Near-Infrared Light and Acid/Base Dual-Regulated Polymerization Utilizing Imidazole-Anion-Fused Perylene Diimides as Photocatalysts

Unraveling the Roles of Amines in Atom Transfer Radical Polymerization in the Dark

Multidentate amines have been widely used as ligands (L) for Cu-catalysts in atom transfer radical polymerization (ATRP) and as electron donors in photochemically induced polymerizations. However, mechanistic aspects of the role of amines in ATRP in the dark have remained elusive. Herein, the structure-activity relationship and the related electron transfer reactions with Br-CuII/L complexes and/or with alkyl bromides (R-Br) were investigated for 25 amines. Amines function as electron donors and reducing agents for Br-CuII/L complexes via an outer sphere electron transfer (OSET) mechanism, enabling slow but continuous generation of CuI/L activators and inducing controlled ATRP. However, two amines, diazabicyclo(5.4.0)undec-7-ene (DBU) and 1,1,3,3-tetramethylguanidine (TMG), reduced Br-CuII/L faster, suggesting an inner sphere electron transfer (ISET) process. ATRP, starting with initial deactivators (Br-CuII/L) species, proceeded in the dark in the presence of an excess of tertiary amines, such as tris[2-(dimethylamino)ethyl]amine (Me6TREN), 1,4-diazabicyclo[2.2.2]octane (DABCO), and TMG at room temperature and afforded polymers with low dispersities (Đ ≤ 1.15). With copper(II) triflate complex (CuII/L+2, -(OTf)2), which has a more positive reduction potential, ATRP proceeded at room temperature with several inexpensive secondary and tertiary amines including triethylamine (TEA) and dimethylethanolamine (DMAE). Interestingly, multidentate amines also served as direct R-Br activators at elevated temperatures (60 °C). In all cases, chains were initiated with R-Br and not by the amine radical cations as byproducts of electron transfer. Amines also enabled ATRP in the presence of residual air in flasks with a large headspace, underpinning them as a robust and accessible reducing agent for practical applications.

Photoinduced Stable Circularly Polarized Luminescent Radicals From a Triphenylamine-Attached Planar Chiral Pillar[5]Arene

Photoinduced organic radicals with unique luminescent properties are highly sought-after due to their important prospects in synthetic chemistry and materials science. However, the current development of organic free radicals, including photoinduced ones, is significantly limited and faces challenges related to stability and poor luminescence behavior. Taking advantage of the photoelectric activity of triarylamine, we herein describe an unusual luminescent radical, which can be rapidly generated by UV irradiation of a solid-state triarylamine-functionalized π-conjugated pillar[5]arene (EtP5NN) in air, accompanied by luminescent color switching from bluish-violet to sky-blue. The persistent radicals within EtP5NN with a half-life of 12.7 h suggest that the pillar[5]arene skeleton straightforwardly improves the stability of radicals. The sterically bulky triarylamine groups inhibit the racemization of planar chiral pillar[5]arene and allow the optical resolution of this system. The enhancement of circularly polarized luminescence (CPL) is triggered by UV irradiation of the enantiomers (pS/pR-EtP5NN) in the solid state.

Catalase-like activity of perylene diimide based radical anion: Chromogenic substrate for achieving glucose sensing

In this work, perylene diimide based radical anion (PH2-) is synthesized and characterized using optical, NOBF4 methods; cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. The PH2- is stable for 120 min (2 h) in oxygenated environment and 273 min (4.5 h) in hypoxic conditions. The PH2- showed catalase-like activity to reduce H2O2 to H2O with turn-over number (TON) = 20 and turn-over frequency (TOF) = 40 h-1. The catalase-like activity can be measured using optical and electrochemical methods by monitoring the changes at 726 nm (absorbance); 585 nm (emission) and at 0.27 V. We were able to quantitatively monitor the ultra low-level concentrations of the H2O2 as low as 320 fM (absorbance) and 200 fM (emission). Moreover, PH2- could be used as a chromogenic and fluorogenic substrate for monitoring the low-level concentrations of the glucose using GOx based biochemical assay. We have demonstrated the development and validation of the glucose assay kit for the detection of glucose as low as 3.6/2.8 nM in aqueous medium and 6.2/5.6 nM in blood serum.

Better Together: Photoredox/Copper Dual Catalysis in Atom Transfer Radical Polymerization

Photomediated Atom Transfer Radical Polymerization (photoATRP) is an activator regeneration method, which allows for the controlled synthesis of well-defined polymers via light irradiation. Traditional photoATRP is often limited by the need for high-energy ultraviolet or violet light. These could negatively affect the control and selectivity of the polymerization, promote side reactions, and may not be applicable to biologically relevant systems. This drawback can be circumvented by an introduction of the catalytic amount of photocatalysts, which absorb visible and/or NIR light and, therefore, controlled, regenerative ATRP can be performed with the dual-catalytic cycle. Herein, a critical summary of recent developments in the field of dual-catalysis concerning Cu-catalyzed ATRP is provided. Contributions of involved species are examined mechanistically, followed by challenges and future directions towards the next generation of advanced functional macromolecular materials.

Modified perylene diimide for femto molar level detection of glucose: smartphone-assisted colorimetric glucose detection kits

In this report, a functionalized hydroxyphenyl benzothiazole (HBT) derivative has been synthesized and anchored onto the perylene diimide (PDI) core at the -bay position (PHI). PHI has been explored for the generation of radical anions (PH1˙-) and dianions (PH12-) in 20% HEPES buffer-DMSO solution using H2S as a sacrificial electron donor. The PH1˙- has a half-life (t1/2) of 1.5 h and 3 h in oxygenated and hypoxic conditions, respectively. The formation of radical anions has been confirmed by optical (absorbance and fluorescence) methods, cyclic voltammetry (CV), differential pulse voltammetry (DPV), and femtosecond transient absorbance spectroscopy along with current-voltage (I-V) and NOBF4 studies. The PH1˙- showed peroxidase-like activity for the reduction of H2O2 as low as 170 fmol L-1 (fM) giving a colour change from sea green to pink. The biochemical assay which consists of PH1˙-+ GOx has been further utilized as a glucose sensor. Upon addition of glucose (0-8 nM) in the biochemical assay, the in-situ produced H2O2 (after oxidation of glucose with GOx) oxidized PH1˙- to PH1 giving a sea green to pink colorimetric read out along with a decrease in the absorption intensities at 720, 815, 880 and 950 nm and the emergence of absorption intensity at 541 nm. The lowest limit of detection is 85 fM. We also explored this biochemical assay for the detection of 860 fM of glucose in a 10% blood serum. Similarly, fluorometric, CV and DPV studies were carried out for the detection of glucose using this biochemical assay. The smartphone-assisted RGB colour analyser showed large variations in the red colour and this RGB based colour differentiation can be used for the detection of 1 nM of glucose.

Photochemical Action Plots Reveal Red-shifted Wavelength-dependent Photoproduct Distributions

Photochemical action plots are a powerful tool for mapping photochemical reaction outcomes wavelength-by-wavelength. Typically, they map either the depletion of a reactant or the formation of a specific product as a function of wavelength. Herein, we exploit action plots to simultaneously map the formation of several photochemical products from a single chromophore. We demonstrate that the wavelength-resolved mapping of two reaction products formed during the irradiation of a chalcone species not only shows wavelength dependence - exhibiting the typical strong red-shift of the photochemical reactivity compared to the absorbance spectrum of the chromophore - but also a strong wavelength selectivity with remarkably different product distributions resulting from different irradiation wavelengths.