Red-shifted Absorption Research Articles

A cycloruthenated 2-phenylimidazole: chromogenic sensor for nitrite in acidic buffer and fluoride in CH3CN

A cycloruthenated 2-phenylimidazole as a colorimetric sensor can detect fluoride in CH3CN by a great red-shift in absorption. However, it demonstrated sensitivity and selectivity to nitrite rather than fluoride in acidic buffer.

Fluorescent α-amino acids via Heck-Matsuda reactions of phenylalanine-derived arenediazonium salts.

The Heck-Matsuda coupling reaction of arenediazonium salts derived from L-phenylalanine with various alkenes has been developed. A two-step process involving the preparation of a tetrafluoroborate diazonium salt from a 4-aminophenylalanine derivative, followed by a palladium(0)-catalysed Heck-Matsuda coupling reaction allowed access to a range of unnatural α-amino acids with cinnamate, vinylsulfone and stilbene side-chains. Analysis of the photophysical properties of these unnatural α-amino acids demonstrated that the (E)-stilbene analogues exhibited fluorescent properties with red-shifted absorption and emission spectra and larger quantum yields than L-phenylalanine.

Distorted B/O-containing nanographenes with tunable optical properties.

We report the synthesis of two B/O-containing nanographenes, which feature the fusion of three or six planar B/O-heterocycles onto one hexa-peri-hexabenzocoronene π-framework. Incorporation of the B/O-heterocycles not only leads to distorted geometries, but also modulates the electronic structures and results in gradually red-shifted absorptions and fluorescence.

Fabrication of Eco-friendly UV-visible Driven Ni:CaCO3 Photocatalyst for Sustainable Environmental Remediation

Nano CaCO3, polymethyl methacrylate (PMMA) decorated Ni-doped CaCO3 nanoparticles (CPN) were synthesized from natural calcium magnesium carbonate (CaMg(CO3)2) via biomimetic synthetic route. The obtained products were thoroughly characterized through various physico-chemical techniques such as UV-DRS, PL, FTIR, XRD, TG-DTA, FE-SEM with EDX mapping, HR-TEM and SAED patterns. The XRD results revealed that the prepared products were in pure rhombohedral structure with the size range of 20-50 nm, respectively. Compared to other synthesized products, the sample CPN6 exhibited a blue-shifted band gap (2.7 eV) and red-shifted absorption and emission values. The morphological analysis of the samples shows the aggregated and rhombohedral with high porous like structure. The TG-DTA analysis shows the good thermal stability (up to 830 ºC). The photocatalytic activity exhibits a higher degradation efficiency 87% and 97% against methylene blue and rhodamine B dyes, respectively. The effect of different scavenger agents (ascorbic acid, AgNO3, EDTA2NA and isopropanol acid) was used to examine the efficiency of the photocatalytic activity. Based on the results, the prepared CPN6 nanoparticles show a great potential candidate for removal of organic dyes in the aqueous medium.

Furan Donor for NIR-II Molecular Fluorophores with Enhanced Bioimaging Performance.

The second near-infrared (NIR-II, 1,000 to 1,700 nm) molecular fluorophores containing donor-acceptor-donor conjugated backbone have attracted substantial attention due to their outstanding advantages, such as stable emission and facilely tuned photophysical properties. However, it is still challenging for them to simultaneously achieve high brightness and red-shifted absorption and emission. Herein, furan is adopted as the D unit to construct NIR-II fluorophores, demonstrating red shift of absorption, enhanced absorption coefficient, and fluorescent quantum yield when compared with the generally used thiophene counterparts. The high brightness and desirable pharmacokinetics of the optimized fluorophore, IR-FFCHP, endows improved performance for angiography and tumor-targeting imaging. Furthermore, dual-NIR-II imaging of tumor and sentinel lymph nodes (LNs) has been achieved with IR-FFCHP and PbS/CdS quantum dots, enabling the in vivo imaging navigated LN surgery in tumor-bearing mice. This work demonstrates the potential of furan for constructing bright NIR-II fluorophores for biological imaging.

Regulating steric hindrances of perylenediimide to construct NIR photothermal J-aggregates with a large red-shift.

Perylene diimide (PDI)-based photothermal agents (PTAs) possess excellent stability and high photothermal conversion efficiency. However, developing PDIs with strong near-infrared absorption under biological conditions remains a challenge. In this study, we introduce a novel approach to facilitate the formation of J-aggregate-based PTAs with significantly red-shifted absorption by modulating steric hindrances of PDIs. PDIA, featuring larger steric hindrances at the bay position and smaller steric hindrances at the imide position, self-assembles into J-aggregates which exhibit a remarkable red-shift of over 100 nm. After encapsulation by DPSE-PEG, PDIA nanoparticles (PDIA-NPs) demonstrated a uniform and stable size, while retaining their significant red-shift. In vitro experiments demonstrated the great potential of PDIA-NPs in photothermal therapies for tumors and thrombi under 808 nm laser irradiation. This research provides valuable insights into the design of stable J-aggregates based on PDIs suitable for biological applications, paving the way for the development of more effective PTAs.

Infrared spectrum of the 1-cyanoadamantane cation: evidence of hydrogen transfer and cage-opening upon ionization.

The radical cations of diamondoids are important intermediates in their functionalization reactions and are also candidates as carriers for astronomical absorption and emission features. Although neutral diamondoids have been studied extensively, information regarding their radical cations is largely lacking, particularly for functionalized diamondoid derivatives. Herein, we characterize the structure of the 1-cyanoadamantane radical cation (C10H15CN+, AdCN+) using infrared photodissociation (IRPD) spectroscopy of mass selected AdCN+N2 clusters in the XH stretch range (2400-3500 cm-1) and dispersion-corrected density functional theory calculations (B3LYP-D3BJ/cc-pVTZ). A group of three distinct CH stretch bands are observed in the 2800-3000 cm-1 range, in addition to a highly redshifted absorption at 2580 cm-1 attributed to the acidic CH proton predicted by calculations. An unexpected broad absorption peaking at 3320 cm-1 is also detected and assigned to an NH stretch mode based on its width and frequency. Calculations indicate that hydrogen atom transfer (HAT) from the adamantyl cage (C10H15, Ady) to the N atom of the CN group yields lower energy structures, with an open-cage isomer exhibiting such hydrogen transfer being the global minimum on the potential energy surface. The energy barriers involved in the formation of this open-cage isomer are also lower than those calculated for generation of the analogous open-cage 1-amantadine cation isomer which has previously been identified by IRPD. The combined consideration of IRPD spectra and calculations indicates a major population of the nascent canonical closed-cage isomer and a smaller population of the global minimum isomer featuring both cage-opening and hydrogen transfer.

Transparent and colorless DSSCs featuring thienyl-pyrrolopyrrole cyanine sensitizers

Thanks to their red-shifted absorption spectra, thienyl-pyrrolopyrrole cyanine sensitizers are an appealing class of dyes for transparent dye sensitized solar cell technology.

Acid-triggered two-stage superlarge redshift absorption for turn-on type photothermal conversion at the first and second near-infrared window

A series of “turn-on” type NIR materials are developed with two-stage superlarge redshifted absorption in the first and second NIR window under the stimulation of protonation for smart photothermal conversion.

The effect of substituents on the aggregation-induced emission of 9,10-phenanthraquinone-hydrazones

One-step synthesis of six hydrazone derivatives exhibiting red-shifted absorption is reported. The compounds are red-emissive in their solid state with moderate to high quantum efficiency and show AIE properties, supported by DLS and SEM studies.

A red-emitting thiophene-modified BODIPY probe for fluorescence lifetime-based polarity imaging of lipid droplets in living cells.

Intracellular polarity in lipid droplets as well as other organelles may provide useful knowledge about various processes taking place in live cells. Therefore, small fluorophores capable of visualising polarity are undergoing rapid development. In this paper, we report new red-emitting polarity sensitive BODIPY probes that can distinguish between liquid-ordered and liquid-disordered phases and can internalise into lipid droplets of live cells. Our reported probes sense lipid environment not through solvatochromic shift of the fluorescence spectra but through the change in the fluorescence lifetime of their monoexponential decays. This makes them convenient for fluorescence lifetime imaging microscopy. The probes were synthesised by modifying viscosity-sensitive meso-phenyl BODIPY with electron-donating 2-thienyl moieties at the α- and β-positions, significantly red-shifting absorption and fluorescence spectra of the dyes and improving sensitivity to polarity, while suppressing viscosity dependence. Finally, a novel probe - BP OC16 TP2 was suitable for sensing polarity in lipid droplets of live MCF-7 human breast cancer cells. We demonstrated that different chemotherapeutics affected lipid droplet polarity differently: cisplatin had no effect on lipid droplet polarity, whereas paclitaxel, depending on its concentration, either decreased or increased lipid droplet polarity.

Sequence-controlled alternating block polychalcogenophenes: synthesis, structural characterization, molecular properties, and transistors for bromine detection.

Sequence-controlled polychalcogenophenes have attracted much interest in terms of synthesis, structure and function in polymer science. For the first time, we developed a new class of alternating block conjugated copolymers denoted as poly(alt-AB)x-b-(alt-AC)y where both blocks are constituted by an alternating copolymer. 3-Hexylthiophene (S), 3-hexylselenophene (Se) and 3-hexyltellurophene (Te) are used as A, B and C units to assemble three sequence-controlled polychalcogenophenes P(SSe)b(STe), P(SSe)b(SeTe) and P(STe)b(SeTe) which are prepared by adding two different Grignard monomers in sequence to carry out Ni(dppp)Cl2-catalyzed Kumada polymerization. The molecular weight, dispersity, and length of each block (x = y) and main-chain sequence can be synthetically controlled via the catalyst transfer polycondensation mechanism. The polymer structures, i.e. alternating block main chain with high side-chain regioregularity, are unambiguously confirmed by 1H-NMR and 13C-NMR. The optical and electrochemical properties of the polymers can be systematically fine-tuned by the composition and ratio of the chalcogenophenes. From GIWAXS measurements, all the polymers exhibited predominantly edge-on orientations, indicating that the packing behaviors of the alternating block polychalcogenophenes with high regioregularity are inherited from the highly crystalline P3HT. P(SSe)b(STe) exhibited a hole OFET mobility of 1.4 × 10-2 cm2 V-1 s-1, which represents one of the highest values among the tellurophene-containing polychalcogenophenes. The tellurophene units in the polymers can undergo Br2 addition to form the oxidized TeBr2 species which results in dramatically red-shifted absorption due to the alternating arrangement to induce strong charge transfer character. The OFET devices using the tellurophene-containing polychalcogenophenes can be applied for Br2 detection, showing high sensitivity, selectivity and reversibility.

Rational design of non-fullerene acceptors via side-chain and terminal group engineering: a computational study.

We investigated the optoelectronic and photovoltaic properties of three types of acceptor-donor-acceptor-based non-fullerene acceptor (NFA) molecules for organic solar cell (OSC) applications. Density functional theory and its time-dependent variant were employed to compute the quadrupole moment perpendicular to the π-system (Q20), open circuit voltage (VOC), and other relevant solar cell parameters. The role of functionalization in the acceptor unit on the overall device performance was explored by incorporating halogen and methoxy-based electron-withdrawing groups. The electronegativity differences between the halogen atoms and the methoxy group demonstrated contrasting effects on the energy levels, molecular orbitals, and absorption maximum. We observed a trade-off between short-circuit current (JSC) and VOC, which was further substantiated by an inverse correlation between Q20 and VOC. We found an optimum value of Q20 in the range of 80 to 130 ea02 to achieve an optimized solar cell performance. Among the designed systems, Se-derived NFAs with a small band gap, red-shifted absorption maximum, high-oscillator strength, small exciton binding energy, and optimum Q20 turned out to be potential candidates for future applications. These criteria can be generalized to design and screen next-generation non-fullerene acceptors to achieve improved OSC performance.

A fluorescent probe based on an enhanced ICT effect for Hg2+ detection and cell imaging.

The mercury ion (Hg2+) has hindered society to some extent due to its high biological toxicity, and a rapid method for Hg2+ detection is urgently needed. In the present work, two fluorescent probes, YF-Hg and YF-Cl-Hg, were developed. YF-Cl-Hg was produced by introducing an electron-withdrawing substituent (-Cl) into the structure of YF-Hg. The probe YF-Cl-Hg possesses a larger Stokes shift and a more pronounced UV-vis absorption redshift compared to YF-Hg in a pH = 7.4 environment. The reasons for the superior spectral performance of YF-Cl-Hg over YF-Hg were explored by density functional theory (DFT) calculations and UV-vis absorption spectroscopy. Furthermore, the good biocompatibility suggests that YF-Cl-Hg possesses the potential to be a tool for Hg2+ detection in cells.

Ultra-small NIR J-aggregates of BODIPY for potent phototheranostics.

Cancer phototheranostics that combines diagnosis with phototherapy has emerged as a new mode of precise treatment. Nevertheless, taking highly effective phototheranostics into consideration, it is still a tremendous challenge to design multifunctional photothermal agents (PTAs) that combine the features of intensive near-infrared (NIR) absorption/emission, high photothermal conversion efficiency (PCE) and preferable tumor accumulation. Herein, seeking a convenient method to facilitate absorption red-shift, promote the accumulation of drugs in tumors and heighten the PCE appears to be particularly important for cancer theranostics. In this work, heavy-atom-free boron dipyrromethene (BODIPY) was assembled with F127 to fabricate ultra-small J-aggregated nanoparticles (named as BNPs). Compared to free BODIPY, BNPs exhibited 63 nm redshifted absorption, deep-tissue fluorescence imaging, enhanced cellular uptake, preferable tumor accumulation, elevated PCE, excellent photothermal stability and water dispersibility. In vivo experiments demonstrated that BNPs could behave as high-performance tumor fluorescent imaging probes and antitumor PTAs to conduct NIR imaging-guided PTT. This work offers a novel J-aggregated framework on developing robust diagnostic and therapeutic agents.

Enhancing Photoresponse and Photocurrent of Integrated Perovskite/Organic Solar Cells via Layer-by-Layer Processing

Perovskite solar cells have developed rapidly in recent years to almost rival silicon cells. To extend the photoresponse in the near-infrared region, integrated perovskite/organic solar cells (IPOSCs) have been developed. Typically, the organic bulk heterojunction (BHJ) in IPOSCs is built by one-step coating of a mixed solution of a donor and an acceptor. Here, we prepare the BHJ by layer-by-layer (LBL) processing. Compared to the traditional one-step coated IPOSCs (TOS device), the LBL-processed device (LBL device) exhibits a distinctly improved short-circuit current density (JSC) and power conversion efficiency. The TOS device shows a high photoresponse from about 400 to 900 nm, while the LBL device shows a high photoresponse extending to about 950 nm. Further research indicates that the extending photoresponse of the LBL-device is caused by the redshift of absorption of the organic BHJ. Meanwhile, the LBL-processed BHJ exhibits slightly improved carrier extraction and recombination. The introduction of LBL processing provides an approach to broaden the optical absorption range and photoresponse of IPOSCs.

D-π-A structured porphyrin sensitizers for dye-sensitized solar cells

Two porphyrin-based D-[Formula: see text]-A structured dyes of SGT-026 and SGT-027 with different acceptor groups were synthesized and characterized for dye-sensitized solar cells. The structure of SGT-027was designed with a very strong acceptor unit of (5-(naphtho[1,2-c:5,6-c[Formula: see text]]bis[1,2,5]-thiadiazolyl)benzoic acid) (NBTD), resulting in more red-shifted absorption bands and broader NIR absorption ability, but SGT-026 porphyrin with a weak acceptor unit of (2-(thieno[3,4-c]pyrrole-4,6(5H)-dionyl)benzoic acid) (TPD) exhibited a blue-shifted Q band absorption, compared to the reference SGT-021dye with a strong acceptor unit of (4-(benzo[c][1,2,5]thiadiazol-4-yl)benzoic acid) (BTD). The photophysical properties of these D-[Formula: see text]-A structured porphyrin sensitizers depend on the degree of the intramolecular charge transfer character with the electron-withdrawing ability order of NBTD> BTD> TPD. The photovoltaic performances were evaluated using cobalt (II/III)-based redox electrolyte, SGT-027 reached a power conversion efficiency (PCE) of up to 7.5%, which was surprisingly inferior to the benchmark porphyrin sensitizer SGT-021 with a PCE of 10.9%, and a PCE of 5.9% was exhibited by SGT-026, under AM 1.5G sunlight. The optical, and electrochemical properties and DFT calculations were utilized to understand the cell performance difference between SGT-dyes.

π-Extended Rubrenes via Dearomative Annulative π-Extension Reaction.

Among a large variety of organic semiconducting materials, rubrene (5,6,11,12-tetraphenyltetracene) represents one of the most prominent molecular entities mainly because of its unusually high carrier mobility. Toward finding superior rubrene-based organic semiconductors, several synthetic strategies for related molecules have been established. However, despite its outstanding properties and significant attention in the field of materials science, late-stage functionalizations of rubrene remains undeveloped, thereby limiting the accessible chemical space of rubrene-based materials. Herein, we report on a late-stage π-extension of rubrene by dearomative annulative π-extension (DAPEX), leading to the generation of rubrene derivatives having an extended acene core. The Diels-Alder reaction of rubrene with 4-methyl-1,2,4-triazoline-3,5-dione occurred to give 1:1 and 1:2 cycloadducts which further underwent iron-catalyzed annulative diarylation. The thus-formed 1:1 and 1:2 adducts were subjected to radical-mediated oxidation and thermal cycloreversion to furnish one-side and two-side π-extended rubrenes, respectively. These π-extended rubrenes displayed a marked red shift in absorption and emission spectra, clearly showing that the acene π-system of rubrene was extended not only structurally but also electronically. The X-ray crystallographic analysis uncovered interesting packing modes of these π-extended rubrenes. Particularly, two-side π-extended rubrene adopts a brick-wall packing structure with largely overlapping two-dimensional face-to-face π-π interactions. Finally, organic field-effect transistor devices using two-side π-extended rubrene were fabricated, and their carrier mobilities were measured. The observed maximum hole mobility of 1.49 × 10-3 cm2V-1 s-1, which is a comparable value to that of the thin-film transistor using rubrene, clearly shows the potential utility of two-side π-extended rubrene in organic electronics.

Synthesis, Properties, and Photovoltaic Characteristics of Fluoranthenedione-containing Nonfullerene Acceptors for Organic Solar Cells

The progress of organic solar cells (OSCs) largely depends on the development of nonfullerene acceptors (NFAs) based on electron-accepting π-conjugated compounds. Therefore, the creation of its building unit is important to tune the properties and increase the OSC performance. In this contribution, a new electron-accepting building unit, fluoranthenedione (FDO), was designed by extending the π-conjugation of representative indene-1,3-dione (IDO) framework. The electron-accepting π-conjugated compound (FL-FDO) composed of thiophene-linked fluorene (FL) as a central unit and FDO as terminal units was designed and synthesized. Compared to the corresponding IDO-containing NFAs, the introduction of FDO led to the red-shifted absorption and increased frontier orbital energy levels. The OSCs based on FL-FDO and poly(3-hexylthiophene) (P3HT) as a donor showed improved power conversion efficiency, compared to the P3HT/FL-IDO-based devices. These results indicate that the FDO unit has the potential to act as a promising terminal unit of NFAs.

Copper-catalyzed α-selective cross-dehydrogenative coupling of BODIPY dyes with aldehydes: A new route to acylated BODIPYs and dipyrromethenes

A novel copper-catalyzed direct acylation of BODIPYs with aldehydes via C–H bond activation was developed, in which acyl radicals were formed from aldehydes in the presence of TBHP as radical initiator, and selectively reacted with BODIPYs at the α-positions. This radical oxidative dehydrogenative cross-coupling reaction showed excellent functional group tolerance, and both heteroaromatic and aliphatic aldehydes could be effectively reacted to BODIPYs. Comparing with those of the corresponding starting BODIPYs, those α-acylated BODIPYs showed red-shifted absorption and emission, as well as decreased both HOMO and LUMO energies due to the installation of electron-deficient carbonyl groups. Furthermore, the α-acylated BODIPY provided an efficient access to α-acylated dipyrrin by removal of the BF2 protecting groups, which showed sensitive and selective “turn-on” fluorescence response toward Zn2+ ion in aqueous buffer solution and living cells.