Pyrrolopyrrole aza-BODIPY Research Articles

Simultaneous sensing cyanide and fluoride by Lewis acidic atom regulated–chromophore reaction and applications in real samples

The development of visually fluorescent probes for CN− and F− in one system is challenging. In this paper, a trimethylsilicon-modified pyrrolopyrrole aza-BODIPY (PPAB) conjugate (PPAB-TMSA) was synthesized. By use of Lewis acidic atom regulated–chromophore reaction strategy, PPAB-TMSA was utilized for CN− and F− recognition with high selectivity and low limit of detection (1.3 and 12 nM for CN− and F−, respectively) for the first time. The sensing mechanism revealed that PPAB core was broken by CN− and F− ions through chromophore reaction and trimethylsilicon moiety as an additional F− recognition site could facilely regulate reactivity. As a result, 7.8-fold higher reaction rate of PPAB-TMSA towards CN− than that towards F− and large spectral shift (Δλab = 277 nm, Δλem = 172 nm) led to a distinguishable colometric and fluorescent signals. The practicability was demonstrated by visual detecting F− in toothpaste and CN− in food samples with PPAB-TMSA-loaded test paper. The quantitative detecting endogenous CN− in tapioca flour and bitter almond was successfully demonstrated. This work provides a convenient and visual assay for simultaneous detection CN− and F−, which displays potential applications in real samples.

A colorimetric and ratiometric fluorescent probe for recognizing fluoride ion based on new chromophore reaction

Fluoride ion plays crucial roles in many biological, chemical, medical and environmental processes. Constructing a highly sensitive florescent probe for naked-eye detection F− is of particular importance but remains challenging. In this work, we developed a colorimetric and ratiometric fluorescent probe of pyrrolopyrrole aza-BODIPY (PPAB)-based polymer (P1) for recognizing F−. In presence of F−, P1 showed obvious color change from green to yellow with absorption maximum blueshift from 670 nm to 340 nm. The weak emission of 697 nm changed to strong orange fluorescence with appearance of new broad emission with maximum bands at 520 and 642 nm. P1 was capable of sensitively and selectively detecting F− with a low detection limit of 0.07 μM. The sensing mechanism revealed that B–N bond cleavage and following hydrolysis of P1 induced by F− was responsible for the distinct colorimetric and ratiometric fluorescent signals. The results indicated that PPAB core was an efficient recognition unit for F− detection for the first time. Finally, P1-loaded silicone or test paper could detect F− by naked-eye signals. The probe can be successfully applied in real water samples to detect F− concentration.

Rational design and investigation of nonlinear optical response properties of pyrrolopyrrole aza-BODIPY-based novel push-pull chromophores.

Intramolecular charge transfer (ICT)-based chromophores are highly sought after for designing near-infrared (NIR) absorbing and emitting dyes as well as for designing materials for nonlinear optical (NLO) applications. The properties of these 'push-pull' molecules can easily be modified by varying the electronic donor (D) and acceptor (A) groups as well as the π-conjugation linker. This study presents a methodical approach and employs quantum chemical analysis to explore the relationship between the structural features, electro-optical properties, and the NLO characteristics of molecules with D-π-A framework. The one- and two-photon absorption (2PA), linear polarizability (α), and first hyperpolarizability (β) of some novel chromophores, consisting of a dimeric aza-Boron Dipyrromethene (aza-BODIPY) analogue, called, pyrrolopyrrole aza-BODIPY (PPAB), serving as the acceptor, have been investigated. The electronic donors used in this study are triphenylamine (TPA) and diphenylamine (DPA), and they are conjugated to the acceptor via thienyl or phenylene π-linkers. Additionally, the Hyper-Rayleigh Scattering (βHRS), which enables direct estimation of the second-order NLO properties, is calculated for the studied chromophores with 1064 nm excitation in acetonitrile. The β value shows a significant increase with increasing solvent polarity, indicating that the ICT plays a crucial role in shaping the NLO response of the studied molecules. The enhancement of the 2PA cross-section of the investigated molecules can also be achieved by modulating the combinations of donors and linkers. The results of our study indicate that the novel D-π-A molecules designed in this work demonstrate considerably higher hyperpolarizability values than the standard p-nitroaniline, making them promising candidates for future NLO applications.

A novel chromophore reaction-based pyrrolopyrrole aza-BODIPY fluorescent probe for H2S detection and its application in food spoilage.

In this work, we developed an aggregation-induced emission enhancement (AIEE) active and NIR emissive pyrrolopyrrole aza-BODIPY (PPAB) polymer (P1) for H2S detection for the first time. P1 showed obvious colorimetric change from green to yellow-green and ratiometric fluorescence "turn on" phenomenon with 167nm blue-shift (from dark red to bright green). The sensing mechanism revealed a novel chromophore reaction between imine in PPAB core and H2S was involved, leading to less conjugated product. It exhibited distinct advantages of good selectivity, high sensitivity, and low detection limit of 0.66μM. The potential applicability of P1 for H2S detection in the real samples (tap water, lake water and milk) was demonstrated. In addition, the solid sensor prepared by loading P1 on the PMMA film was successfully realized the visual detection of gaseous H2S gas produced from egg spoilage. Therefore, this work provides a promising approach based on novel sensing mechanism for monitoring H2S in complicated biological systems and practical food samples.

Tetracyanobuta-1,3-diene (TCBD)-appended pyrrolopyrrole aza-BODIPYs as a panchromatic chromophore based on the push-pull strategy

Pyrrolopyrrole aza-BODIPY (PPAB), a dimeric BODIPY analogue containing a pyrrolopyrrole structure at the center, exhibits intense far-red and near-infrared (NIR) absorption and emission. Herein, tetracyanobuta-1,3-diene-appended PPABs (TCBD-PPABs) were synthesized by post-modification based on a [2+2] cycloaddition-retroelectrocyclization (CA-RE) reaction with tetracyanoethylene. Owing to the redshift of the PPAB absorption in the NIR region and the emergence of the intramolecular charge-transfer band in the visible region, TCBD-PPABs exhibit panchromatic absorption in the visible/NIR regions.

Post-Modification of Pyrrolopyrrole Aza-BODIPY toward High Near-Infrared Fluorescence Brightness

Pyrrolopyrrole aza-BODIPYs (PPABs), dimeric aza-BODIPY analogues, exhibit intense absorption and fluorescence in the visible and near-infrared (NIR) regions. Here, we developed a facile postmodification by palladium-catalyzed coupling reactions to synthesize a series of donor-acceptor-donor (D-A-D) PPABs. Despite the possible fluorescence quenching dictated by the energy-gap low, D-A-D PPABs exhibit high-fluorescence brightness in the NIR region, implying their potential use as a bright NIR emitter.

Panchromatic small-molecule organic solar cells based on a pyrrolopyrrole aza-BODIPY with a small energy loss

A small photon energy loss (Eloss) is one of the requisites for achieving near-infrared (NIR) small-molecule organic solar cells (SM-OSCs). Herein, we present two novel pyrrolopyrrole aza-BODIPY (PPAB)-based panchromatic chromophores, TT-2PPAB and DFBT-2PPAB, with an acceptor-donor-acceptor configuration for photovoltaic studies. Among them, in combination with [6,6]-phenyl-C71 butyric acid methyl ester (PC71BM) acceptor, TT-2PPAB exhibits a moderate power conversion efficiency (PCE) of 3.11% due to an Eloss of 0.48 eV, which is smaller than the empirical limit of 0.6 eV. Based on the electrochemistry and theoretical calculations, we revealed that the efficient photovoltaic performance of the TT-2PPAB-based device can be ascribed to the sufficiently deep LUMO level of TT-2PPAB for charge transfer to PC71BM.

Pyrrolopyrrole-Based Aza-BODIPY Small Molecules for Organic Field-Effect Transistors.

Diketopyrrolopyrrole (DPP), due to its good planarity, π-conjugate structure, thermal stability, and structural modifiability, has received much attention from the scientific community as an excellent semiconductor material for its applications in the field of optoelectronics, such as organic solar cells, organic photovoltaics, and organic field effect transistors. In this study, a new small molecule, pyrrolopyrrole aza-BODIPY (PPAB), based on the thiophene-substituted DPP structure was developed using the Schiff-base formation reaction of DPP and heteroaromatic amines. Absorption spectroscopy, electrochemistry, X-ray diffraction, molecular theoretical simulation calculation were performed, and organic field-effect transistor properties based on PPAB were investigated. It was found that PPAB exhibits a broad absorption range in the visible and near-infrared regions, which is attributed to its long-range conjugate structure. In addition, it is worth noting that PPAB has multiple F atoms resulting in the low LUMO level, which is conducive to the injection and transportation of charge carriers between the semiconductor layer and the electrode. Meanwhile, its hole carrier mobility is up to 1.3 × 10−3 cm2 V−1 s−1 due to its large conjugate structure, good intramolecular charge transfer effect, and high degree of coplanarity. In this study, a new chromophore with electron-deficient ability for designing high-performance semiconductors was successfully synthesized.

An Electron-Accepting aza-BODIPY-Based Donor-Acceptor-Donor Architecture for Bright NIR Emission.

A bright near-infrared (NIR) fluorescent molecule was developed based on the donor-acceptor-donor (D-A-D) approach using an aza-BODIPY analog called pyrrolopyrrole aza-BODIPY (PPAB) as an electron-accepting chromophore. Directly introducing electron-donating triphenylamine (TPA) to develop a D-A-D structure caused redshifts of absorption and emission of PPAB into the NIR region with an enhanced fluorescence brightness of up to 5.2×104 m-1 cm-1 , whereas inserting a phenylene linker between the TPA donor and the PPAB acceptor induced solvatochromic behavior in emission. Transient absorption spectra and theoretical calculations revealed the presence of a highly emissive hybridized locally excited and charge-transfer state in the former case and the contribution of the dark charge-separated state to the excited state in the latter case. The bright D-A-D PPAB as a novel emitter resulted in a NIR electroluminescence with a high external quantum efficiency of 3.7 % and a low amplified spontaneous emission threshold of ca. 80 μJ cm-2 , indicating the high potential for NIR optoelectronic applications.

Pyrrolopyrrole aza-BODIPY dyes for ultrasensitive and highly selective biogenic diamine detection

Biogenic diamines (BAs) are important compounds in food chemistry and life science. Because of structural similarity of amines and low concentration of BAs in real samples, it is exceedingly challenging to design and develop highly efficient probes for visual detection of BAs. To address this gap, we report ultrasensitive and highly selective pyrrolopyrrole aza-BODIPY (PPAB) probes for BAs detection. The detection mechanism study revealed first kinetic-control reaction of a B–N bond cleavage by BAs, and following two fast step reactions (transimination and hydrolysis) to yield much smaller conjugated molecules. The first kinetic-control reaction results in high selectivity towards BAs. The following reactions result in direct large conjugation change, leading to high sensitivity for the detection of BAs. Thus, with over 225 nm hypsochromic shift in the absorption maximum and 12-fold fluorescence enhancement process, PPAB probes showed high sensitivity for BAs with limit of detection up to ppb level and response time on the second timescale. Moreover, visual detection of BAs vapors and monitoring fish spoilage were successfully conducted by the low-cost, high-contrasting, quick-responsive fluorescent trademark of PPAB molecules by naked-eyes.

Rational design of pyrrolopyrrole-aza-BODIPY-based acceptor-donor-acceptor triads for organic photovoltaics application.

Acceptor-donor-acceptor triads consisting of diketopyrrolopyrrole (DPP) or pyrrolopyrrole aza-BODIPY (PPAB) or both as acceptors and cyclopentadithiophene as a donor were rationally designed for near infrared (NIR) photovoltaics application. Among them, the PPAB-based triad exhibited the highest power conversion efficiency of 3.88% owing to the panchromatic absorption in the UV/vis/NIR regions.

Pyrrolopyrrole Aza-BODIPY Analogues as Near-Infrared Chromophores and Fluorophores: Red-Shift Effects of Substituents on Absorption and Emission Spectra.

Pyrrolopyrrole aza-BODIPY analogues (PPABs) are a new class of UV/vis and near-infrared chromophores. Varying the substituents results in red-shifts of both the absorption and emission spectra. Extension of the lengths of the oligothiophene substituents from thiophene to quaterthiophene caused red-shifts of the absorption and emission from 699 and 712 nm to 809 and 853 nm, respectively. The piperidylthiophene-substituted PPAB exhibited similar red-shifts of the absorption and emission to 810 and 831 nm, respectively, although only a single thienyl component is present, because of the strong electron-donating nature of the piperidine substituent.

Pyrrolopyrrole aza-BODIPY near-infrared photosensitizer for dual-mode imaging-guided photothermal cancer therapy.

A NIR photosensitizer pyrrolopyrrole aza-BODIPY (PPAB) was synthesized in a straightforward manner. Through the use of PPAB NPs as a photothermal agent, photoacoustic imaging (PAI) and NIR fluorescence imaging (NIR-FI) can be achieved in vivo. In addition, the photothermal ablation of tumor cells can be realized both in vitro and in vivo, even at a low concentration (0.5 mg kg-1).

A highly efficient, colorimetric and fluorescent probe for recognition of aliphatic primary amines based on a unique cascade chromophore reaction.

Pyrrolopyrrole aza-BODIPY based nanoaggregates were reported as a highly selective and sensitive probe for recognition of aliphatic primary amines with a novel cascade chromophore reaction. Due to its distinct reaction characteristics, this probe loaded test strip can conveniently detect n-hexylamine vapor and monitor the freshness of shrimp.

Blackening of aza-BODIPY analogues by simple dimerization: panchromatic absorption of a pyrrolopyrrole aza-BODIPY dimer

Dimerization of the so-called pyrrolopyrrole aza-BODIPY via a bithienyl linkage led to the creation of a novel black dye with dual emission and panchromatic absorption properties in the Vis/NIR region.

A facile synthesis of novel near-infrared pyrrolopyrrole aza-BODIPY luminogens with aggregation-enhanced emission characteristics.

Here we report the facile synthesis of two triphenylethylene-modified pyrrolopyrrole aza-BODIPY dyes with an aggregation-enhanced emission feature. NIR-emitting nanoparticles with remarkable photostability properties and applications in bioimaging were generated due to their good dispersity in water and biocompatibility.

Polymeric Self-Assemblies with Boron-Containing Near-Infrared Dye Dimers for Photoacoustic Imaging Probes.

Polymers containing pyrrolopyrrole aza-BODIPY (PPAB) and thiophene-bridged BODIPY dimers (TBD) having poly(ethylene glycol) (PEG) or PEGylated hyaluronic acid (HA) were prepared by facile conjugation approaches. Self-assemblies consisting of TBD-conjugated polymers more efficiently generated photoacoustic (PA) signals than PPAB-PEG conjugate upon irradiation with near-infrared pulsed laser light. Among dye-conjugated polymers examined, TBD-HA-PEG conjugates efficiently generated photoacoustic signals, 1.49-1.83 times stronger than that of commercially available indocyanine green (ICG). We found that the following two factors are essential to enhance PA signals from self-assemblies: (1) the formation of strongly interacting TBD aggregates and (2) enhancement of the elastic modulus of self-assemblies by conjugating TBDs with HA. TBD-conjugated HA derivatives circulated in blood vessels for a longer time (15.6 ± 4.9% injected dose (ID) in blood 24 h after injection) and more specifically accumulated in tumor tissues (17.8 ± 3.5% ID/g in tumor 24 h after injection) than ICG-conjugated HA derivatives, visualizing a tumor site more clearly. The cell uptake experiment of dye-HA conjugates indicates that ICG-conjugated polymers internalized into cells or merged with cell walls to emit strong fluorescence, while TBD-conjugated polymers were not internalized into cells. Because the disassembly of the TBD-conjugated HA derivatives is suppressed, aggregated TBDs emit weak fluorescence but efficiently generate strong PA signals in tumor tissues.

Rational molecular design towards Vis/NIR absorption and fluorescence by using pyrrolopyrrole aza-BODIPY and its highly conjugated structures for organic photovoltaics.

Pyrrolopyrrole aza-BODIPY (PPAB) developed in our recent study from diketopyrrolopyrrole by titanium tetrachloride-mediated Schiff-base formation reaction with heteroaromatic amines is a highly potential chromophore due to its intense absorption and fluorescence in the visible region and high fluorescence quantum yield, which is greater than 0.8. To control the absorption and fluorescence of PPAB, particularly in the near-infrared (NIR) region, further molecular design was performed using DFT calculations. This results in the postulation that the HOMO-LUMO gap of PPAB is perturbed by the heteroaromatic moieties and the aryl-substituents. Based on this molecular design, a series of new PPAB molecules was synthesized, in which the largest redshifts of the absorption and fluorescence maxima up to 803 and 850 nm, respectively, were achieved for a PPAB consisting of benzothiazole rings and terthienyl substituents. In contrast to the sharp absorption of PPAB, a PPAB dimer, which was prepared by a cross-coupling reaction of PPAB monomers, exhibited panchromatic absorption across the UV/Vis/NIR regions. With this series of PPAB chromophores in hand, a potential application of PPAB as an optoelectronic material was investigated. After identifying a suitable PPAB molecule for application in organic photovoltaic cells based on evaluation using time-resolved microwave conductivity measurements, a maximized power conversion efficiency of 1.27 % was achieved.

Pyrrolopyrrole aza-BODIPY analogues: a facile synthesis and intense fluorescence

Pyrrolopyrrole aza-BODIPY analogues were synthesized from diketopyrrolopyrrole and heteroaromatic amines in the presence of titanium tetrachloride. These novel compounds exhibit intense absorption in the visible region and strong emission with high fluorescence quantum yields greater than 0.8.