Investigation into the Oxygen-Involved Electrochemiluminescence of Porphyrins and Its Regulation by Peripheral Substituents/Central Metals.

We provide evidence of oxygen-involved electrochemiluminescence (ECL) of metal-free porphyrins and metalloporphyrins first. O2•- and OH•, which are oxygen intermediates, are indispensable for the formation of excited porphyrins, which has been proven by trapping free radical strategies. The wide differences regarding emission location and mechanism between metal-free porphyrins [including meso-tetra(4-methoxyphenyl)porphine (H2TMPP), meso-tetraphenylporphyrin (H2TPP), and meso-tetra(4-carboxyphenyl)porphine (H2TCPP)] and metalloporphyrins (MTPP) depend on whether protons are present in the center of the porphin ring. Besides, the oxygen-involved ECL of porphyrins can be controlled regularly by peripheral substituents with different polarities. Because of the stretched molecular structure and the decrease in electron density around the protons located at porphin ring, electron-withdrawing groups are more conducive to protons being attacked by O2•-, as well as the enhancement of porphyrins ECL. The ECL efficiency [ΦECL, which is normalized with respect to Ru(bpy)3(PF6)2 (taking ΦECL of Ru(bpy)3(PF6)2 = 1)] is gradually improved from H2TMPP (ΦECL = 0.16), to H2TPP (ΦECL = 2.20), to H2TCPP (ΦECL = 3.83); the ΦECL = 4.21 of Zn(II)TPP is significantly higher than those of other MTPPs [e.g., Co(II)TPP and Cu(II)TPP]. A deeper understanding regarding the improvement of porphyrins ECL efficiency and new application toward porphyrins-related devices can be achieved from this work.

J-Aggregates of zinc tetraphenylporphyrin: a new pathway to excellent electrochemiluminescence emitters.

Low-potential electrochemiluminescence (ECL) luminophores with excellent ECL behavior have attracted considerable interest in biological analysis. Herein, we explored the ECL behavior of ZnTPP with different aggregates for the first time. In this work, we used the mixed solvent method to prepare the H- and J-aggregates of zinc tetraphenylporphyrin (ZnTPP). This resulted in a completely disparate morphology, such as nanoparticles and rod-aggregates, which were observed by recording atomic force microscopy (AFM) images. Characteristic changes in the optical properties and electrochemical properties of ZnTPP appeared when it underwent H- and J-aggregation. Significantly, the measured ECL behavior varied for the same ZnTPP molecules when they were in the form of H- and J-aggregates; and the ECL intensity of the J-aggregates was more than ten times that of the H-aggregates due to a narrower band gap and the formation advantages in J-aggregates. The narrower band gap of J-aggregates not only facilitates the electron-hole pair recombination, but also facilitates the electron injection into the J-aggregates. The formation advantage of the J-aggregates is likely to contribute to the strong ECL intensity of the J-aggregates. Maybe the big number of ZnTPP molecules in a J-aggregate unit increases the opportunity of generating excited states and light from excited state radiation. The ECL property could be regulated with the different aggregation of ZnTPP, which led to a decline of ECL cathode potential in the J-aggregates (191 mV) compared with the H-aggregates. This work provides an effective and novel strategy for developing ECL emitters with low potential and high ECL emission intensity via adjusting aggregation motifs.

Electrochemiluminescence Platforms Based on Small Water-Insoluble Organic Molecules for Ultrasensitive Aqueous-Phase Detection.

Highly efficient detection in the aqueous phase for water-insoluble organic molecule probes is challenging. The bright aggregated-state electrochemiluminescence (ECL) of 1,1-disubstituted 2,3,4,5-tetraphenylsiloles by a co-reactant approach was discovered, and a heterogeneous aggregation-induced emission ECL (HAIE-ECL) was constructed at the electrode surface, showing very high ECL efficiency (37.8 %) and selective recognition for industrially important DNBP plasticizer with a low detection limit of 0.15 nm in the water phase. A mechanistic study indicates that ECL is mainly generated due to the high electron affinity of siloles and restriction of the intramolecular motions caused by their propeller-like noncoplanar structures. This system realizes the sensing of organic-based ECL in the water phase by solving the crucial problems of water insolubility and aggregation-caused quenching (ACQ), and demonstrates potential for further application because of its design and high efficiency.

Bimodal Electrochemiluminescence of G-CNQDs in the Presence of Double Coreactants for Ascorbic Acid Detection.

How to improve the accuracy of target detection substance in low-content and complex of real sample, which is still a major challenge in the analysis field. There is no doubt that the internal standard method is the best choice in the analysis methods. The internal standard method of ECL strategy can furnish more accurate detection results in the changeable complex environment, and it can dispel the primary vaguest interference in the system through the self-calibration of two emission spectra. Herein, we effectually explored a strong and stable bimodal ECL system based on graphitic carbon nitride quantum dots (g-CNQDs) as single luminophore in the presence of double coreactants potassium persulfate (K2S2O8) and tetrabutylammonium bromide (TBAB) under the optimized conditions. ECL-1 at 2.82 V and ECL-2 at 1.73 V were observed when the potential was scanned between -3 and 3 V at the scan rate of 0.2 V·s-1. The ECL-1 was responding to the analyte, that is, ascorbic acid (AA) and the ECL-2 was not for a certain concentration of AA; hence, the developed bimodal ECL system was used as internal standard method for quantitative AA in human serum due to the different sensitivity of the double-peak ECL signals to the target analytes. The linear relationships were obtained based on the ln I (ECL-1/ECL-2) against the concentration of AA in the concentration range of 3.5 to 330 nM, with a detection limit of 110 pM (S/N = 3).

Development of stimuli responsive polymeric nanomedicines modulating tumor microenvironment for improved cancer therapy.

The complexity of the tumor microenvironment (TME) severely hinders the therapeutic effects of various cancer treatment modalities. The TME differs from normal tissues owing to the presence of hypoxia, low pH, and immune-suppressive characteristics. Modulation of the TME to reverse tumor growth equilibrium is considered an effective way to treat tumors. Recently, polymeric nanomedicines have been widely used in cancer therapy, because their synthesis can be controlled and they are highly modifiable, and have demonstrated great potential to remodel the TME. In this review, we outline the application of various stimuli responsive polymeric nanomedicines to modulate the TME, aiming to provide insights for the design of the next generation of polymeric nanomedicines and promote the development of polymeric nanomedicines for cancer therapy.