in the design of new environment-sensitive probes before committing resources to synthesis. Full article

Thiophene ring-enhancing electron delocalization imparts unique properties to azoic chromophore tools. The novel TA-OH dye contains a push–pull π-electron system, including a thiophene-azo scaffold with a hydroxyl group at the ortho position to the azo bridge. The hydroxyl group is expected to lock the azo bridge in its trans conformation, concurring with the photostability and fastness of the dye. The single crystal analysis identified the molecule’s primary conjugation plane, and the theoretical analysis provided electronic pattern insights. The absorption behavior and the trans-to-cis conversion were examined from both experimental and theoretical perspectives. The effect of solvent polarity and the role of pH on the photophysical properties were explored. The solvent polarity strongly affects the absorbance spectrum of TA-OH, therefore potentially making NLO active. Additionally, TA-OH exhibited pH responsiveness akin to classic dichromatic pH indicators, with a noticeable color shift from red to blue observed as pH transitioned from neutral to alkaline. Absorbance titration experiments, along with experimental/theoretical determination of pKa, defined the pH sensing ability. Full article

In this work, we use UV-Vis and Raman spectroscopy to correlate the intensity of selected transitions to the onset of aggregation phenomena. Through TDDFT calculations, we rationalize the formation of H-aggregates and their influence on the observed changes in the UV-Vis spectra. A correlation between Raman intensity and the molar absorption coefficient is experimentally observed and theoretically rationalized. We develop this method by considering Disperse Orange 3 (DO3), a well-known push–pull azobenzene dye with strong optical absorption in the blue–green region of the visible spectrum, and the known tendency to form H-aggregates. Full article

Following the seminal discovery of Richard Feynman, several micromachines have been made that are capable of several applications, such as solar energy harvesting, remediation of environmental pollution, etc. Here we have synthesized a nanohybrid combining TiO₂ nanoparticle and light harvesting robust organic molecule RK1 (2-cyano-3-(4-(7-(5-(4-(diphenylamino)phenyl)-4-octylthiophen-2-yl)benzo[c][1,2,5] thiadiazol-4-yl)phenyl) acrylic acid) as a model micromachine having solar light harvesting ability potential for application in photocatalysis, preparation of solar active devices, etc. Detailed structural characterization, including High Resolution Transmission Electronic Microscopy (HRTEM) and Fourier-transform infrared spectroscopy (FTIR), has been performed on the nanohybrid. We have studied the excited-state ultrafast dynamics of the efficient push-pull dye RK1 in solution, on mesoporous semiconductor nanoparticles, and in insulator nanoparticles by streak camera (resolution of the order of 500 fs). The dynamics of such photosensitizers in polar solvents have been reported, and it has been observed that completely different dynamics occur when they are attached to the surface of the semiconductor/insulator nanosurface. A femtosecond-resolved fast electron transfer has been reported when photosensitizer RK1 has been attached to the surface of the semiconductor nanoparticle, which in turn plays a crucial role in the development of an efficient light harvesting material. The generation of reactive oxygen species as a result of femtosecond-resolved photoinduced electron injection in the aqueous medium is also investigated in order to explore the possibility of redox-active micromachines, which are found to be crucial for efficient and enhanced photocatalysis. Full article

Fluorescence imaging is constantly searching for new far-red emitting probes whose turn-on response is selective upon the interaction with specific biological targets. Cationic push-pull dyes could indeed respond to these requirements due to their intramolecular charge transfer (ICT) character, by which their optical properties can be tuned, and their ability to interact strongly with nucleic acids. Starting from the intriguing results recently achieved with some push-pull dimethylamino-phenyl dyes, two isomers obtained by switching the cationic electron acceptor head (either a methylpyridinium or a methylquinolinium) from the ortho to the para position have been scrutinized for their ICT dynamics, their affinity towards DNA and RNA, and in vitro behavior. By exploiting the marked fluorescence enhancement observed upon complexation with polynucleotides, fluorimetric titrations were employed to evaluate the dyes’ ability as efficient DNA/RNA binders. The studied compounds exhibited in vitro RNA-selectivity by localizing in the RNA-rich nucleoli and within the mitochondria, as demonstrated by fluorescence microscopy. The para-quinolinium derivative showed some modest antiproliferative effect on two tumor cell lines as well as improved properties as an RNA-selective far-red probe in terms of both turn-on response (100-fold fluorescence enhancement) and localized staining ability, attracting interest as a potential theranostic agent. Full article

Push–pull dyes exhibit intramolecular charge transfer behavior, which due to changes in the dipole moment upon excitation, is the origin of their sensitivity to the environment. Such compounds are of interest as probes for bioimaging and as biosensors to monitor cellular dynamics and molecular interactions. Desirable biological probes absorb in the visible region, have high extinction coefficients, high quantum yield and excellent photostability. Fluorophores with scaffolding that can be used to tune and optimize solvatochromic behavior are of particular interest. Here, we investigate the environmental sensitivity of a small library of highly fluorescent 2,7-disubstituted sila- and germafluorenes. Density functional theory (DFT) calculations show that charge transfer occurs from the alkyne core out to the 2,7-substitutents and 3,6-methoxy substituents, the hallmark of push–pull behavior. They exhibit HOMO–LUMO energy gaps of about 3 eV with desirable dipole moments ranging from 2 to 9 D. These compounds exhibit desirable Stokes shifts in various solvents (25 to 102 nm). Interestingly, silafluorene with a benzaldehyde substituent exhibits competitive solvatochromic behavior. With the ability to tune push–pull properties via the 2,7-substituent, these disubstituted sila- and germafluorenes have excellent potential as biological probes. Full article

Fifteen push-pull dyes comprising the tetracyclic polyaromatic pyrene have been designed and synthesized. The optical properties of the fifteen dyes have been examined in twenty-two solvents of different polarities. Surprisingly, contrarily to what is classically observed for push-pull dyes of D-π-A structures, a negative solvatochromism could be found for numerous dyes. The photoluminescence and thermal properties of the dyes were also examined. Theoretical calculations were carried out to support the experimental results. Full article

A new Near InfraRed (NIR) fluorescent chemosensor for metal ions and anions is herein presented. The fluorophore is based on a styrylflavylium dye, a synthetic analogue of the natural anthocyanin family, with a di-(2-picolyl)amine (DPA) moiety as the metal chelating unit. The substitution pattern of the styrylflavylium core (with tertiary amines on positions 7 and 4′) shifts the optical properties of the dye towards the NIR region of the electronic spectra, due to a strong push-pull character over the π-conjugated system. The NIR chemosensor is highly sensitive to the presence of Zn²⁺, which induces a strong CHelation Enhanced Fluorescence (CHEF) effect upon binding to the DPA unit (2.7 fold increase). The strongest competing ion is Cu²⁺, with a complete fluorescence quenching, while other metals induce lower responses on the optical properties of the chemosensor. Subsequent anion screening of the Zn²⁺-chemosensor coordination compound has demonstrated a distinct selectivity towards adenosine 5′-triphosphate (ATP) and adenosine 5′-diphosphate (ADP), with high association constants (K ~ 10⁶ M⁻¹) and a strong CHEF effect (2.4 and 2.9 fold fluorescence increase for ATP and ADP, respectively). Intracellular studies with the Zn²⁺-complexed sensor showed strong luminescence in the cellular membrane of Gram^– bacteria (E. coli) and mitochondrial membrane of mammalian cells (A659), which highlights its possible application for intracellular labelling. Full article

Research in photochemistry is always looking for novel compounds that can serve a role in applications ranging from medicine to environmental science. Push–pull compounds with protonable groups represent an interesting class of molecules in this sense, as they can prove to be sensitive to changes in both the acidity and polarity of the medium, becoming valuable as sensors and probes. Hence, in this work, a new dinitrophenyl-hydrazinylidene derivative with multiple protonable centers has been specifically designed and synthesized. The molecule showed an important acidochromism in the visible, with three differently-protonated species under acidic, neutral, and basic conditions, each characterized by a peculiar absorption spectrum. The photophysical characterization of this compound revealed an ultrafast excited-state deactivation, as described by femtosecond transient absorption experiments, and the hints of charge-transfer dynamics, as supported by the observed solvatochromism and quantum-mechanical calculations. These properties led to almost undetectable fluorescence that, together with negligible intersystem crossing and the absence of reactive pathways, points to the preference for a total non-radiative deactivation mechanism, i.e., internal conversion. This intriguing behavior stimulates interest in light of possible applications of the investigated acidochromic dye as a probe in photoacoustic imaging, which offers an alternative to classical fluorescence imaging. Full article

The intensive research for hybridization probes based on organic molecules with fluorogenic properties is currently attracting particular attention due to their potential to efficiently recognize different DNA conformations and the local environment. However, most established organic chromophores do not meet the requirements of this task, as they do not exhibit good brightness in aqueous buffer media, develop aggregation and/or are not easily conjugated to oligodeoxynucleotides (ODNs) while keeping their photophysics intact. Herein, an important modification strategy was employed for a well-known fluorophore, 2-(4-(diethylamino)phenyl)-3-hydroxychromone (dEAF). Although this push–pull dye absorbs intensively in the visible range and shows emission with large Stokes shifts in all organic solvents, it is strongly quenched in water. This Achilles’ heel prompted us to implement a new strategy to obtain a series of dyes that retain all the photophysical features of dEAF in water, conjugate readily with oligonucleotides, and furthermore demonstrate sensitivity to hydration, thus paving the way for a high-performance fluorogenic DNA hybridization probe. Full article

An investigation on the photoelectrochemical and sensitizing properties of two different hybrid organic dyes, anchored as sensitizers on mesoporous TiO_2, in Grätzel solar cells, is presented. Firstly, we studied the absorption properties of the C106 sensitizer, a Ru polypyridine complex, and of the Y123, an organic push and pull dye. In this work, we characterized these two dyes, employing two different electrolytes, with similar experimental condition and device parameters. From the J–V curves and IPCE photo action spectra, we performed an inedited bifacial study based on the comparison of their photovoltaic performances, exploiting several backgrounds (black or white). Among the obtained results from this study, we found the best bifaciality factor of 93% for C106 and the best power conversion efficiency of 12.8% for Y123. These results represent, concerning these two dyes and to the best of our knowledge, some of the highest values in literature. Full article

1,4-Bis(p-tolylamino)-6,7-dichloroanthraquinone 1 when reacted with di(sodiothio)-maleonitrile 2 afforded heterocyclic thianone compound, 5,12-dioxo-5,12-dihydroanthro[2,3-b][1,4]dithiine-2,3-dicarbonitrile 3. Using lithium/pentanol and acetic acid, the dicarbonitrile product 3 was cyclotetramerized, yielding the matching tetra 5,12-dioxo-5,12-dihydroanthro[2,3-b][1,4]dithiine-porphyrazine dye compound (2H-Pz) 4a. The dicarbonitrile molecule was a ring-shaped metallic product utilizing metallic salt and quinoline, yielding the corresponding tetra 5,12-dioxo-5,12-dihydroanthro[2,3-b][1,4]dithiine-porphyrazinato-metal II dyes (M-Pz), M = Zn, Co, or Ni 4b–d. The produced compounds’ elemental analysis investigation, Infrared, and nuclear magnetic resonance spectrum information accord with the structures attributed to them. The cyclotetramerization and complexation reactions are ensured by the molecular weight and metal load of the produced products. The inclusion of electron-donating groups resulted in a lower optical band gap of the produced dye sensitizers, with “push–pull” promotion of about 1.55 eV. The prepared substituted porphyrazines reveal high absorption in the UV–VIS region, which could be of potential value as a building block for novel electronic and optical materials as well as a sensor for technology. This is considered for improving solar cell absorption. The absorption bands of the synthesized porphyrazine dyes extend beyond 800 nm, so these dyes could be useful in various optoelectronic applications. Full article

The trapping of coronene and zinc phthalocyanine (ZnPc) molecules at low concentration by a two-dimensional self-assembled nanoarchitecture of a push–pull dye is investigated using scanning tunneling microscopy (STM) at the liquid–solid interface. The push–pull molecules adopt an L-shaped conformation and self-assemble on a graphite surface into a hydrogen-bonded Kagomé network with porous hexagonal cavities. This porous host-structure is used to trap coronene and ZnPc guest molecules. STM images reveal that only 11% of the Kagomé network cavities are filled with coronene molecules. In addition, these guest molecules are not locked in the host-network and are desorbing from the surface. In contrast, STM results reveal that the occupancy of the Kagomé cavities by ZnPc evolves linearly with time until 95% are occupied and that the host structure cavities are all occupied after few hours. Full article