Achieving persistent room-temperature phosphorescence (RTP) in purely organic, heavy atom-free molecules is challenging due to intrinsically weak spin-orbit coupling and the occurrence of non-radiative decay. Here, we investigate a donor-acceptor naphthalonitrile derivative (NMe 2) that combines a pronounced charge-transfer (CT) character with a small singlet-triplet energy gap (Delta E ST), enabling efficient intersystem crossing (ISC), reverse intersystem crossing (RISC), and dual TADF/RTP emission. Comprehensive photophysical measurements reveal strong solvatochromism in solution and the emergence of temperature-dependent delayed emission in rigid matrices. In glassy 2Me-THF, polymethyl methacrylate (PMMA) films, and polymeric 3D-printed objects, NMe 2 exhibits long-lived phosphorescence with lifetimes in the millisecond-to-second range, facilitated by restricted molecular motion and reduced dioxygen quenching. Time-gated and transient photoluminescence studies suggest the coexistence of TADF and phosphorescence in PMMA, with phosphorescence dominating at low temperature. TDDFT calculations support the experimental observations, showing CT-dominated excited states, small Delta E ST values, and mixed singlet-triplet character that promotes efficient ISC. These results highlight the potential of simple donor-acceptor scaffolds as versatile emitters for the development of heavy-atom-free luminescent materials for advanced photonic and optoelectronic applications.

Photoresponsive molecular systems uniting light-controlled switching and luminescence are of great interest for next-generation optoelectronic materials. However, azoarenes in which both photoisomerization and emission are triggered and modulated under a single wavelength remain exceedingly rare. To address these challenges, arylazopyrazoles were combined with heteropentacene luminophores to yield fluorescent photoswitches. In-depth investigations were conducted to understand the concurrent photoluminescence and isomerization in solution, including temperature-dependent NMR studies, measurements of absolute photoluminescence quantum yields, and excited-state lifetimes. The findings were supported by quantum chemical calculations of the excited-state processes, which revealed the interplay between emissive and isomerization pathways, leading to a design concept for fluorescent photoswitches based on arylazopyrazoles. Finally, the application of these multi-responsive emitters was examined by embedding them into liquid crystalline and 3D-printed materials to investigate the effects of temperature, photoswitching, and order on photoluminescence - a pathway to next-generation photoresponsive materials.

Ratiometric optical sensors, which provide real-time measurements by comparing the intensities of two spectrally separated emission bands, are highly effective for monitoring oxygen levels. By combining oxygen-independent and oxygen-sensitive emission characteristics, they offer accurate quantification, distinguishing them from other sensor types. In this work, we designed a ratiometric optical sensor concept based on a bis-cyclometalated platinum(II) complex coupled with an organic naphthalonitrile-based fluorophore and incorporated it into mesoporous silica nanoparticles. This encapsulation strategy significantly improved the stability and water-dispersibility of the otherwise hydrophobic coordination compound while preventing aggregation and enhancing its photophysical properties. Both the free molecule and its nanoparticle-encapsulated form were characterized, revealing high sensitivity to oxygen variations with the unique feature of self-referenced ratiometric readout. The sensor's response was effectively measured at the single-particle level using photoluminescence microscopy, providing temporally and spatially resolved oxygen readouts. The versatility of the system was demonstrated across different experimental setups, including suspensions, solids, and agarose-embedded forms, highlighting its adaptability to a wide range of applications. This system holds significant promise for advanced oxygen monitoring, offering a reliable tool for high-resolution detection in complex environments with multiple orthogonal readouts.

An organometallic phosphorescent Pt II complex is introduced into DNA duplexes via oxidative addition to a tailor‐made artificial nucleobase, acting as an N^N^C donor ligand. Its covalent attachment to the nucleic acid backbone localizes the metal ion in the center of the duplex. The platination exerts a stabilizing effect of up to 6.4 °C on the duplex, with the degree of stabilization depending on the identity of the nucleobase in the complementary position. No interstrand crosslink is formed, as indicated by mass‐spectrometry and corroborated by almost identical photoluminescence lifetimes ( τ ) in Ar‐purged solution. In air‐equilibrated solution, τ shows moderate dependence on the complementary nucleobase, suggesting that the latter influences oxygen accessibility to the luminophore. When two Pt II complexes are incorporated in neighboring positions, a redshifted luminescence from aggregates is observed in addition to monomer emission, indicating Pt···Pt interactions along the helical axis. The approach presented here allows the site‐specific incorporation of highly stable Pt II complexes as phosphorescent tags into nucleic acids.

Accurate measurement of membrane potential dynamics is essential for understanding cellular excitability and signaling. While electrophysiological methods provide high temporal resolution, their invasiveness and low throughput limit their applicability in complex biological systems. Voltage-sensing dyes (VSDs) offer a powerful optical alternative, yet achieving near-infrared (NIR) emission, high sensitivity, and rapid response remains challenging. Here, we report the design, synthesis, and characterization of a novel phosphorus-rhodamine-based VSD (VSD 1) incorporating a phenyl substituent on the phosphorus atom. This modification enhances σ*–π* conjugation and electron-withdrawing effects, leading to a pronounced bathochromic shift with absorption and emission maxima at 715 and 744 nm, respectively—the most red-shifted spectral profile among reported rhodamine VSDs. VSD 1 shows strong fluorescence quenching in the resting state, suggesting efficient nonradiative deactivation, although the exact mechanism was not experimentally determined. Voltage-clamp fluorometry in Xenopus laevis oocytes demonstrates robust voltage sensitivity, with a linear fluorescence–voltage relationship and a ΔF/F of 4.7±1.4

Cycloplatinated complexes constitute an important class of luminescent compounds for sensing, bioimaging and optoelectronics. Their properties often depend on intermolecular non-covalent interactions between sterically unhindered square planar motifs. Here we investigated the photophysical behavior of novel platinum(ii)-rhenium(i) cyanido-/thiocyanato-bridged complexes [{Pt(C<^>N<^>N)}(& micro;-CN/SCN){Re(phen)(CO)3}]+ (-C<^>N<^>N = cyclometalated pincer ligand, phen = 1,10-phenanthroline) containing two chromophoric units. Their phosphorescence is dominated in solution by the platinum(ii) fragment derived from HC<^>N<^>N = phenylbipyridine, while major contribution of the rhenium(i) motif and dual emission are observed when HC<^>N<^>N = phenyl-pyrazolylpyridine and triazolyl-phenylpyridine ligand precursors are used. The solid-state behavior depends on intermolecular interactions between platinum components, the preferential mode of which is defined by the counterions. The complexes showcase a rare example of platinum(ii)-based bichromophoric compounds demonstrating vapo-/mechano-/thermo-induced reversible changes of optical properties and phase transformations, which could be interpreted as a result of switching between several conformations of noncovalently bound dimers.

In this work, we present a new class of cyclometalated Pt(II) complexes bearing tridentate luminophoric chelators. Inspired by picolinato units usually acting as ancillary ligands for phosphorescent Pt(II) and Ir(III) complexes with high-lying triplet states, we herein incorporate this coordination pattern into chelating luminophores toward tridentate pincer ligands (C^N^O) and compared them with a benzoate-derived motif (N^C^O). Both frameworks exhibit excellent photoluminescence efficiencies with quantum yields (ΦL) reaching up to 76% (N^C^O) and 75% (C^N^O). The versatile variation of the substitution patterns at the C^N^O motif was found to significantly affect the photophysical properties, yielding tunable emission maxima ranging from 475 to 693 nm. With the introduction of electron-donating substituents, it was demonstrated that an electron-rich cyclometalating ring at the luminophoric backbone enables the realization of Pd(II) complexes that are emissive in solution at room temperature, if combined with strong σ-donors (like N-heterocyclic carbenes) as co-ligands. This comparative study demonstrates that both coordination patterns yield highly efficient emitters with excellent solubilities in common organic solvents. Notably, the C^N^O-based motif offers distinct advantages for future applications, owing to its greater synthetic versatility and enhanced chemical accessibility.

We designed and synthesised an anionic small-molecular photosensitizer (aPSM-Cy3.5) for incorporation into electrostatic antibody targeted (ELART) vesicles, consisting of a protamine-coupled antibody as targeting unit, free protamine and aPSM-Cy3.5. These nanocarriers specifically internalize into different solid tumour cell lines. Upon illumination, the aPSM component initiates the production of reactive oxygen species (ROS). Tumour cells from lung, colorectal and pancreatic cancer with internalized aPSM show decreased growth in colony forming assay. This supports the development of systemically applicable anionic ROS inducers capable of specifically targeting tumour cells.

The synthesis, characterization, cyclovoltammetric and photophysical properties of 11 new d 8-configured Pt(II) complexes with N*N<^>C coordinated ligands, alternatively involving N*N six-ring and N<^>C five-ring chelates, are presented. By using various boronic acids, variation of the cyclometalating aryl units was achieved. The DFT-calculated HOMOs are localized on the metal with contributions from the Cl- coligand and either the phenyl/thiophenyl unit or the thiazolyl moiety, depending on the substitution pattern. The LUMOs have phenyl-pyridine pi*-character. Both calculated orbital sets agree well with the redox potentials from cyclic voltammetry. The TD-DFT calculated absorption spectra are in agreement with experimental data showing long-wavelength bands in the range from 400 to 500 nm, which matches the yellow color of the complexes. The ligand variation enabled a fine-tuning of the emissive properties related to the resulting complexes, going from greenish-blue (471 nm) to red (617 nm) phosphorescence. The position of the substituent affects the excited state properties, which is attributed to mesomeric and inductive effects on the Pt-C bond and the adjacent pyridine ring. In general, modulation of the excited state character can be achieved by variation of the cyclometalating unit, thus affecting the excited state energy as well as the radiative and radiationless deactivation rates.

Upregulation of K(Ca)3.1 channels was observed in highly aggressive tumor cells, such as non small cell lung cancer cells of the A549 line. In order to visualize K(Ca)3.1 channels in these cells, novel fluorescent probes with increased polarity were designed. Key step of the synthesis was a 1,3-dipolar cycloaddition of senicapoc propargyl ether 4 with various azide substituted bodipy dyes. Due to their reduced lipophilicity and promising photophysical properties, the senicapoc-bodipy conjugates 7a (logP = 4.3) and 16 (logP = 4.4) were able to stain K(Ca)3.1 ion channels in fixed, living, and permeabilized A549-3R tumor cells. The apparent size of the observed fluorescent dots indicates labeling of single K(Ca)3.1 channels. The recorded density is in good accordance with literature values. The specificity of K(Ca)3.1 labeling by the senicapoc-bodipy conjugates 7a and 16 was shown with HEK293 cells, blocking experiments and azide precursors. Subsequent staining of K(Ca)3.1 ion channels with hydroxyphenyl derivative 16 and antibodies did not lead to overlapping (yellow) dots, as different states of the ion channel were stained by 16 (open state) and antibody (closed state). In patch clamp experiments, both senicapoc-bodipy conjugates 7a and 16 reduced the current density, although less efficiently than senicapoc. MD simulations showed weaker interactions of the amide moiety of 16 with Thr250, explaining the lower channel inhibition of the open-pore blocker 16 compared to senicapoc (1). Due to their optimal imaging properties, high specificity, balanced lipophilicity/hydrophilicity, and sufficient water solubility, senicapoc-bodipy conjugates 7a and 16 represent innovative diagnostic tools to image K(Ca)3.1 channels.

In our research aimed at replacing precious transition metals like platinum with abundant base metals such as nickel for efficient triplet emitters, we synthesized and studied Ni(II) complexes [Ni(LNHR)Cl]. These complexes containing the N^C^N cyclometalating dipyridyl-phenide ligand, equipped with pending H-bonding amine groups (NH(C₆H₅) (LNHPh) and NH(C₆H₅CH₂), ClLNHBn). Molecular structures determined from experimental X-ray diffractometry and density functional theory (DFT) calculations in the ground state showed marked deviation of the Cl− coligand (ancillary ligand) from the ideal planar coordination, with τ4 values of 0.35 and 0.33, respectively, along with hydrogen bonding interactions of the ligand NH function with the Cl− coligand. The complexes exhibit long-wavelength absorption bands at approximately 425 nm in solution, with the experimental spectra being accurately reproduced through time-dependent density functional theory (TD-DFT) calculations. Vibrationally structured emission profiles and steady-state photoluminescence quantum yields of 30% for [Ni(LNHPh)Cl] and 40% for [Ni(LNHBn)Cl] (along with dual excited state lifetimes in the ns and in the ms range) were found in frozen 2-methyl-tetrahydrofuran (2MeTHF) glassy matrices at 77 K. Furthermore, within a poly(methyl methacrylate) matrix, the complexes showed emission bands centered at around 550 nm within a temperature range from 6 K to 300 K with lifetimes similar to 77 K. Based on TD-DFT potential scans along the metal–ligand (Ni–N) coordinate, we found that in a rigid environment that restricts the geometry to the Franck-Condon region, either the triplet T5 or the singlet S4 state could contribute to the photoluminescence.

In the frame of our research aiming to develop efficient triplet-emitting materials, we are exploring the role of the second coordination sphere in enhancing the rigidity of structures and its controlling aspect over the extents of excited state distortions. We thus synthesised three N^C^N cyclometalated complexes [M(LBn)Cl] (M = Pt, Pd, and Ni), where the two ortho-positions of the pyridyl moieties in 1,3-di(2-pyridyl)-benzene are benzyl substituted (Bn) forming a tight binding pocket for the metal and the Cl- ancillary ligand. The molecular structures from single-crystal X-ray diffraction show a markedly distorted square planar M(II) coordination with τ4 values of around 0.4. UV-vis absorption spectra show long-wavelength bands in the range 350 to 5400 nm with the energies increasing along the series Ni < Pt < Pd. The Pt(II) complex emits in solution at 298 K (λmax = 544 nm) and displays aggregated emission within poly(methyl methacrylate) (PMMA) films at various concentrations at 298 K. The Pd(II) derivative exhibits a broad emission band at 77 K in a frozen glassy 2-MeTHF matrix, peaking at 530 nm. Very different from the Pt(II) and Pd(II) spectra, the Ni(II) sample showed a broad emission with λmax = 699 nm at 77 K, with a quantum yield of 20% and ms lifetime. TD-DFT calculated decomposition of the assumed emissive T1 state showed similar 3MLCT character of about 30% for all three complexes, but marked differences in LC character of about 38% for Pd and Pt and only 5% for Ni. In turn, for Ni the by far the highest MC character (42%) was calculated which strongly speaks against triplet photoluminescence from the Ni(II) complex.

Background/Objectives: The Ca2+-activated K+ channel K(Ca)3.1 is not only involved in physiological processes such as immune reactions and control of vascular tone, but is highly expressed in various tumor entities. Thus, imaging of K(Ca)3.1 channels comes into focus for the localization of high channel density, i.e., for tumor diagnosis. In particular, the physicochemical properties of the fluorescent probes should be improved compared to existing probes. Methods: The small molecule inhibitor of the K(Ca)3.1 channel, senicapoc, was used as a warhead and was coupled with different fluorescent dyes. After synthesis of the novel probes, their physicochemical properties (lipophilicity, photophysical properties) and their ability to image K(Ca)3.1 channels in A549-3R lung tumor cells were determined. Results: In order to increase the polarity and quantum yield of reported fluorescent probes, three strategies were followed: (1) An F-atom at the B-atom of bodipy-labeled senicapoc derivatives 9a, 9b, and 15a was replaced by a OCH3 moiety, which decreased the logP value by one log-unit. (2) The p-phenylene moiety of the linker was replaced by an aliphatic tetramethylene linker decreasing the lipophilicity by 0.3-0.5 log-units. (3) Instead of bodipy dyes, fluorescein was coupled with the senicapoc warhead resulting in very polar probes 21a and 21b with low logP values of 1.5 and 1.3, respectively. Introduction of an ethyl moiety at the bodipy core increased the quantum yield, which resulted in the best punctate staining pattern of fixed and living A549-3R lung tumor cells with the ethylbodipy-labeled senicapoc derivative 10b. The specificity was shown by various control experiments. Co-staining with 10b and an antibody did not result in overlapping signals. Conclusions: The well-balanced lipophilicity and fluorescent quantum yield render the ethylbodipy-labeled senicapoc derivative 10b a very good probe to image selectively K(Ca)3.1 ion channels in fixed and living tumor cells. It was hypothesized that the antibody binds selectively at the closed channel (58.5%), whereas the senicapoc-bodipy conjugate 10b binds selectively at the open channel (41.5%). The ratio 58.5:41.5 reflects the ratio of the ion channel in closed and open conformations.

A family of coordination compounds with short intramolecular spatial separation between an organic chromophore and a metal center was studied. The specific geometry was realized by means of anthracene-functionalized tertiary aryl phosphanes. Their silver and gold complexes ( 1 , 2 ) operate as conventional fluorophores, with photophysical behavior defined by anthracene-localized allowed transitions. In contrast, bichromophoric species, containing phenyl bipyridine- ( 3 , 5 , 6 , 8 ) or terpyridine- ( 4 , 7 ) derived platinum(II) fragments, demonstrate fast intersystem crossing to the triplet state associated with the pincer metal component. Theoretical results corroborated that the short intramolecular distance between the platinum constituent and the adjacent anthracene facilitates subsequent through-space triplet ( T 2 , pincer fragment)→triplet ( T 1 , anthracene) energy transfer. This process occurs at a rate of ∼10 11 s −1 , surpassing the rates of T 2 →S 0 relaxation. This prevents visible phosphorescence from the platinum(II) motifs but enables near-IR organic phosphorescence in the solid state, including dyes with very inefficient intersystem-crossing (ISC). Thus, the composite molecules 3 – 8 illustrate a feasible approach to the tunable sensitization of organic dyes and the design of low-energy triplet emitters.

Square-planar d8-configured metal complexes and their excited states play a key role in photocatalysis, sensing, and optoelectronic devices. However, metal-to-ligand charge-transfer (MLCT) excited states involving transition metals, particularly those with a 3d8 electronic configuration, present challenges due to rapid nonradiative relaxation via low-lying metal-centered (MC) states. In this work, an isoelectronic and isostructural series of cyclometalated complexes [MX(dpb)] with M = Ni(II), Pd(II), and Pt(II), dpb = 1,3-di(2-pyridyl)phenide, and auxiliary ligand X = chlorido, azido, and triazolato were studied by UV/vis absorption, steady-state, and time-resolved photoluminescence spectroscopy in solution and frozen glassy matrix at 77 K, along with DFT calculations. Consistently, the Pd(II) and Pt(II) complexes exhibited a characteristic emission from their triplet ligand-centered (3LC) excited states. In contrast, Ni(II) complexes with auxiliary chlorido, azido, and triazolatoCOOCH3,COOCH3 ligands were nonemissive at low and room temperatures, due to the presence of low-lying MC-type ligand-field excited states. On the other hand, [Ni(triazolatoCoumarin,COOCH3)(dpb)] showed phosphorescence from the T5 state in a frozen glassy matrix at 77 K, since the restrictive environment limits structural relaxation, while at room temperature, the primary emission is due to singlet LC excited states from the coumarin moiety of the free ligand.

The control of self‐organized metal complexes presents advantages regarding the modulation of luminescence through dynamic assembly, rendering them promising for bioimaging. Herein, we demonstrate a strategy towards a series of amphiphilic Pt(II) complexes featuring bis‐cyclometalated ligands as tetradentate luminophores, which exhibit enhanced water solubility and tuneable self‐assembly properties. The resulting nanostructures can be precisely controlled by adjusting concentration and solvent composition, yielding switchable luminescence from red ( i. e ., excimer‐based) to green ( i. e ., monomer‐centred) and reversible (dis−)assembly of the aggregates. Cytotoxicity assays confirmed the innocuous nature of these luminophores at concentrations below 10 μM, while cellular uptake studies demonstrated effective internalization in both living and fixed cells. Using photoluminescence lifetime imaging micro(spectro)scopy, we determined that the complexes localized preferentially within lysosomes of living cells, while accumulating in the nuclei of fixed cells, with differences in photophysical behavior depending on whether the species were monomeric or excimeric in nature. These new findings provide insights into the systematic design of water‐soluble Pt(II)‐based luminophores with photophysical properties controlled by supramolecular interactions, underlining their potential for use in cellular imaging and diagnostics.

In an attempt to broaden the scope of functional nucleic acids, phosphorescent platinum(II) complexes, resembling artificial metal-containing nucleobases, were attached covalently to DNA oligonucleotides via a deoxyribose moiety. The distance between the deoxyribose and the complex was varied by selecting three different linkers (propylene, ethylene, and methylene). Stable duplexes were obtained with any of the canonical nucleobases in the complementary position. When guanine was placed in this position, the most stable duplexes were obtained. No clear correlation was found between the identity of the linker and duplex stability. When two platinum(II) complexes were placed in adjacent positions within an oligonucleotide strand, photoluminescence spectra exhibited an additional broad low-energy band due to luminescence with excimeric character, indicating Pt···Pt interactions. The ratio of monomeric and excimeric emissions depends on the linker length and, interestingly, on the presence of dioxygen. Hence, a platinated oligonucleotide was developed into a ratiometric dioxygen sensor, capable of rapidly detecting dioxygen levels in volumes as small as 2 μL. The oligonucleotide proved to be nontoxic at relevant concentrations and could be transfected into cells, where it appeared to degrade so that further modification will be necessary to obtain an oligonucleotide-based ratiometric dioxygen sensor for intracellular measurements.

In recent years, researchers studying fluorogenic samples have steadily shifted from using large, expensive, poorly soluble fluorophores with complex synthetic sequences to smaller, simpler π scaffolds with low molecular weight. This research article presents an in-depth study of the photophysical properties of five bridged single-benzene-based fluorophores (SBBFs) investigated for their solution and solid-state emission (SSSE) properties. The compounds O4, N1O3, N2O2, N3O1, and N4 are derived from a central terephthalonitrile core and vary in the amount of oxygen and nitrogen bridging atoms. These minimalized emitters show full-color tunable emission properties and exhibit moderate-to-high photoluminescence quantum yield values reaching up to 0.78 in dimethyl sulfoxide (DMSO). In addition to demonstrating excellent compatibility in poly(methyl methacrylate) (PMMA) films and additive manufacturing using stereolithography (SLA), white light emission was achieved in both solution and 3D-printed materials by controlling the mixing ratio of the compounds. Employing density-functional theory (DFT), well-correlating theoretical absorption and emission wavelengths were calculated as average values of the different possible conformers. Furthermore, cellular internalization of the substances was accomplished using Pluronic® F-127 nanoparticles. Overall, this study emphasizes the remarkable properties of single-benzene-based emitters, showcasing their accessibility and potential applications in biomedical fields and materials science.

Transition metal complexes are well-known for their efficient light emission and are promising for applications ranging from bioimaging to light-emitting diodes. In solution, interactions between the metal centers of two complexes become possible and drastically change the photophysical properties. For real-world devices, solid-state materials consisting of these molecules are preferable. Recently, the ligand-controlled aggregation of platinum(II) and palladium(II) complexes into molecular single crystals and the controlled formation of metal-metal contacts have been demonstrated. Here, we show how the metal-metal distance can be tuned in a controlled way by exerting pressure on the molecular crystal. Using optical spectroscopy inside a diamond anvil cell, we find strong and reversible piezochromism up to 18 GPa. Using time-dependent density functional theory, we attribute the wavelength shift to a reduction in the metal-metal distance and enhanced π orbital overlap in the dimers.