Enhancement of Palladium‐Porphyrin Room Temperature Phosphorescence by Alkaline Earth Metal in Deoxycholate Aggregates Solution

Experimental Verification of the Accuracy of Oxygen-Varying Correlated Fluorescence for Determining the Quenching Constant KSV

The oxygen-varying correlated fluorescence provides an effective strategy to gain the quenching constant KSV for a non-phosphorescent system. Owing to the absence of detectable phosphorescence emission in general optical spectroscopy, the facticity of this method has never been verified. Here, the correct way to determine KSV by oxygen-varying correlated fluorescence was systematically studied in detail. We selected gadolinium protoporphyrin IX (Gd-PpIX) to establish a fluorescence and phosphorescence dual emission system. Then, KSV of Gd-PpIX can be obtained by the change of fluorescence intensity (IF) with oxygen concentration using the method of correlated fluorescence at intense pump power; meanwhile, the value can also be determined from the relationship of the phosphorescence intensity ratio and oxygen content by the Stern-Volmer equation under relatively low power density. It was found that the KSV values obtained by the above two methods were 12.2(1) and 11.9(7) kPa-1, respectively. Our results successfully verified the accuracy of oxygen-varying correlated fluorescence for determining the KSV by the phosphorescence property and fluorescence saturation of Gd-PpIX.

Insight into the Heavy Atom Effect Induced by Environmental Heavy Atoms for Gadolinium-Labeled Hematoporphyrin Monomethyl Ether

Environmental heavy atoms can further enhance the room temperature phosphorescence (RTP) emissions of gadolinium-labeled hematoporphyrin monomethyl ether (Gd-HMME) by way of the external heavy atom effect (HAE). However, the macroscopic phosphorescence intensity covered the intrinsic effect of the environmental heavy atoms. In this study, a method of separating the external HAE from the total is performed, and a quantity to describe the intrinsic nature of external HAE is defined. The environmental Gd³⁺ concentration evolution of the phosphorescent transition rate (k_P) is obtained by correlated absorption, emission, and time-resolved spectroscopy. The k_P increases linearly with environmental Gd³⁺ concentration, while the intercept k_P0 coincides with that of the internal HAE. The slope κ could be calculated, and it is a quantity free of the Gd³⁺ concentration and only relies on the type of environmental heavy atoms. In addition, the environmental Lu³⁺ exhibits similar functionality to Gd³⁺ in external HAE. Environmental Pd²⁺ quenches the phosphorescence intensity macroscopically, while it enhances the HAE intrinsically. Our method provides an alternative insight into the intrinsic nature of environmental heavy atoms.

Oxygen-Varying Correlated Fluorescence for Determining the Stern-Volmer Constant of Porphyrin

The achievement of the Stern-Volmer constant (K_SV) of porphyrin, a parameter to describe the ability of energy transfer to oxygen, enables us to understand and engineer the functionalities of porphyrin. In this study, we propose a new method to obtain K_SV by steady fluorescence based on the population correlation between the excited triplet state (T₁) and the singlet excited state (S₁). Nonlinear fluorescence intensity of porphyrin [hematoporphyrin monomethyl ether (HMME)] as a function of pump power is observed, and this nonlinearity is oxygen-concentration-dependent. These observations originated from the population correlation, where more intense pump power introduces a stronger population correlation. Most importantly, we have found that the oxygen content can influence this correlation via the quenching of T₁ based on its sequent change of fluorescence intensity; K_SV ∼ 28 kPa^-1 can be obtained theoretically for HMME. Our investigation not only offers a promising method of achieving K_SV conveniently by steady fluorescence but also enlightens the advances of regulable fluorescence correlation.

Tailor-Made Polymer Nano-Assembly with Switchable Function and Amplified Anti-Tumor Therapy

The difficulty in killing tumor cells due to the tendency to metastasis and drug resistance are outstanding and urgent problems for the treatment of cancer. It is imperative to figure out an effective therapy strategy to break the treatment dilemmas. Nano self-assembly has the characteristics of flexible regulation, biological compatibility, and easy access. Herein, an albumin-polymer nano-assembly with switchable cytotoxicity and reactive oxygen species (ROS) amplification capability is developed for anti-tumor therapy. The nano-assembly (PFFBT@HSA) is comprised of conjugated polymer PFFBT and natural protein human serum albumin (HSA) via the hydrophobic and electrostatic interactions. The innovative switchable strategy is proposed and realized by HSA turning off the cytotoxicity of PFFBT and then turning on and enhancing the cytotoxicity by generating massive ROS upon light irradiation. The combination of HSA provides more stable microenvironment to benefit the generation of highly effective anti-tumor model of "0+1>1". These results display that the nanostructured self-assembly and the proposed anti-tumor regulation strategy are effective, which will contribute to the diversified treatment of cancer.

Enhanced oxygen sensing sensitivity by eliminating the protection of triplet phosphorescence

High oxygen sensitivity (the slope of the Stern-Volmer plot reaches 0.73/μM) is achieved with a phosphorescence indicator, gadolinium-hematoporphyrin monomethyl ether (Gd-HMME), by decreasing the extent of its protection. In air-saturated solution, the phosphorescence quantum efficiency (QE) of Gd-HMME in a non-rigid microenvironment is lower than that in a rigid microenvironment. In contrast, when oxygen is removed, the QE of Gd-HMME in the non-rigid microenvironment was found to be same as that of Gd-HMME in the rigid microenvironment. This indicates that Gd-HMME is much more sensitive to oxygen in the non-rigid microenvironment. The oxygen sensitivity of Gd-HMME was found to increase as the rigidity of its microenvironment decreases. The oxygen response of Gd-HMME without any protection reaches 240 (0-374 μM oxygen), whereas that in the rigid microenvironment is only 3 in this range. The measurement precision of Gd-HMME without any protection is lower than that in the rigid microenvironment. These results indicate that the measurement of oxygen in different concentration ranges would require the rigidity of the microenvironment to be varied. Gd-HMME without any protection can be applied to detect oxygen as low as 0.1 μM. The detection limit of oxygen was evaluated to be as low as 20 nM based on Gd-HMME without any protection.

Al3+ enhanced room temperature phosphorescence of Pd-porphyrin resided in hybrid supramolecular gels and used for detection of trace Hg2+ ions

Micelle-hybridized supramolecular hydrogels were constructed through the self-assembly of gelator N,N-dibenzoyl-L-cystine (DBC) and micelles formed from a Gemini surfactant (G_12-8-12). A phosphor, palladium meso-tetra (4-carboxyphenyl) porphyrin (Pd-TCPP) and Al³⁺ ions were loaded within the hybrid system. Interestingly, the room temperature phosphorescence (RTP) of Pd-TCPP can be efficiently enhanced and modulated by the concentration of Al³⁺ ions. The enhancement effect could be attributed to the interactions between Al³⁺ and DBC as well as porphyrin, which verified by ¹H NMR analysis. The study of transmission electron microscopy and scanning electron microscopy indicated that a more compact 3D network structure of the gel system was formed upon the addition of Al³⁺. In addition, measurement of critical micelle concentration indicated that Al³⁺ ions increase the surface activity of G_12-8-12 to promote micelle formation, thereby increasing the dispersion of Pd-TCPP in the hybrid gels. Based on the synergistic effect of these results, the non-radiative transition of Pd-TCPP was efficiently inhibited, resulting in highly efficient RTP. Furthermore, the enhanced RTP of as-prepared gel system shows potential application to detect trace Hg²⁺ ions because the RTP can be quenched by Hg²⁺. A linear relationship between RTP against the logarithmic concentration of Hg²⁺ was found over the range of 6 × 10^-8 and 1 × 10^-6 mol/L. The detection limit was found to be 0.017 nmol/L.

The effect of imidazole on the enhancement of gadolinium-porphyrin phosphorescence at room temperature

The mechanism for the 40-fold enhancement in Gd-HMME RTP intensity by adding imidazole and Gd³⁺ is revealed.

Protection of densely populated excited triplet state ensembles against deactivation by molecular oxygen

Different approaches towards protection of triplet excited states against deactivation by molecular oxygen are summarized and reviewed.