Ethylenediamine-modified graphene oxide covalently functionalized with a tetracarboxylic Zn(ii) phthalocyanine hybrid for enhanced nonlinear optical properties

Electron transfer-mediated synergistic nonlinear optical response in the Agn@C18 (n = 4-6) complexes: A DFT study on the electronic structures and optical characteristics

Seeking highly efficient and stable non-linear optical (NLO) materials is crucial yet challenging, given their promising applications in laser diodes and photovoltaics. In this study, we employ the excess electron and charge transfer strategies to theoretically design three novel complexes, namely Agn@C18 (n = 4-6), by adsorbing silver clusters onto the cyclo[18]carbon ring (C18). Our aim is to investigate the NLO characteristics of these complexes using density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. The results reveal that the adsorption of Ag clusters onto C18 leads to a decrease in excitation energy and an increase in dipole moment and oscillator strengths, thereby significantly enhancing the hyperpolarizability of the complexes. Strikingly, among all these complexes, Ag6@C18 exhibits the highest first hyperpolarizability value of approximately 109496.2620 au calculated at the B3LYP/cc-PVDZ-pp level of theory, which is about 1.3 × 106 times higher than that of pure C18. This finding validates the effectiveness of the proposed strategies in enhancing the NLO response of the species. Moreover, the calculated UV-Vis absorption spectrum demonstrates that the Agn@C18 complexes with excess electrons exhibit absorption at longer wavelengths (ranging from 385 to 731 nm) compared to C18. In addition, the stability, chemical bonding, and charge transfer characteristics of the Agn@C18 (n = 4-6) complexes were also discussed. These findings highlight the potential of these complexes for the development of highly efficient NLO devices.

Synthesis of Multicolor Carbon Dots Catalyzed by Inorganic Salts with Tunable Nonlinear Optical Properties

The nonlinear optical properties of carbon dots have been in the spotlight in recent years. In light of the complexity and diversity of factors affecting the nonlinear optical properties of carbon dots, how to reveal the origin and physical mechanism of the nonlinear optical properties of carbon dots accurately has become a problem. In this work, a template-free method was designed to prepare carbon dots via solid-phase reaction with phloroglucinol as a single carbon source and sodium bisulfate as the catalyst. This method is simple, green, safe, and easy to be prepared on a large scale. Three carbon dots with different luminous colors were obtained by simply adjusting the reaction temperature. The rise of reaction temperature affects the surface functional groups, and then hinders the luminescence of surface states, leading to the change of luminescence properties. The nonlinear optical properties of carbon dots were analyzed by the Z-scan technique. Surprisingly, all carbon dots have nonlinear optical responses, but there are differences in performance. Results prove the increase in sp2 domains may contribute to the significant improvement of the nonlinear optical properties of carbon dots, indicating a direction to improve the nonlinear optical properties of carbon dots.

Graphene Oxide/Cholesterol-Substituted Zinc Phthalocyanine Composites with Enhanced Photodynamic Therapy Properties

In the present work, cholesterol (Chol)-substituted zinc phthalocyanine (Chol-ZnPc) and its composite with graphene oxide (GO) were prepared for photodynamic therapy (PDT) applications. Briefly, Chol-substituted phthalonitrile (Chol-phthalonitrile) was synthesized first through the substitution of Chol to the phthalonitrile group over the oxygen bridge. Then, Chol-ZnPc was synthesized by a tetramerization reaction of Chol-phthalonitrile with ZnCl2 in a basic medium. Following this, GO was introduced to Chol-ZnPc, and the successful preparation of the samples was verified through FT-IR, UV-Vis, 1H-NMR, MALDI-TOF MS, SEM, and elemental analysis. Regarding PDT properties, we report that Chol-ZnPc exhibited a singlet oxygen quantum yield (Φ∆) of 0.54, which is slightly lower than unsubstituted ZnPc. Upon introduction of GO, the GO/Chol-ZnPc composite exhibited a higher Φ∆, about 0.78, than that of unsubstituted ZnPc. Moreover, this enhancement was realized with a simultaneous improvement in fluorescence quantum yield (ΦF) to 0.36. In addition, DPPH results suggest low antioxidant activity in the composite despite the presence of GO. Overall, GO/Chol-ZnPc might provide combined benefits for PDT, particularly in terms of image guidance and singlet oxygen generation.

Geometric, Electronic, and Optoelectronic Properties of Carbon-Based Polynuclear C3O[C(CN)2]2M3 (where M = Li, Na, and K) Clusters: A DFT Study

Carbon-based polynuclear clusters are designed and investigated for geometric, electronic, and nonlinear optical (NLO) properties at the CAM-B3LYP/6-311++G(d,p) level of theory. Significant binding energies per atom (ranging from -162.4 to -160.0 kcal mol^-1) indicate excellent thermodynamic stabilities of these polynuclear clusters. The frontier molecular orbital (FMOs) analysis indicates excess electron nature of the clusters with low ionization potential, suggesting that they are alkali-like. The decreased energy gaps (E_H-L) with increased alkali metals size revael the improved electrical conductivity (σ). The total density of state (TDOS) study reveals the alkali metals' size-dependent electronic and conductive properties. The significant first and second hyperpolarizabilities are observed up to 5.78 × 10³ and 5.55 × 10⁶ au, respectively. The β_o response shows dependence on the size of alkali metals. Furthermore, the absorption study shows transparency of these clusters in the deep-UV, and absorptions are observed at longer wavelengths (redshifted). The optical gaps from TD-DFT are considerably smaller than those of HOMO-LUMO gaps. The significant scattering hyperpolarizability (β_HRS) value (1.62 × 10⁴) is calculated for the C3 cluster, where octupolar contribution to β_HRS is 92%. The dynamic first hyperpolarizability β(ω) is more pronounced for the EOPE effect at 532 nm, whereas SHG has notable values for second hyperpolarizability γ(ω).

Safety assessment of new nanodiamonds@corrole hybrids addressed by the response of RAW-264.7 macrophages

Safety assessment of carbon nanomaterials is of paramount importance since they are on the frontline for applications in sensing, bioimaging and drug delivery. The biocompatibility and safety of functionalized nanodiamonds (NDs) are here addressed through the study of the pro-inflammatory response of RAW-264.7 macrophages exposed to new nanodiamonds@corrole hybrids. The corrole unit selected is as a prototype for a hydrophobic organic molecule that can function as a NIR fluorophore reporter, an optical sensor, a photodynamic therapy agent or a photocatalyst. The new functional nanohybrids containing detonated nanodiamonds (NDs) were obtained through esterification using carboxylated NDs and glycol corroles. The success of the covalent functionalization via carbodiimide activation was confirmed through X-ray photoelectron spectroscopy (XPS), Raman and Fourier transform infrared (FTIR) spectroscopy. The UV-vis absorption and emission spectra of the hybrids are additive with respect to the corrole features. The cellular uptake, localization, cell viability and effects on immune cell activation of the new hybrids and of the precursors were carefully investigated using RAW-264.7 macrophages. Overall results showed that the ND@corrole hybrids had no pro-inflammatory effects on the RAW-264.7 macrophage cell line, making them an ideal candidate for a wide range of biomedical applications.

Photodynamic therapy characteristics of phthalocyanines in the presence of boron doped detonation nanodiamonds: Effect of symmetry and charge

The synthesis, photophysicochemical and photodynamic therapy (PDT) activity of benzothiazole substituted zinc phthalocyanine: 1 (asymmetrically substituted and composed of no charges), 2 (asymmetrically substituted and composed of three positive charges), and 3 (symmetrically substituted and composed of four positive charges), are presented. The triplet and singlet oxygen quantum yields were highest for complex 2 showing the importance of asymmetry and charge. The complexes are covalently and non-covalently linked to B doped detonation nanodiamonds (B@DNDs) to yield nanohybrids (B@DNDs-1, B@DNDs-2, B@DNDs-3). The presence of B@DNDs, asymmetry and positive charge resulted in improved PDT with the lowest cell viability being observed for B@DNDs-2 at 5%. The cell viability ranged from 5 to 7% for the nanohybrids compared to 19 to 26% for Pcs alone.

Photodynamic antimicrobial activity of benzimidazole substituted phthalocyanine when conjugated to Nitrogen Doped Graphene Quantum Dots against Staphylococcus aureus

In this study, peripherally benzimidazole unit substituted ZnPc (1) and its conjugation to nitrogen doped graphene quantum dot (NGQD) as potential phthalocyanine support via π-π stacking have been presented and fully characterized. The bottom-up solution-based synthesized NGQDs was conjugated non-covalently to zinc phthalocyanine to form NGQDs-Pc nanoconjugates. The photophysical and photochemical properties of both such as absorption, fluorescence, fluorescence life time, singlet oxygen quantum yields, triplet state quantum yields and exited state lifetimes were investigated in solutions. We observed a decrease in the fluorescence quantum yields with a corresponding increase in the triplet quantum yield and singlet oxygen quantum yield of the nanoconjugates in comparison to the phthalocyanine complex alone. Photodynamic antimicrobial chemotherapy activities (PACT) of ZnPc alone and its nanoconjugate were determined towards Staphylococcus aureus.

Oxacarbon superalkali C3X3Y3 (X = O, S and Y = Li, Na, K) clusters as excess electron compounds for remarkable static and dynamic NLO response

An intriguing class of excess electron oxacarbon superalkali clusters is explored for nonlinear optical response through density functional theory (DFT) methods at CAM-B3LYP/6-311++G(d,p). These superalkali clusters shows noticeable binding energies per atom (E_b) which reveals their thermodynamic stabilities (-86.45 ∼ -119.44 kcal mol^-1). The obtained significant VIPs values also suggest the electronic stability of these clusters. The VIP values range from 2.06 eV to 3.42 eV. These clusters show remarkable electronic properties and their HOMO-LUMO gaps (E_H-L) are significantly reduced. The lowest H-L gap of 0.96 eV is obtained for C₃O₃K₃ while the highest H-L gap of 2.07 eV is calculated for C₃S₃Li₃. The obtained PDOS spectra further provide evidence for the superior electronic properties of these clusters. The clusters show excellent nonlinear optical properties as revealed from remarkable values (1.6 × 10⁶ au) of static first hyperpolarizability. The controlling factors for hyperpolarizability are also explored by using conventional two-level model. The calculated values of β_o are correlated nicely with β_tl. The crucial excitation energy is the key factor in controlling the first hyperpolarizability. In these excess electron clusters, the second hyperpolarizability (γ_o) response increases up to 4.3 × 10⁹ au. Moreover, the calculated scattering hyperpolarizability (β_HRS) values are quite significant in these clusters and the highest value of 1.3 × 10⁶ au is calculated for C₃S₃K₃. Additionally, these clusters also possess larger dynamic nonlinearities. The dynamic second hyperpolarizability with dc-Kerr effect increases up to 1.0 × 10¹¹ au. The remarkable values for refractive index (n₂) also suggest the excellent nonlinearity of these superalkali clusters.

Detonation nanodiamonds-phthalocyanine photosensitizers with enhanced photophysicochemical properties and effective photoantibacterial activity

The nanophotosensitizers based on acetophenoxy tetrasubstituted metallophthalocyanines (MPc) and detonation nanodiamonds (DNDs) were successfully formed and their photophysicochemical properties were determined. The zinc(II)Pc and indium(III)Pc complexes along with their nanoconjugates were found to have high singlet oxygen quantum yields (0.72 - 0.84) associated with the heavy central metal effect. The ability of the functional groups present on the DNDs to bind to the bacteria cell and the improved solubility of the nanoconjugates due to DNDs resulted in effective photodynamic antimicrobial therapy (PACT) activity against S. aureus planktonic cells, with the highest log reduction of 9.72 ± 0.02 for the conjugate of InPc conjugate with DNDs after 30 min irradiation. PACT studies were investigated at a dose of 10 μg/mL for each sample. The results suggest that the readily synthesized nanoconjugates can be used as appropriate PACT agents.

A search for enhanced photodynamic activity against Staphylococcus aureus planktonic cells and biofilms: the evaluation of phthalocyanine-detonation nanodiamond-Ag nanoconjugates

The present work reports on the synthesis and characterization of novel zinc (2) and indium (3) 2-amino-4-bromophenoxy substituted phthalocyanines (Pcs) along with the self-assembled nanoconjugates formed viaπ-π stacking interaction onto detonation nanodiamonds (DNDs) to form 2@DNDs and 3@DNDs. 2@DNDs and 3@DNDs were covalently linked to chitosan-silver mediated nanoparticles (CSAg) to form 2@DNDs-CSAg and 3@DNDs-CSAg nanoconjugates. High singlet oxygen quantum yields in DMSO of 0.69 and 0.72 for Pcs alone and 0.90 and 0.92 for 2@DNDs-CSAg and 3@DNDs-CSAg, respectively, were obtained. The photodynamic antimicrobial chemotherapy (PACT) activity of both phthalocyanines and nanoconjugates was tested against planktonic cells and biofilms of S. aureus. 2@DNDs-CSAg and 3@DNDs-CSAg caused effective killing with a log reduction of 9.74. In addition, PACT studies on single-species S. aureus biofilms were carried out with log reduction values of 5.12 and 5.27 at 200 μg mL^-1 for 2@DNDs-CSAg and 3@DNDs-CSAg, respectively.

Hyperbranched lutecium phthalocyanines grafted ethylenediamine@graphene oxide with enhanced nonlinear optical properties

To enhance the nonlinear optical properties of graphene oxide in organic solvent and polymeric matrix, lutecium phthalocyanines (LuPc) and hyperbranched lutecium phthalocyanines (HBLuPc) have been grafted on the surface of graphene oxide, respectively. After the surficial modification, the electron transfer process between phthalocyanines and graphene oxide has been also facilitated, resulting in significant fluorescence quenching. Given the combination of nonlinear scattering, two-photon absorption with reverse saturable absorption and the photo-induced electron or energy transfer from the electron donor (phthalocyanine moiety) to the acceptor (graphene oxide), stronger nonlinear optical properties can be realized based on graphene oxide hybrids compared with graphene oxide and phthalocyanines. Furthermore, graphene oxide hybrid modified by hyperbranched lutecium phthalocyanines exhibits the best optical limiting response and the highest nonlinear extinction coefficient at 532 nm in both organic solvent and polymeric matrix. Interestingly, we also find that it could exhibit better optical limiting properties than those possessed by pure phthalocyanine at 1064 nm.

Sensible graphene oxide differentiates macrophages and Leishmania: a bio-nano interplay in attenuating intracellular parasite

Leishmania is an obligate intracellular protozoan parasite, which resides in human macrophage vacuoles that are referred to as parasitophorus vacuoles. Amphotericin B (AmB) is the first-line drug with 99% cure rates; however, overdose-induced toxic side effects are a major limitation. To improve the efficacy at lower dose and subsequently to avoid toxicity and to further investigate the role of charge dynamics on the efficacy, a graphene oxide (GO)-based composite of AmB was developed with native negatively charged GO and amine-conjugated positively charged AGO. The AGO composite resulted in enhanced uptake as confirmed by confocal and FACS analysis. Thus, AGO caused a strong inhibition of amastigotes, with IC50 values 5-fold lower than free AmB. The parasitophorus vacuoles harbour a hydrolytic and acidic environment, which is favourable for the parasites, as they don't attenuate this condition. AGO-AmB was able to modify the intracellular pH of the Leishmania donovani-infected macrophages, generating unfavourable conditions for the amastigote, and thus improving its efficacy.

Singlet Oxygen Generating Properties of Different Sizes of Charged Graphene Quantum Dot Nanoconjugates with a Positively Charged Phthalocyanine

Various sizes of graphene quantum dots (GQDs) denoted as GQD₂, GQD₆ and GQD₁₀ (increasing in size) were non-covalently attached to 2,9,16,23-tetrakis[4-(N-methylpyridyloxy)]-phthalocyanine (ZnTPPcQ) to form GQDs-ZnTPPcQ nanoconjugates. X-ray photoelectron spectroscopy (XPS) showed that increasing sizes of GQDs decreases the atomic concentrations of oxygen, which leads to blue shift in spectra of the GQDs. Relative to Pcs alone (0.03), the presence of GQDs improved the singlet oxygen quantum yields with the following values: GQD₂-ZnTPPcQ (0.17), GQD₆-ZnTPPcQ (0.27) and GQD₁₀-ZnTPPcQ (0.11). GQD₂-ZnTPPcQ nanoconjugate system had the most ZnTPPcQ loading, but did not generate the most singlet oxygen species due to aggregation. This study shows that, the quantity of oxygen, size and quality of GQDs as well as amount of Pc loading are amongst the vital properties to consider when constructing GQD-nanoconjugate systems with optimal singlet oxygen quantum yields.

A simple sonochemical approach to fabricate a urea biosensor based on zinc phthalocyanine/graphene oxide/urease bioelectrode

A novel zinc phthalocyanine/graphene oxide (ZnPh/GO) nanocomposite modified glassy carbon electrode (GCE) was prepared by using sonochemical approach and simple drop casting method. Urease (Urs) was used as the specific enzyme for urea detection and was physically immobilized onto the surface of ZnPh/GO nanocomposite. The fabricated ZnPh/GO/Urs matrix was successfully characterized by UV-vis-spectroscopy, FT-IR spectroscopy, scanning electron microscopy (SEM), raman spectrum, thermogravimetric analysis, cyclic voltammetric (CV) and amperometric techniques. The electrocatalytic performance of the ZnPh/GO/Urs electrode was investigated by urea biosensor. Our results demonstrate that the modified electrode has excellent electrocatalytic activity towards the sensing of urea in 0.1 M phosphate buffer solution (PBS, pH 7.2). The biosensor tolerated a wide linear concentration range for urea from 0.4 to 22 μM (R² = 0.991), with a detection limit of 0.034 µM (S/N = 3). The ZnPh/GO/Urs bioectrode has several excellent properties, including a fast response time, high reproducibility and stability.

Synthesis and photophysical properties of BODIPY-decorated graphene quantum dot–phthalocyanine conjugates

A BODIPY dye is linked to graphene quantum dots followed by immobilization of a Zn phthalocyanineviaπ–π stacking, resulting in improved triplet and singlet oxygen quantum yields.

Chemical functionalization and characterization of graphene-based materials

This review offers an overview on the chemical functionalization, characterization and applications of graphene-based materials.