Anna Maroń

Colorectal cancer (CRC) remains a major global health burden, with approximately 2 million new cases and 1 million deaths annually. The growing resistance to conventional chemotherapy highlights the need for new therapeutic strategies against drug-resistant CRC. In this study, platinum(II) complexes of the general formula [PtCl(Ln)]CF3SO3, based on substituted 2,2′:6′,2″-terpyridines (Pt1) and 2,6-bis(thiazol-2-yl)pyridines (Pt2), were synthesized and evaluated for anticancer activity. Their antiproliferative effects were assessed in doxorubicin-sensitive and doxorubicin-resistant CRC cell lines, as well as primary dermal fibroblasts. Among the tested complexes, Pt1a showed the highest potency, exhibiting strong cytotoxicity against HCT116-DoxR cells (IC50 = 0.7 μM). Mechanistic studies revealed that Pt1a increases reactive oxygen species levels, binds DNA, disrupts cell cycle progression, and induces apoptosis and autophagy. Pt1a also displayed anti-metastatic and anti-angiogenic activities, showed favourable interaction with bovine serum albumin, and exhibited no detectable toxicity in a chicken embryo model.

Copper(II) complexes with 2,2′:6′,2″-terpyridines (terpys) are promising candidates for anticancer therapy and catalysis. Their structural and optical properties can be tuned by modifying the terpy backbone, including a substitution at the 4′ position or the replacement of peripheral pyridines with thiazole rings, forming 2,6-bis(thiazol-2-yl)pyridines (dtpys). dtpy-based copper(II) complexes (Cu-dtpys), despite their applicative potential, are barely characterized in the literature. Here, the series of Cu-dtpys (1–13) was synthesised and characterized by FT-IR, HRMS, X-ray diffraction, and UV-Vis spectroscopy. Their structural and optical features were compared to previously studied Cu-dtpys (14–24) and their terpy analogues (Cu-terpy-1 ÷ Cu-terpy-24). The detailed analysis revealed that five-coordinate Cu-dtpys complexes adopt a square pyramidal geometry comparable to that of Cu-terpys complexes but with markedly smaller deviations from the ideal square pyramid. Compared with Cu-terpys, Cu–Cl_apical bonds are shorter, while Cu–N_central bonds are elongated. The Cu-dtpy systems usually present the longest wavelength of the lowest energy absorption band in comparison to Cuterpys. The analysis of the relationship between Hammett’s constant and wavelength of absorption indicates that the most promising from the photophysical point of view are compounds 4–6, 10–13, 16–17, and 22, for which a newly formed intraligand charge transfer band is formed.

Controlling the spectral properties by changing external factors is a key ingredient in the search for new sensing materials. This work is focused on the photophysical response of [PtCl(tBuTPAterpy)] (where tBuTPAterpy = 4′-(4-(di(4-tert-butylphenyl)amino)phenyl)-2,2′,6′,2′′-terpyridine) (C). The examined compound was synthesized and characterized by acquiring UV-vis and photoluminescence (PL) spectra in solutions and in the solid state at room and low temperatures. Its photophysical properties were discussed in relation to those of [PtCl(4′-(CH₃)₂NPh-terpy)]CF₃SO₃ (A) and [PtCl(4′-Ph₂NPh-terpy)]CF₃SO₃ (B), which have a similar donor–acceptor structure, in order to emphasise the beneficial features of the studied compound. At room temperature, its photoluminescence is ‘ON’ in a viscous medium (triacetine), whereas in non-viscous media, no emission signal was observed. The rotation of the substituent may be the factor responsible for the lack of emission in dilute solutions. To support this hypothesis, a series of experiments was performed, which showed that the photoluminescence is switched on under conditions of low temperature, acid–base equilibrium, viscosity and aggregation. Compound C exhibits reversible mechanochromism with a colour change from red to brown and an emission shift from 708 nm to 783 nm. PXRD and SEM techniques were employed to support the observation of mechanochromic changes. The attractive solid-state photophysical properties, including reversible mechanochromism and tunable emission, indicate that compound C is a promising candidate for exploration for OLED applications.

The ‘wire-like’ acetylenic moiety is an important building block in organic and coordination chemistry that can facilitate electron transfer in donor–acceptor compounds, contributing to the enhancement of their photophysical properties. 2,6-Bis-(thiazol-2-yl)pyridine (dtpy) functionalized with a 4-phenylacetylene group (Ph-C≡C-dtpy) was, for the first time, used for the preparation of [ReCl(CO)₃(Ph-C≡C-dtpy)] and [Pt(Ph-C≡C-dtpy)Cl]CF₃SO₃ in order to understand the properties derived from the use of the acetylenic substituent. The coordination ability of Ph-C≡C-dtpy toward Pt(II) and Re(I) centers was determined. All the studied compounds were characterized using FT-IR, ¹H NMR, and ¹³C NMR spectroscopies, elemental analysis and, in the case of the free ligand and rhenium(I) complex, single-crystal X-ray analysis was also used. Their electrochemical, photophysical, and thermal properties were compared with the previously described similar systems. The photoluminescence spectra of Ph-C≡C-dtpy, [ReCl(CO)₃(Ph-C≡C-dtpy)] and [Pt(Ph-C≡C-dtpy)Cl]CF₃SO₃ were investigated in solution and in the solid state at 298 K and 77 K. The experimental results were supported by the DFT and TD-DFT calculations. As a result of the introduction of the -C≡C- moiety into the organic ligand skeleton, the Re(I) and Pt(II) complexes display room-temperature emission. In the case of [Pt(Ph-C≡C-dtpy)Cl]CF₃SO₃, photoluminescence lifetime in a microsecond regime was observed, whereas nanosecond lifetime for [ReCl(CO)₃(Ph-C≡C-dtpy)] in solution is comparable to lifetimes previously observed for rhenium(I) compounds with 4-substituted dtpys.

Cu(II) complexes with 2,2':6',2″-terpyridines (terpy) and 2,6-bis(thiazol-2-yl)pyridines (dtpy) with 1- or 2-naphtyl and methoxy-naphtyl were synthesized to elucidate the impact of the triimine core, naphtyl linking mode, and presence of methoxy groups on the antiproliferative activity of [CuCl₂(Lⁿ)]. Their antiproliferative effect was analyzed in ovarian (A2780) and colorectal (HCT116) carcinomas and colorectal carcinoma resistant to doxorubicin (HCT116-DoxR) cell lines and in normal human fibroblasts. Among all complexes, the 1- and 2-naphtyl substituted terpy Cu(II) complexes (Cu1a and Cu1b) showed the strongest cytotoxicity, namely, in HCT116-DoxR 2Dcells and were also capable of inducing the loss of cell viability in 3D HCT116-DoxR spheroids. Their intracellular localization, capability to increase reactive oxygen species (ROS), and interaction with DNA (nonintercalative mode) trigger oxidative DNA cleavage leading to cell death by apoptosis and autophagy. Cu1a and Cu1b do not show in vivo toxicity in a chicken embryo and can interact with bovine serum albumin (BSA).

A series of iridium(III) triimine complexes incorporating 2,2′:6′,2″-terpyridine (terpy) and 2,6-bis(thiazol-2-yl)pyridine (dtpy) derivatives were successfully designed and synthesized to investigate the impact of the peripheral rings (pyridine, thiazole) and substituents (thiophene, bithiophene, EDOT) attached to the triimine skeleton on their photophysical properties. The Ir(III) complexes were fully characterized using IR, ¹H, elemental analysis and single crystal X-ray analysis. Their thermal properties were evaluated using TGA measurements. Photoluminescence spectra of [IrCl₃L^1–6] were investigated in solution at 298 and 77 K. The experimental studies were accompanied by DFT/TDDFT calculations. The photophysical properties of the synthesized triimine ligands and Ir(III) complexes were studied in detail by electronic absorption and emission. In solution, they exhibited photoluminescence quantum yields ranging from 1.27% to 5.30% depending on the chemical structure. The experimental research included DFT/TDDFT calculations. The photophysical properties of the synthesized triimine ligands and Ir(III) complexes were conducted using electronic absorption and emission techniques. In solution, they displayed photoluminescence quantum yields ranging from 1.27% to 5.30% depending on the chemical structure.

This is the first comprehensive review of rhenium(I) carbonyl complexes with 2,2′:6′,2″-terpyridine-based ligands (R-terpy)—encompassing their synthesis, molecular features, photophysical behavior, and potential applications. Particular attention has been devoted to demonstrating how the coordination mode of 2,2′:6′,2″-terpyridine (terpy-κ²N and terpy-κ³N), structural modifications of terpy framework (R), and the nature of ancillary ligands (X—mono-negative anion, L—neutral ligand) may tune the photophysical behavior of Re(I) complexes [Re(X/L)(CO)₃(R-terpy-κ²N)]^0/+ and [Re(X/L)(CO)₂(R-terpy-κ³N)]^0/+. Our discussion also includes homo- and heteronuclear multicomponent systems with {Re(CO)₃(R-terpy-κ²N)} and {Re(CO)₂(R-terpy-κ³N)} motifs. The presented structure–property relationships are of high importance for controlling the photoinduced processes in these systems and making further progress in the development of more efficient Re-based luminophores, photosensitizers, and photocatalysts for modern technologies.

4′-(4-(di(4- tert -butylphenyl)amine)phenyl)-2,2′,6′,2′′-terpyridine presents a complex photodynamics tuned by the local environment, making it either an ‘early bird’ or a ‘night owl’.

The introduction of an electron-donating triphenylamine motive into a 2,2′,6′,2′′-terpyridine (terpy) moiety, a cornerstone molecular unit in coordination chemistry, opens new ways for a rational design of photophysical properties of organic and inorganic compounds. A push-pull compound, 4′-(4-(di(4-tert-butylphenyl)amine)phenyl)-2,2′,6′,2′′-terpyridine (tBuTPAterpy), was thoroughly investigated with the use of steady-state and time-resolved spectroscopies and Density Functional Theory (DFT) calculations. Our results demonstrate that solvent parameters have an enormous influence on the optical properties of this molecule, acting as knobs for external control of its photophysics. The Intramolecular Charge Transfer (ICT) process introduces a remarkable solvent polarity effect on the emission spectra without affecting the lowest absorption band, as confirmed by DFT simulations, including solvation effects. The calculations ascribe the lowest absorption transitions to two singlet ICT excited states, S₁ and S₂, with S₁ having several orders of magnitude higher oscillator strength than the “dark” S₂ state. Temperature and viscosity investigations suggest the existence of two emitting excited states with different structural conformations. The phosphorescence emission band observed at 77 K is assigned to a localized ³terpy state. Finally, protonation studies show that tBuTPAterpy undergoes a reversible process, making it a promising probe of the pH level in the context of acidity determination.