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A series of phosphorus(V) porphyrins functionalized with meso-phenyl, tolyl, or 4-methoxyphenyl groups and axial-ethoxy, trifluoroethoxy, or ethylene glycoxy groups have been synthesized and their spectroscopic, redox, and optical properties were investigated. The X-ray crystal structures revealed a significant saddling in porphyrin molecular structures due to the presence of a small P(+5) ion in the cavity. The absorption and fluorescence properties are less sensitive to the meso-functionality, with small redshifts observed when moving from phenyl to tolyl and then to 4-methoxyphenyl on the phosphorus(V) porphyrin. In contrast, the meso- and axial-functionalities significantly influenced the redox properties. Specifically, the meso-4-methoxy phenyl group lowered the oxidation potentials, while the axial trifluoroethoxy units reduced the reduction potentials. This study demonstrates that by carefully choosing the axial and meso-substitutions, it is possible to selectively tune the redox potentials with minimal impact on optical properties. Steady-state and time-resolved measurements revealed relatively high fluorescence quantum yields, with lifetimes ranging from 2 to 4 ns. Together, the high fluorescence quantum yields and tunable redox potentials suggest that the investigated porphyrins could serve as excellent photosensitizers in model compounds for artificial photosynthesis and molecular electronic and photonic devices.

Nanobodies have been extensively demonstrated in biomedical imaging and therapy. However, nanobody probes often suffer from rapid renal clearance due to its small size. Herein, we reported a recombinant nanobody with a 200 amino-acid polypeptide chain consisting of Pro, Ala, and Ser (PAS) at the C-terminal, which can be easily expressed in Escherichia coli with a high yield. The PASylated nanobody was functionalized with a fluorescent dye and the cell labeling properties were characterized by flow cytometry and confocal microscopy. In vivo fluorescence imaging indicated that the PASylated nanobody showed comparable blood circulation time, but $\sim 1.5$ times higher tumor targeting ability as compared to the PEGylated nanobody of comparable molecular weight. Our findings demonstrate that nanobody PASylation is a promising approach to produce long-circulating nanobody probes for imaging and therapeutic applications.

$N$-methyl mesoporphyrin IX (NMM) is a water-soluble, non-symmetric porphyrin with excellent optical properties and unparalleled selectivity for G-quadruplex (GQ) DNA. G-quadruplexes are non-canonical DNA structures formed by guanine-rich sequences. They are implicated in genomic stability, longevity, and cancer. The ability of NMM to selectively recognize GQ structures makes it a valuable scaffold for designing novel GQ binders. In this review, we survey the literature describing the GQ-binding properties of NMM as well as its wide utility in chemistry and biology. We start with the discovery of the GQ-binding properties of NMM and the development of NMM-binding aptamers. We then discuss the optical properties of NMM, focusing on the light-switch effect — high fluorescence of NMM induced upon its binding to GQ DNA. Additionally, we examine the affinity and selectivity of NMM for GQs, as well as its ability to stabilize GQ structures and favor parallel GQ conformations. Furthermore, a portion of the review is dedicated to the applications of NMM-GQ complexes as biosensors for heavy metals, small molecules ($e.g.$ ATP and pesticides), DNA, and proteins. Finally and importantly, we discuss the utility of NMM as a probe to investigate the roles of GQs in biological processes.

A 10,20-bis(triisopropylsilylethynyl)tetrabenzo-5,15-diazaporphine (TIPS-TBDAP) was synthesized by the metal-template aza-annulation reaction. TIPS-TBDAP showed intense far-red fluorescence at 723 nm with a fluorescence quantum yield of 31% in chloroform solution. X-ray diffraction analysis revealed that TIPS-TBDAP forms a one-dimensional slipped $\pi$-stacking structure in the single crystal state. TIPS-TBDAP is soluble in common organic solvents owing to the bulky substituents and solution-processed field-effect transistors (FETs) could be fabricated. Dip-coating and single-crystal FETs showed the maximum hole mobilities of 1.5× 10${}^{-3}$ and 0.16 cm² V${}^{-1}$ s${}^{-1}$, respectively.

Investigation into the reactive oxygen species (ROS) generating abilities of photosensitizers outside of in-vitro/vivo conditions is a crucial element in the wider study of photodynamic therapy (PDT) in clinical settings. Zinc(II) phthalocyanine tetrasulfonic acid (ZnPcTS) is a water-soluble photosensitizer that can generate ROS as singlet oxygen (SO) under irradiation in the red and far-red region of the electromagnetic spectrum. The incorporation of ZnPcTS into nano-fibers of a bis-imidazolium hydrogel was demonstrated and the material was characterized with photophysical, rheological, and microscopy techniques. This supramolecular material containing ZnPcTS (named ZnPcTS_nEqBase@Gels) was found to significantly enhance the SO generation rate with respect to that of ZnPcTS in an aqueous solution. The effect is attributed mainly to reduced aggregation within the gel microenvironment compared with a solution. Furthermore, the preparation of ZnPcTS_nEqBase@Gels was carried out in the presence of varying amounts (0, 1, 2, 3, 4 eq.) of NaOH to improve the dissolution of ZnPcTSby ensuring full deprotonation of the sulfonate. The gel material containing 4 equivalents of NaOH per phthalocyanine was found to have a significantly greater SO-generating ability than the corresponding material containing no base. This phenomenon was shown to be partially a consequence of reduced aggregation as observed in the spectroscopic characterization. The enhancement in SO generation induced by this type of hybrid material makes it an attractive candidate to be used in different applications when efficient SO production is required.

Despite many notes about advantageous properties of Si(IV) phthalocyanines, their aza-analogues from the group of tetrapyrazinoporphyrazines (TPyzPzs) are only rarely reported in the literature, especially for macrocycles carrying peripheral groups. Thus, a series of Si(IV) TPyzPzs having alkylamino, aryloxy, alkylsulfanyl or alkyl group at the periphery was prepared by complexation of Si(IV) into corresponding metal-free derivatives by their stirring at 30${}^{\circ }$ C with trichlorosilane, using tributylamine as a base, and dichloromethane as a solvent. Key factors affecting the feasibility of this method, such as well-chosen excess of trichlorosilane and solvent used, were described. The model compound of the series ($i.e.$, aryloxy substituted dihydroxy Si(IV) TPyzPz) was then modified at axial positions using trihexylchlorosilane as a ligand. All target Si(IV) TPyzPzs showed strong absorption with Q-band maxima ranging 617–655 nm (extinction coefficients 82 000–341 000 L⋅mol${}^{-1}$⋅cm${}^{-1})$ and efficient fluorescence emission with ${\mathrm{\Phi }}_F$ values ranging 0.32–0.44 with the exception of alkylamino substituted TPyzPz, whose excited states were efficiently quenched by intramolecular charge transfer. The possibility of axial modification, good spectral and fluorescence properties as well as the ability to quench the excited states upon introduction of alkylamine groups indicate the suitability of these derivatives for fluorescence sensing applications.

A hitherto unknown butadiyne-linked BODIPY dimer (4) has been synthesized under the conventional Glaser coupling reaction conditions using the ethynyl-substituted pyrrolyl-BODIPY (2) prepared by gold-catalyzed C-H alkynylation. Due to the $\pi$-extended structure of the BODIPY chromophore in 4, a characteristic broad absorption band in the near-infrared (NIR) region has emerged. Upon photoexcitation, the environment-dependent fluorescence spectral features were observed. The fluorescent response varied with solvents, viscosity, and temperature, which was found to originate from the conformational changes between the coplanar and twisted conformers in the otherwise rigid butadiyne-bridged dimer 4. Therefore, the BODIPY dimer 4 would be a potential NIR fluorescence material for use in the probes responding to the distinct viscous environment in biological tissues.

The aggregative state of the Zn(II) tetra-spermine porphyrin derivative, ZnTCPPSpm4, has been investigated in the presence of different buffers at the same pH value: 5K (cacodylate) buffer, phosphate sodium salt buffer, and PBS. The photophysical characterizations (UV-vis, Fluorescence, and RLS) have indicated a precise self-assembly phenomenon depending on the buffered solution used. The porphyrin does not undergo a significant aggregation in 5K buffer, differently from what occurs in phosphate and PBS buffers. Here, the likely specific interaction between the phosphate molecules and spermine pendants leads to spontaneous porphyrin aggregation, as detected by the high fluorescence quenching, enhancement of the RLS signal, and a significant splitting of the porphyrin Soret band. As a result, the current paper aims to highlight the importance of the employed buffer throughout the experimental procedures performed in the presence of porphyrinoids.

During the pandemic period, we were forced to reconsider teaching of practical labs, as students had mainly to work at home. It was the occasion to explore the use of cheap microcontroller kits for teaching chemistry and to work out some manipulations with household products. Back to normal life, it is important to valorize this equipment and work to design simple chemistry experiments which could be performed by students at home with Arduino kits adapted to chemistry, to illustrate various courses in addition to classical manipulations performed in the laboratory with specific equipment and products. We describe here the construction of a simple and cheap Arduino-based fluorimeter and its use to study relative porphyrinoids (mainly chlorophylls and pheophytins) contents in olive oils, and the effect of heating on the degradation of such substances. We used an Arduino Uno kit with a LED, a light-to-frequency converter associated with an excitation-blocking filter, and a 3D-printed sample holder.

Expansion of porphyrin-like macrocycles can provide insights into the relationship between structural, optical, and electronic features. Here, we report the synthesis of a new nominally antiaromatic expanded porphyrin-like macrocycle (6) prepared via the condensation of 1,4-bis-(3,4-diethyl-2-pyrryl)benzene dialdehyde (4) with hydrazine. The absorption and emission features of this new macrocycle were compared to those of the parent bipyrrole-derived macrocycle, a system first reported in 1997. Attempts to oxidize both macrocycles (5 and 6) were unsuccessful, a failure ascribed to the steric limitations imposed by two substituents present on the $\beta$-positions on the di-substituted pyrrolic precursor. This stands in contrast to what was observed for the original bipyrrole system bearing only a single $\beta$-substituent on each of the pyrrolic moieties. The present results underscore the possible role of structure in governing electronic transitions in expanded porphyrins while highlighting the facility of hydrazine-based condensations in accessing readily large pyrrolic macrocycles.

Singlet–singlet and triplet-triplet energy-transfer processes between anthracenes and porphyrins have received considerable attention in materials chemistry. Herein, we report the first examples of 3,5-bis(10-phenylanthracen-9-yl)benzene-appended porphyrins (BPABPs) designed to study intramolecular energy transfer between two chromophores. The Curtius rearrangement of 3,5-bis(10-phenylanthracen-9-yl)benzoyl azide in the presence of the platinum(II) complex of 5,10,15-tris(3,5-di-tert-butylphenyl)-20-(3-hydroxyphenyl)porphyrin or its free base in toluene afforded the corresponding BPABP. Spectroscopy, cyclic voltammetry, and density functional theory calculations revealed that the anthracene and porphyrin $\pi$-electron systems of the BPABPs are not conjugated and consequently do not affect each other’s absorption properties. In contrast, the BPABPs exhibited considerably different luminescence properties to those of phenyl 3,5-bis(10-phenylanthracen-9-yl)carbamate and 5,10,15-tris(3,5-di-tert-butylphenyl)-20-(3-methoxyphenyl)porphyrins; the anthracene units of the BPABPs show considerably quenched fluorescence compared to that of the reference anthracene, indicative of efficient intramolecular singlet–singlet energy transfer from the anthracene to the porphyrin unit. The phosphorescence quantum yield of the Pt complex of BPABP is comparable to that of the reference Pt-porphyrin, which suggests that intramolecular triplet-triplet energy transfer from the Pt-porphyrin to the anthracene unit is inefficient. The present findings improve our understanding of how structural factors and excited-state energy levels affect energy transfer and triplet-triplet annihilation upconversion processes of covalently linked bisanthracene-appended porphyrins.

9-aminoporphycenes degrade over time, yielding products that emit in a similar spectral region as the parent compounds. This leads to a triple fluorescence pattern, with relative intensities changing with time, solvent, excitation wavelength, and irradiation. The decomposition products were analyzed using chromatography coupled with mass spectrometry, absorption, and emission measurements. The spectra of possible products were also calculated using density functional theory. We conclude that the degradation processes involve oxygenation that occurs both in the ground electronic state and as a photoinduced process, the latter being more efficient.

Zinc 3-hydroxymethyl-pyropheophorbides-$a$ covalently linked with an 8-aryl-1,3,5,7-tetramethyl-BODIPY moiety in the 17-substituent were synthesized by chemically modifying naturally occurring chlorophyll(Chl)-$a$. The synthetic Chl–BODIPY conjugates in tetrahydrofuran exhibited sharp visible absorption and weak circular dichroism spectra, indicating that their molecules were fully dispersed in the solution. In their ground states, no intramolecular interaction between the Chl and BODIPY parts was observed. By contrast, singlet excitation energy was efficiently transferred from the photoexcited BODIPY moiety to zinc chlorin moiety within their molecules. The intramolecular energy transfer efficiencies exceeded 90% and were independent of the linkages including ester and amide bonds as well as methylene and hexamethylene spacers.

A diaxial complex of the Sn(IV)-5,10,15,20-tetra-(4-carboxyphenyl)porphyrin with a fluorescein halogen derivative– Erythrosine B (triad “luminophore-porphyrinate-luminophore”) was synthesized. Its structure was established using NMR spectroscopy and mass spectrometry. Its luminescent properties (fluorescence spectra, quantum yield and fluorescence lifetime, as well as the ability to generate singlet oxygen) were studied. It has been established that the resulting triad has the properties of a fluorescent molecular rotor, and both fragments of the triad [porphyrinate (${\lambda }_{\text{ex}}$ = 420 nm) and xanthene (${\lambda }_{\text{ex}}$ = 470 nm) fragments] show high fluorescent sensitivity to local viscosity. By immobilizing the triad “luminophore-porphyrinate-luminophore” into a polymer matrix of polyvinyl alcohol (PVA), hybrid film materials were obtained. It has been shown that the fixation of the triad in the polymer matrix due to the formation of hydrogen bonds between carboxyl groups and the organic polymer does not have a significant effect on its luminescent properties. It has been established that both fragments in the triad immobilized in PVA-based polymer organic films retain their properties as fluorescent “molecular rotors” in non-aqueous media.

Peripheral phenyl-substituted metal phthalocyanines with thio and oxa substitution in the spacer bridge fragment were obtained in the work. Spectroscopic properties were studied for the obtained complexes, and the main patterns of behavior and characteristics change depending on the solvent and the nature of the spacer atom. It is shown that the replacement of an oxygen atom in the bridge fragment of a peripheral substituent with a sulfur atom leads to a change in the values of the fluorescence quantum yields. It was revealed that the presence of a spacer fragment is one of the key factors that strongly influence both the solubility of phthalocyanine complexes and their aggregation behavior in various solvents.

Multiphoton microscopy (MPM), with the advantages of improved penetration depth, decreased photo-damage, and optical sectioning capability, has become an indispensable tool for biomedical imaging. The combination of multiphoton fluorescence (MF) and second-harmonic generation (SHG) microscopy is particularly effective in imaging tissue structures of the ocular surface. This work is intended to be a review of advances that MPM has made in ophthalmic imaging. The MPM not only can be used for the label-free imaging of ocular structures, it can also be applied for investigating the morphological alterations in corneal pathologies, such as keratoconus, infected keratitis, and corneal scar. Furthermore, the corneal wound healing process after refractive surgical procedures such as conductive keratoplasty (CK) can also be studied with MPM. Finally, qualitative and quantitative SHG microscopy is effective for characterizing corneal thermal denaturation. With additional development, multiphoton imaging has the potential to be developed into an effective imaging technique for in vivo studies and clinical diagnosis in ophthalmology.

To provide a computational efficient forward model with moderate accuracy for rapid 3D optical tomography in small volumes, radiative transport in the delta-P1 approximation combined with the approximation of the reciprocity was examined. Perturbations of optical signals caused by absorption and fluorescence heterogeneities submerged in a resin-based liquid phantom with background parameters close to rat brain tissues were measured using a recently constructed laminar optical tomography system. These measured perturbations were used to examine the theoretically calculated fluence perturbations based on the delta-P1 approximation and the reciprocity approximation. Results show that the errors between the predicted and measured data are acceptable, especially for fluorescence perturbations.

There is a growing realization that cell-to-cell variations in gene expression have important biological consequences underlying phenotype diversity and cell fate. Although analytical tools for measuring gene expression, such as DNA microarrays, reverse-transcriptase PCR and in situ hybridization have been widely utilized to discover the role of genetic variations in governing cellular behavior, these methods are performed in cell lysates and/or on fixed cells, and therefore lack the ability to provide comprehensive spatial-dynamic information on gene expression. This has invoked the recent development of molecular imaging strategies capable of illuminating the distribution and dynamics of RNA molecules in living cells. In this review, we describe a class of molecular imaging probes known as molecular beacons (MBs), which have increasingly become the probe of choice for imaging RNA in living cells. In addition, we present the major challenges that can limit the ability of MBs to provide accurate measurements of RNA, and discuss efforts that have been made to overcome these challenges. It is envisioned that with continued refinement of the MB design, MBs will eventually become an indispensable tool for analyzing gene expression in biology and medicine.

We have imaged mitochondrial oxidation–reduction states by taking a ratio of mitochondrial fluorophores: NADH (reduced nicotinamide adenine dinucleotide) to Fp (oxidized flavoprotein). Although NADH has been investigated for tissue metabolic state in cancer and in oxygen deprived tissues, it alone is not an adequate measure of mitochondrial metabolic state since the NADH signal is altered by dependence on the number of mitochondria and by blood absorption. The redox ratio, NADH/(Fp + NADH), gives a more accurate measure of steady-state tissue metabolism since it is less dependent on mitochondrial number and it compensates effectively for hemodynamic changes. This ratio provides important diagnostic information in living tissues. In this study, the emitted fluorescence of mouse colon in situ is passed through an emission filter wheel and imaged on a CCD camera. Redox ratio images of the healthy and hypoxic mouse intestines clearly showed significant differences. Furthermore, the corrected redox ratio indicated an increase from an average value of 0.51 ± 0.10 in the healthy state to 0.92 ± 0.03 in dead tissue due to severe ischemia (N = 5). We show that the CCD imaging system is capable of displaying the metabolic differences in normal and ischemic tissues as well as quantifying the redox ratio in vivo as a marker of these changes.

Electrical stimulation of the mammalian neurohypophysial infundibular stalk evokes the entry of Na⁺ and Ca²⁺ into the neurosecretory terminals during the action potential. These events, in turn, increase intracellular Ca²⁺ and activate NaK- and Ca-ATPases, prompting the mitochondria to increase oxidative phosphorylation which can be monitored by recording the changes in FAD and NADH fluorescence. This paper reflects our efforts to determine whether or not modulating the capacity of mitochondria to produce ATP, by changing the concentrations of two important substrates of the Krebs cycle of the nerve terminal mitochondria, pyruvate and glucose, has an effect on the intrinsic fluorescence changes triggered by action potential stimulation.