Red-Emitting, Acene-Doped Conjugated Polymer Nanoparticles that Respond Ratiometrically to Photogenerated 1O2

Toggling the Oxygen Affinity between Anthracenes and Naphthalenes

We present the design of an anthracenyl-naphthyl (ANT-NAPH) dyad and its application as a luminescent 4-stage photo switch. Both segments can individually react with singlet oxygen to switch off an optical response. In their initial form the larger ANT component reacts significantly faster and thus an ANTO2-NAPH stage is turned on, observed by optical response of the remaining NAPH. To reduce its reactivity, ANT is substituted with two pyridine rings. This concept is first investigated and quantified on ANT and NAPH as separated molecules. Upon protonation the reaction of ANT becomes significantly slower. For the three possible pyridyl isomers this effect increases along the order meta Collapse

Key Words

• Anthracene
• Endoperoxide
• Naphthalene
• Singlet Oxygen
• Switching

Collapse

MESH Headings Collapse

Grants

• Universität Potsdam

Collapse

Affiliation(s)

Werner Fudickar Department of Chemistry, University of Potsdam, Karl-Liebknecht-Str. 24-25, D-14476, Potsdam, Germany
Torsten Linker Department of Chemistry, University of Potsdam, Karl-Liebknecht-Str. 24-25, D-14476, Potsdam, Germany

Collapse

Self-Reporting Conjugated Polymer Nanoparticles for Superoxide Generation and Detection

Conjugated polymer nanoparticles (CPNs or Pdots) have become increasingly popular fluorophores for multimodal applications that combine imaging with phototherapeutic effects. Reports of CPNs in photodynamic therapy applications typically focus on their ability to generate singlet oxygen. Alternatively, CPN excited states can interact with oxygen to form superoxide radical anion and a CPN-based hole polaron, both of which can have deleterious effects on fluorescence properties. Here, we demonstrate that CPNs prepared from the common conjugated polymer poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(1,4-benzo-{2,1',3}-thiadiazole)] (PFBT, also known as F8BT) generate superoxide upon irradiation. We use the same CPNs to detect superoxide by doping them with a superoxide-responsive hydrocyanine dye developed by Murthy and co-workers. Superoxide induces off-to-on fluorescence switching by converting quenching hydrocyanine dyes to fluorescent cyanine dyes that act as fluorescence resonance energy transfer (FRET) acceptors for PFBT chromophores. Amplified FRET from the multichromophoric CPNs yields fluorescence signal intensities that are nearly 50 times greater than when the dye is excited directly or over 100 times greater when signal readout is from the CPN channel. The dye loading level governs the maximum amount of superoxide that induces a change in fluorescence properties and also influences the rate of superoxide generation by furnishing competitive excited state deactivation pathways. These results suggest that CPNs can be used to deliver superoxide in applications in which it is desirable and provide a caution for fluorescence-based CPN applications in which superoxide can damage fluorophores.

Effects of Graphene Oxide (GO) and Reduced Graphene Oxide (rGO) on Green-Emitting Conjugated Copolymer's Optical and Laser Properties Using Simulation and Experimental Studies

The properties of a conjugated copolymer (CP), poly[(9,9-Dioctyl-2,7-divinylenefluorenylene)-alt-co-(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene) (PDVF-co-MEH-PV), were investigated in the presence of graphene oxide (GO) and reduced graphene oxide (rGO) using absorption, fluorescence, laser, and time-resolved spectroscopy. CPs are usually dissolved in low-polar solvents. Although GO does not dissolve well, rGO and PDVF-co-MEH-PV dissolve in chloroform due to their oxygen acceptor sites. Hence, we studied rGO/PDVF-co-MEH-PV (CP/rGO), performing all experiments and simulations in chloroform. We performed simulations on PDVF-co-MEH-PV, approximate GO, and rGO using time-dependent density-functional theory calculations to comprehend the molecular dynamics and interactions at the molecular level. The simulation polymer used a tail-truncated oligomer model with up to three monomer units. The simulation and experimental results were in agreement. Further, the PDVF-co-MEH-PV exhibited fluorescence, laser quenching, rGO-mediated laser blinking, and spectral broadening effects when GO and rGO concentrations increased. The experimental and simulation results were compared to provide a plausible mechanism of interaction between PDVF-co-MEH-PV and rGO. We observed that for lower concentrations of rGO, the interaction did not considerably decrease the amplified spontaneous emissions of PDVF-co-MEH-PV. However, the fluorescence of PDVF-co-MEH-PV was considerably quenched at higher concentrations of rGO. These results could be helpful for future applications, such as in sensors, solar cells, and optoelectronic device design. To demonstrate the sensor capability of these composites, a paper-based sensor was designed to detect ethanol and nitrotoluene. An instrumentation setup was proposed that is cheap, reusable, and multifunctional.

Aggregation-induced emission nanoparticles with improved optical absorption for boosting fluorescence signal of tumors in vivo

Nanomaterial development has been extensively investigated for several decades to realize sensitive and accurate imaging of tumors in vivo. The manufacturing of nanoparticles with highly efficient tumor targeting and excellent optical properties is still an important research topic. The structure and composition ratio of materials that decisively contribute to the brightness and size of nanoparticles have a great influence on image sensitivity and tumor targeting efficiency. In this study, we developed aggregation-induced emission (AIE) nanoparticles with a widened light absorption window (nanoPMeOCN/BDP) to enable sensitive in vivo tumor imaging. The signal of nanoparticles is enhanced by integrating a high-density AIE polymer (PMeOCN) and light-absorbing fluorescent dye (BDP) in a nanoscopic space. BDP not only improves the light absorption of particles but also enhances the fluorescence signal of particles by effectively transferring absorbed energy to PMeOCN. The physically blended nanoPMeOCN/BDP show strong light absorption and improved sensitivity for the imaging of biological tissues because of their excellent optical performance compared to nanoPMeOCN of similar nanosizes (∼19 nm in size). In vivo imaging results further confirm that nanoPMeOCN/BDP can provide amplified signals with the successful accumulation of tumor tissue through the enhanced permeability and retention effect. We expect that the design strategy of nanoparticles with improved light absorption will provide a simple and general method for improving the accuracy of disease diagnosis.

Self-Sensitized and Reversible O2 Reactivity with Bisphenalenyls for Simple, Tunable, and Multicycle Colorimetric Oxygen-Sensing Films

Monitoring the levels of molecular oxygen (O₂) is critical for numerous applications, but there is still a long-standing challenge to develop robust and cost-effective colorimetric sensors that enable detection by changes in color. Current technologies employ chromophores that require additional additives, which inherently increase the cost and complexity. Here, we report that bisphenalenyls (PQPLs) function as the single active component for colorimetric O₂ sensing through their quantitative conversion into aromatic endoperoxides (EPOs). PQPLs display self-sensitizing reactivity: they are capable of generating singlet oxygen and binding it without the need for external photosensitizers. The rates of PQPL photooxygenation depend on the electron-donating ability of substituents, which highlights a simple strategy for tuning O₂ sensitivity. EPOs are stable under ambient conditions but can be thermally stimulated to convert back to PQPLs and concomitantly release O₂. Polymer-supported (PTMSP) films of PQPLs (2 wt %) reproduce these reactivity trends with a rapid red-to-colorless transition that is visible to the naked eye within 1 h of exposure and show a very low limit of detection (<5 ppm O₂). Films are chemically and thermally robust and maintain up to >99% of their original colorimetric response when reused and subjected to multiple cycles of photooxygenation and O₂ release. The simplicity and solution processability of these materials highlight their potential as "intelligent" inks for printable colorimetric sensors.

A biocompatible hydrogel as a template for oxidative decomposition reactions: a chemodosimetric analysis and in vitro imaging of hypochlorite

The self-assembly properties of new biocompatible, thermoreversible fluorescent hydrogels, composed of amino acid residues have been reported. A unique gel-to-sol transition is triggered by chemodosimetric interaction in the presence of hypochlorite.