Tomasz Pedzinski

The germanium-grafted compound with a Donor–Bridge–Acceptor architecture, (E)-3-(dimethyl(4-vinylstyryl)germyl)-9-isopropyl-carbazole (1), was designed and synthesized as a potential blue-light emitter. Its previously reported silicon analogue (2) displays efficient blue-light emission resulting from photoinduced intramolecular electron transfer (ET) from carbazole to the divinylbenzene moiety through the dimethylsilyl bridge. In the current work, comparative photophysical studies combined with theoretical computations (DFT and NBO analysis) were aimed at understanding the role of the bridge atom in the photoinduced electron transfer as the source of blue emission. It was found that similarities of the bridge atoms (Ge and Si) translate into numerous similarities in the investigated organometallic compounds, endowing compounds 1 and 2 with unique properties and making them a good platform for complete electron transfer. By contrast, theoretical calculations of their carbon analogue (3) show that upon excitation only half of the electron charge can be transferred from the donor to the acceptor part. Despite many similarities, replacing silicon with germanium atom leads to a significant (about 10-fold) diminution of the ICT fluorescence quantum yield, resulting from the internal heavy-atom effect of germanium. Enhanced intersystem crossing of compound 1 (15-times larger spin-orbit coupling than that of compound 2) competes with electron transfer, making ET less efficient. Our findings show that the bridge atom controls excited-state dynamics via the modulation of competing deactivation pathways in the investigated systems.

Nitrile-appended Jäger-type N ₂ O ₂ ligands allow sensitive off–on fluorescence sensing of Mg( ii ) complex formation from challenging sources and qualify as chemically robust functional models of chlorophyll.

This communication aims to comprehensively elucidate the intricate mechanism governing the interaction between the excited triplet state of 4-Carboxybenzophenone (CB*) and the anionic form of 2-Naphthalene Sulfonate (NpSO₃⁻), employing the 337 nm Nanosecond Laser Flash Photolysis technique for this investigation. When the CB is selectively excited by a 337 nm laser, two primary processes become possible: (i) energy transfer from ³CB* to NpSO₃⁻ and (ii) electron transfer from NpSO₃⁻ to ³CB*. The dynamics of these interactions are explored through experimental observations of transient absorption spectra and the analysis of respective kinetic traces. The primary process dominating in the ³(CB...NpSO₃⁻)* system is identified as triplet energy transfer from excited ³CB* to ³(NpSO₃⁻), as demonstrated by characteristic spectral features observed at 410–420 nm. Comparisons are made with a similar system studied by Yamaji and co-workers, ³(BP^•−...NpO^•)*, revealing differences in the priority of primary process occurrences. These findings contribute to a deeper understanding of the intricate interactions between excited molecules and ground-state donors, aiding in the comprehension of mechanisms governing these reactions.

The effects of photochemical reactions induced by UV radiation in solutions of metal phthalocyanines were carried out to determine the factors that might influence the photostability of photosensitized phthalocyanines. Three different indium phthalocyanines, including the diindium triple-decker phthalocyanine, In₂Pc₃ (1), sandwich indium phthalocyanine, InPc₂ (2) and iodoindium phthalocyanine, InPcI (3) in benzene, N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), dichloromethane (DCM) and 1-chloronaphtalene, were studied. The rate of decay of absorption is explained by a decomposition reaction that is of first-order kinetics with respect to the phthalocyanine concentration. In general, the presence of ligand I⁻ in phthalocyanine InPcI enhances the rate of decomposition. The kinetics of the degradation process proved to depend on the molecular structure of the complex and seems to be controlled by interactions of the macrocycle bridging nitrogen atoms with the solvent molecules. The indium phthalocyanines in benzene displayed the capacity for singlet oxygen generation.

In the present study, we investigated the photooxidation of the biomimetic model of C-terminal methionine, N-Acetyl-Methionine (N-Ac-Met), sensitized by a 3-Carboxybenzophenone (3CB) excited triplet in neutral and basic aqueous solutions. The short-lived transient species that formed in the reaction were identified and quantified by laser flash photolysis and the final stable products were analyzed using liquid chromatography coupled with high-resolution mass spectrometry (LC-MS) and tandem mass spectrometry (MSMS). Based on these complementary methods, it was possible to calculate the quantum yields of both competing reactions, and the deprotonation was found to be favored over decarboxylation (for neutral pH: ϕ_-H = 0.23 vs. ϕ_-CO2 = 0.09, for basic pH: ϕ_-H = 0.23 vs. ϕ_-CO2 = 0.05). Findings on such a model system, which can possibly mimic the complex protein environment, are important in understanding complicated biological systems, for example, the studied compound, N-Ac-Met, can, to some extent, mimic the methionine in the C-terminal domain of β-amyloid, which is thought to be connected with the pathogenesis of Alzheimer’s disease.

This work presents the synthesis and characterization of metal-free, zinc (II), and cobalt (II) porphyrins substituted with short PEG chains. The synthesized compounds were characterized by UV-Vis, ¹H and ¹³C NMR spectroscopy, and MALDI-TOF mass spectrometry. The origin of the absorption bands for tested compounds in the UV-Vis range was determined using a computational model based on the electron density functional theory (DFT) and its time-dependent variant (TD-DFT). The photosensitizing activity was evaluated by measuring the ability to generate singlet oxygen (ΦΔ), which reached values up to 0.54. The photodynamic activity was tested using bladder (5637), prostate (LNCaP), and melanoma (A375) cancer cell lines. In vitro experiments clearly showed the structure–activity relationship regarding types of substituents, their positions in the phenyl ring, and the variety of central metal ions on the porphyrin core. Notably, the metal-free derivative 3 and its zinc derivative 6 exerted strong cytotoxic activity toward 5637 cells, with IC₅₀ values of 8 and 15 nM, respectively. None of the tested compounds induced a cytotoxic effect without irradiation. In conclusion, these results highlight the potential value of the tested compounds for PDT application.

Pt, Ru, and Ir were introduced onto the surface of graphitic carbon nitride (g-C₃N₄) using the wet impregnation method. A reduction of these photocatalysts with hydrogen causes several changes, such as a significant increase in the specific surface area, a C/N atomic ratio, a number of defects in the crystalline structure of g-C₃N₄, and the contribution of nitrogen bound to the amino and imino groups. According to the X-ray photoelectron spectroscopy results, a transition layer is formed at the g-C₃N₄/metal nanoparticle interphase, which contains metal at a positive degree of oxidation bonded to nitrogen. These structural changes significantly enhanced the photocatalytic activity in the production of hydrogen through the water-splitting reaction. The activity of the platinum photocatalyst was 24 times greater than that of pristine g-C₃N₄. Moreover, the enhanced activity was attributed to significantly better separation of photogenerated electron–hole pairs on metal nanoparticles and structural distortions of g-C₃N₄.

In the current work, comprehensive photophysical and electrochemical studies were performed for eight rhenium(I) complexes incorporating 2,2′:6′,2″-terpyridine (terpy) and 2,6-bis(pyrazin-2-yl)pyridine (dppy) with appended 1-naphthyl-, 2-naphthyl-, 9-phenanthrenyl, and 1-pyrenyl groups. Naphthyl and phenanthrenyl substituents marginally affected the energy of the MLCT absorption and emission bands, signaling a weak electronic coupling of the appended aryl group with the Re(I) center. The triplet MLCT state in these complexes is so low lying relative to the triplet ³IL_aryl that the thermal population of the triplet excited state delocalized on the organic chromophore is ineffective. The attachment of the electron-rich pyrenyl group resulted in a noticeable red shift and a significant increase in molar absorption coefficients of the lowest energy absorption of the resulting Re(I) complexes due to the contribution of intraligand charge-transfer (ILCT) transitions occurring from the pyrenyl substituent to the terpy/dppy core. At 77 K, the excited states of [ReCl(CO)₃(Lⁿ-κ²N)] with 1-pyrenyl-functionalized ligands were found to have predominant ³IL_pyrene/³ILCT_{pyrene→terpy} character. The ³IL/³ILCT nature of the lowest energy excited state of [ReCl(CO)₃(4′-(1-pyrenyl)-terpy-κ²N)] was also evidenced by nanosecond transient absorption and time-resolved emission spectroscopy. Enhanced room-temperature emission lifetimes of the complexes [ReCl(CO)₃(Lⁿ-κ²N)] with 1-pyrenyl-substituted ligands are indicative of the thermal activation between ³MLCT and ³IL/³ILCT excited states. Deactivation pathways occurring upon light excitation in [ReCl(CO)₃(4′-(1-naphthyl)-terpy-κ²N)] and [ReCl(CO)₃(4′-(1-pyrenyl)-terpy-κ²N)] were determined by femtosecond transient absorption studies.