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Two series with three Pt(II) complexes each (PtLPh‐n, PtLFpy‐n) bearing asymmetric tetradentate ligands as dianionic luminophores with variable alkyl chain lengths were synthesized. Hence, each ligand series is distinguished by one of its cyclometallating rings (phenyl vs. 2,6‐difluoropyrid‐3‐yl). Steady‐state and time‐resolved photoluminescence spectroscopic studies in diluted solutions at room temperature and in glassy matrices at 77 K show that the emissive state is mainly centered on the invariantly electron‐rich cyclometalated side while the second ring regulates the admixture of ligand‐centered and metal‐to‐ligand charge‐transfer character. Hence, the radiative rates can be controlled, as indicated by quantum‐mechanical calculations, which also explain the temperature‐dependent trend in the phosphorescence rate constants. Studies in condensed phases (single‐crystal X‐ray diffractometry, polarized optical microscopy, differential scanning calorimetry, steady‐state and time‐resolved photoluminescence micro(spectro)scopy) showed the development of a smectic A mesophase for the fluorinated species bearing the two longest alkyl chains. Nuclear magnetic resonance‐based studies on the thermodynamics of aggregation in solution confirm the marked enthalpic stabilization of aggregates mediated by the polar 2,6‐difluoropyrid‐3‐yl moiety (and to a lesser extent by dispersive forces between the alkyl chains). On the other hand, the negative entropy of aggregation is dominated by the restriction of degrees of freedom involving the peripheral alkyl moieties upon stacking, which becomes increasingly relevant for longer chains. All these factors control Pt···Pt coupling, a crucial interaction for the design of photofunctional mesogens based on Pt(II) complexes. [ABSTRACT FROM AUTHOR]

This work reports on a battery of coordination compounds featuring a versatile dianionic luminophore adopting three different coordination modes (mono, bi, and tridentate) while chelating Pd(II), Pt(II), Au(III), and Hg(II) centers. An in‐depth structural characterization of the ligand precursor (H2L) and six transition metal complexes ([HLPdCNtBu], [LPtCl], [LPtCNtBu], [LPtCNPhen], [HLHgCl], and [LAuCl]) is presented. The influence of the cations and coordination modes of the luminophore and co‐ligands on the photophysical properties (including photoluminescence quantum yields (ΦL), excited state lifetimes (τ), and average (non‐)radiative rate constants) are evaluated at various temperatures in different phases. Five complexes show interesting photophysical properties at room temperature (RT) in solution. Embedment in frozen glassy matrices at 77 K significantly boosts their luminescence by suppressing radiationless deactivation paths. Thus, the Pt(II)‐based compounds provide the highest efficiencies, with slight variations upon exchange of the ancillary ligand. In the case of [HLPdCNtBu], both ΦL and τ increase over 30‐fold as compared to RT. Furthermore, the Hg(II) complex achieves, for the first time in its class, a ΦL exceeding 60% and millisecond‐range lifetimes. This demonstrates that a judicious ligand design can pave the way toward versatile coordination compounds with tunable excited state properties. [ABSTRACT FROM AUTHOR]

Two different hybrid nanosystems are prepared by loading highly crystalline, monodisperse magnetite nanocubes (MNCs) with phosphorescent Pt(II) complexes (PtCxs). One involves the encapsulation of the hydrophobic PtCx1 within an amphiphilic comb polymer (MNC@poly(maleic anhydride‐alt‐1‐octadecene) [PMAO]–PtCx1), whereas the other involves the direct binding of the hydrophilic PtCx2 to the surface of the MNC mediated by a ligand‐exchange procedure (MNC@OH–PtCx2). Both systems are evaluated as potential candidates for multimodal imaging in magnetic resonance imaging (MRI) and photoluminescence lifetime imaging micro(spectro)scopy (PLIM). PLIM measurements on agarose phantoms demonstrate significantly longer excited‐state lifetimes compared to the short‐lived autofluorescence of biological background. Additionally, both nanosystems perform as effective MRI contrast agents (CAs): the r2* values are 3–4 times higher than for the commercial CA ferucarbotran. MNC@PMAO–PtCx1 particles also cause significant increases in r2. While the ligand exchange procedure efficiently anchors PtCxs to the MNC surface, the polymeric encapsulation ensures higher colloidal stability, contributing to differences in PLIM and MRI outcomes. In these results, the successful integration of two complementary noninvasive imaging modalities within a single nanosystem is confirmed, serving as the impetus for further investigation of such systems as advanced multimodal–multiscale imaging agents with dual orthogonal readouts. [ABSTRACT FROM AUTHOR]

In this contribution, we describe a library of nine different molecular asterisks, all based on aromatic thioethers. Here, the substitution patterns of the central core unit bearing two nitriles and the rotors featuring methoxy groups were permuted. In addition, the photophysical properties in the solid and aggregated state were investigated. X‐ray diffractometry confirmed the molecular structures. In this frame, the molecular packing in the crystal lattice of the two polymorphs of mNoM was extensively studied and a correlation between photoluminescence and secondary interactions was evaluated. In the solid state, all compounds showed emission in the yellow to red part of the electromagnetic spectrum (555–644 nm) with lifetimes of up to 25 μs and photoluminescence quantum yields of up to 47 %, depending on the substitution pattern. As all the evaluated compounds perform as good emitters with aggregation‐induced phosphorescence (AIP), these compounds can be regarded as multivalent platforms for future applications in supramolecular assemblies or as biomedical labels due to the versatile substitution patterns, manifold geometries as well as appealing photophysical properties. [ABSTRACT FROM AUTHOR]

In the frame of our research aiming to develop efficient triplet-emitting materials, we are exploring the concept of introducing additional heavy atoms into cyclometalated transition metal complexes to enhance intersystem-crossing (ISC) and thus triplet emission through increased spin–orbit coupling (SOC). In an in-depth proof-of-principle study we investigated the double cyclometalated Pt(II) complexes [Pt(C^N^C)(PnPh3)] (HC^N^CH = 2,6-diphenyl-pyridine (H2dpp) or dibenzoacridine (H2dba); Pn = pnictogen atoms P, As, Sb, or Bi) through a combined experimental and theoretical approach. The derivatives containing Pn = P, As, and Sb were synthesised and characterised comprehensively using single crystal X-ray diffraction (scXRD), UV-vis absorption and emission spectroscopy, transient absorption (TA) spectroscopy and cyclic voltammetry (CV). Across the series P < As < Sb, a red-shift is observed concerning absorption and emission maxima as well as optical and electrochemical HOMO–LUMO gaps. Increased photoluminescence quantum yields ΦL and radiative rates kr from mixed metal-to-ligand charge transfer (MLCT)/ligand centred (LC) triplet states are observed for the heavier homologues. Transient absorption spectroscopy showed processes in the ps range that were assigned to the population of the T1 state by ISC. The heavy PnPh3 ancillary ligands are found to enhance the emission efficiency due to both higher Pt–Pn bond strength and stronger SOC related to increased MLCT character of the excited states. The experimental findings are mirrored in hybrid (TD-)DFT calculations. This allowed for extrapolation to the rather elusive Bi derivatives, which were synthetically not accessible. This shortcoming is attributed to the transmetalation of phenyl groups from BiPh3 to Pt, as supported by experimental NMR/MS as well as DFT studies. [ABSTRACT FROM AUTHOR]

In the frame of our research aiming to develop efficient triplet-emitting materials, we are exploring the concept of introducing additional heavy atoms into cyclometalated transition metal complexes to enhance intersystem-crossing (ISC) and thus triplet emission through increased spin–orbit coupling (SOC). In an in-depth proof-of-principle study we investigated the double cyclometalated Pt(II) complexes [Pt(C^N^C)(PnPh3)] (HC^N^CH = 2,6-diphenyl-pyridine (H2dpp) or dibenzoacridine (H2dba); Pn = pnictogen atoms P, As, Sb, or Bi) through a combined experimental and theoretical approach. The derivatives containing Pn = P, As, and Sb were synthesised and characterised comprehensively using single crystal X-ray diffraction (scXRD), UV-vis absorption and emission spectroscopy, transient absorption (TA) spectroscopy and cyclic voltammetry (CV). Across the series P < As < Sb, a red-shift is observed concerning absorption and emission maxima as well as optical and electrochemical HOMO–LUMO gaps. Increased photoluminescence quantum yields ΦL and radiative rates kr from mixed metal-to-ligand charge transfer (MLCT)/ligand centred (LC) triplet states are observed for the heavier homologues. Transient absorption spectroscopy showed processes in the ps range that were assigned to the population of the T1 state by ISC. The heavy PnPh3 ancillary ligands are found to enhance the emission efficiency due to both higher Pt–Pn bond strength and stronger SOC related to increased MLCT character of the excited states. The experimental findings are mirrored in hybrid (TD-)DFT calculations. This allowed for extrapolation to the rather elusive Bi derivatives, which were synthetically not accessible. This shortcoming is attributed to the transmetalation of phenyl groups from BiPh3 to Pt, as supported by experimental NMR/MS as well as DFT studies. [ABSTRACT FROM AUTHOR]

In this work, we explored coordination compounds featuring caffeine‐based carbene co‐ligands and tridentate dianionic pincer luminophores derived from 2,6‐bis(1H‐1,2,4‐triazol‐5‐yl)pyridine (N), as well as from 2‐phenyl‐6‐(1H‐1,2,4‐triazol‐5‐yl)pyridine (C), bearing either Ad (adamantyl) or tBu (tertiary butyl) substituents. The new 2‐phenyl‐6‐(1H‐1,2,4‐triazol‐5‐yl)pyridine‐based ligand precursors along with four Pt(II) complexes, namely Pt(C‐tBu), Pt(C‐Ad), Pt(N‐tBu) and Pt(N‐Ad) were characterized. Further on, the influence of the different substituents at the chelating luminophores and of the caffeine‐based NHC‐co‐ligand on the photophysical properties (including photoluminescence quantum yields (ΦL), excited‐state lifetimes (τ), radiative (kr), and non‐radiative (knr) deactivation rate constants) was assessed in fluid solutions at room temperature (RT) and in frozen glassy matrices at 77 K. All four luminophores perform equivalently well within the experimental uncertainty. In deoxygenated fluid solutions at RT, photoluminescence quantum yields reaching up to 24 ± 2% and excited‐state lifetimes of around 12 μs were found. The generally long excited‐state lifetimes and only minor blue shift upon cooling to 77 K along with mostly well‐resolved vibrational progressions point to metal‐perturbed ligand‐centered excited states. Notably, the yield of the complexation reaction in case of Pt(C‐tBu) and Pt(C‐Ad) was almost two times higher compared to Pt(N‐tBu) and Pt(N‐Ad). Cyclometallation is not an essential feature to achieve high photoluminescence quantum yields, but it can improve the synthetic efficiency. In summary, it can be observed that coordination chemical concepts based on natural products can lead to stable phosphorescent species with interesting excited‐state properties. [ABSTRACT FROM AUTHOR]

The electrochemistry and photophysics of the Pt(II) complexes [Pt(naphen)(X)] (Hnaphen = naphtho[1,2-b][1,10]phenanthroline, X = Cl or C≡CPh) containing the rigid tridentate C^N^N-coordinating pericyclic naphen ligand was studied alongside the complexes of the tetrahydro-derivative [Pt(thnaphen)(X)] (Hthnaphen = 5,6,8,9-tetrahydro-naphtho[1,2-b][1,10]phenanthroline) and the N^C^N-coordinated complex [Pt(bdq)(Cl)] (Hbdq = benzo[1,2-h:5,4-h']diquinoline. The cyclic voltammetry showed reversible reductions for the C^N^N complexes, with markedly fewer negative potentials (around −1.6 V vs. ferrocene) for the complexes containing the naphen ligand compared with the thnaphen derivatives (around −1.9 V). With irreversible oxidations at around +0.3 V for all of the complexes, the naphen made a difference in the electrochemical gap of about 0.3 eV (1.9 vs. 2.2 eV) compared with thnaphen. The bdq complex was completely different, with an irreversible reduction at around −2 V caused by the N^C^N coordination pattern, which lacked a good electron acceptor such as the phenanthroline unit in the C^N^N ligand naphen. Long-wavelength UV-Vis absorption bands were found around 520 to 530 nm for the C^N^N complexes with the C≡CPh coligand and were red-shifted when compared with the Cl derivatives. The N^C^N-coordinated bdq complex was markedly blue-shifted (493 nm). The steady-state photoluminescence spectra showed poorly structured emission bands peaking at around 630 nm for the two naphen complexes and 570 nm for the thnaphen derivatives. The bdq complex showed a pronounced vibrational structure and an emission maximum at 586 nm. Assuming mixed 3LC/3MLCT excited states, the vibronic progression for the N^C^N bdq complex indicated a higher LC character than assumed for the C^N^N-coordinated naphen and thnaphen complexes. The blue-shift was a result of the different N^C^N vs. C^N^N coordination. The photoluminescence lifetimes and quantum yields ΦL massively increased from solutions at 298 K (0.06 to 0.24) to glassy frozen matrices at 77 K (0.80 to 0.95). The nanosecond time-resolved study on [Pt(naphen)(Cl)] showed a phosphorescence emission signal originating from the mixed 3LC/3MLCT with an emission lifetime of around 3 µs. [ABSTRACT FROM AUTHOR]

Supramolecular polymers (SPs) of d8 transition metal complexes have received considerable attention by virtue of their rich photophysical properties arising from metal‐metal interactions. However, thus far, the molecular design is restricted to complexes with chelating ligands due to their advantageous preorganization and strong ligand fields. Herein, we demonstrate unique pathway‐controllable metal‐metal‐interactions and remarkable 3MMLCT luminescence in SPs of a non‐chelated PtII complex. Under kinetic control, self‐complementary bisamide H‐bonding motifs induce a rapid self‐assembly into non‐emissive H‐type aggregates (1A). However, under thermodynamic conditions, a more efficient ligand coplanarization leads to superiorly stabilized SP 1B with extended Pt⋅⋅⋅Pt interactions and remarkably long 3MMLCT luminescence (τ77 K=0.26 ms). The metal‐metal interactions could be subsequently exploited to control the length of the emissive SPs using the seeded‐growth approach. [ABSTRACT FROM AUTHOR]

Supramolekulare Polymere (SPs) von d8‐Übergangsmetallkomplexen haben aufgrund ihrer vielseitigen photophysikalischen Eigenschaften, die sich u. a. aus Metall‐Metall‐Wechselwirkungen ergeben, an Bedeutung gewonnen. Bislang ist das molekulare Design jedoch auf Komplexe mit chelatisierenden Liganden beschränkt, aufgrund ihrer vorteilhaften Präorganisation und starken Ligandenfeldaufspaltungen. In diesem Manuskript berichten wir über einzigartige Metall‐Metall‐Wechselwirkungen und eine bemerkenswerte 3MMLCT‐Lumineszenz in SPs eines nicht chelatisierten PtII‐Komplexes, welche durch den Aggregationspfad kontrolliert werden können. Unter kinetischer Kontrolle induzieren selbstkomplementäre Bisamid‐H‐Bindungsmotive eine schnelle Selbstorganisation zu nicht‐emissiven H‐Aggregaten (1A). Unter thermodynamischen Bedingungen hingegen führt eine effizientere Liganden‐Koplanarisierung zu stärker stabilisierten SP 1B mit ausgedehnten Pt⋅⋅⋅Pt‐Wechselwirkungen und bemerkenswert langer 3MMLCT‐Lumineszenz (τ77 K=0.26 ms). Die Metall‐Metall‐Wechselwirkungen konnten anschließend genutzt werden, um die Länge der emittierenden SPs durch Keim‐vermitteltes SP‐Wachstum zu kontrollieren. [ABSTRACT FROM AUTHOR]