Conformational Dynamics of Monomer- versus Dimer-like Features in a Naphthalenediimide-Based Conjugated Cyclophane

The design and synthesis of an enantiomeric pair of 1,8-diethynylanthracene-bridged naphthalenediimide (NDI)-based cyclophanes ( Cyclo-NDI s) are reported. Each enantiomer of Cyclo-NDI exhibits a circularly polarized luminescence signal with a relatively large luminescence dissymmetry factor (g_lum=±8×10⁻³). We have further investigated the modulation of through-space electronic communication between co-facially oriented NDIs in a discrete Cyclo-NDI with changes in the temperature. Tuning of the electronic communication results from the conformational transformation of monomer- versus dimer-like features of Cyclo-NDI , as confirmed by UV/Vis, fluorescence, circular dichroic, and NMR spectroscopic analysis. The temperature-dependent optical response in the Cyclo-NDI through the conformational transformation could be utilized as a highly sensitive and reversible optical thermometer in a wide temperature range (100 to −80 °C).     

Stimuli‐Responsive Dual‐Color Photon Upconversion: A Singlet‐to‐Triplet Absorption Sensitizer in a Soft Luminescent Cyclophane

Reversible emission color switching of triplet–triplet annihilation‐based photon upconversion (TTA‐UC) is achieved by employing an Os complex sensitizer with singlet‐to‐triplet (S‐T) absorption and an asymmetric luminescent cyclophane with switchable emission characteristics. The cyclophane contains the 9,10‐bis(phenylethynyl)anthracene unit as an emitter and can assemble into two different structures, a stable crystalline phase and a metastable supercooled nematic phase. The two structures exhibit green and yellow fluorescence, respectively, and can be accessed by distinct heating/cooling sequences. The hybridization of the cyclophane with the Os complex allows near‐infrared‐to‐visible TTA‐UC. The large anti‐Stokes shift is possible by the direct S‐T excitation, which dispenses with the use of a conventional sequence of singlet–singlet absorption and intersystem crossing. The TTA‐UC emission color is successfully switched between green and yellow by thermal stimulation.     

Crystallization‐Driven Asymmetric Helical Assembly of Conjugated Block Copolymers and the Aggregation Induced White‐light Emission and Circularly Polarized Luminescence

Controlling the self‐assembly morphology of π‐conjugated block copolymer is of great interesting. Herein, amphiphilic poly(3‐hexylthiophene)‐block‐poly(phenyl isocyanide)s (P3HT‐b‐PPI) copolymers composed of π‐conjugated P3HT and optically active helical PPI segments were readily prepared. Taking advantage of the crystallizable nature of P3HT and the chirality of the helical PPI segment, crystallization‐driven asymmetric self‐assembly (CDASA) of the block copolymers lead to the formation of single‐handed helical nanofibers with controlled length, narrow dispersity, and well‐defined helicity. During the self‐assembly process, the chirality of helical PPI was transferred to the supramolecular assemblies, giving the helical assemblies large optical activity. The single‐handed helical assemblies of the block copolymers exhibited interesting white‐light emission and circularly polarized luminescence (CPL). The handedness and dissymmetric factor of the induced CPL can be finely tuned through the variation on the helicity and length of the helical nanofibers.     

Detection of Circularly Polarized Luminescence of a Cs‐EuIII Complex in Raman Optical Activity Experiments

Circularly polarized luminescence (CPL) spectra are extremely sensitive to molecular structure. However, conventional CPL measurements are difficult and require expensive instrumentation. As an alternative, we explore CPL using Raman scattering and Raman optical activity (ROA) spectroscopy. The cesium tetrakis(3‐heptafluoro‐butylryl‐(+)‐camphorato) europium(III) complex was chosen as a model as it is known to exhibit very large CPL dissymmetry ratio. The fluorescent bands could be discriminated from true Raman signals by comparison of spectra acquired with different laser excitation wavelengths. Furthermore, the ROA technique enables fluorescence identification by measuring the degree of circularity. The CPL dissymmetry ratio was measured as the ROA circular intensity difference of 0.71, the largest one ever reported. The alternative CPL measurement enhances applications of lanthanides in analytical chemistry and chemical imaging of biological objects.     

Control of the Solid‐State Chiral Optical Properties of a Supramolecular Organic Fluorophore Containing 4‐(2‐Arylethynyl)‐Benzoic Acid

The solid‐state chiral optical properties of a 4‐(2‐arylethynyl)‐benzoic acid/amine supramolecular organic fluorophore can be controlled by changing the arylethynyl group of the achiral 4‐(2‐arylethynyl)‐benzoic acid component molecule rather than the chirality of the amine component molecule.     

Circularly Polarized Luminescence of Chiral Perylene Diimide Based Enantiomers Triggered by Supramolecular Self‐Assembly

Two perylene diimide (PDI) enantiomers ( d/l ‐PDI ) incorporating the d /l ‐alanine moiety have been designed and synthesized. d/l ‐PDI in chloroform displays bright‐yellow fluorescence that is redshifted to orange‐red when the solvent contains a methanol fraction of 99 vol %. No circular dichroism (CD) or circularly polarized luminescence (CPL) signals were observed for d/l ‐PDI enantiomers in CHCl₃. Interestingly, the d/l ‐PDI enantiomers exhibit clear mirror‐image Cotton effects and CPL emission in the aggregate state. The optical anisotropy factor (g_lum) is as high as 0.02 at f_m=99 %, which can be attributed to self‐assembly through intermolecular π–π interactions in the aggregate state.     

Circularly Polarized Luminescence of Chiral Pt(pppb)Cl (pppbH=1‐pyridyl‐3‐(4,5‐pinenopyridyl)benzene) Aggregate in the Excited State

We prepared enantiomers of chiral Pt^II complexes, Pt(pppb)Cl and Pt(pppb)CN (pppbH=1‐pyridyl‐3‐(4,5‐pinenopyridyl)benzene), and measured their CPL (circularly polarized luminescence) spectra for excimer and trimer emission. The contribution of the pinene moiety to CPL was considerably low for the π–π* emission of the monomer but large for MMLCT (metal‐metal‐to‐ligand charge‐transfer) of the excimer and trimer which had a helical structure induced in a face‐to‐face stacking fashion. The trimer CPL for (+)‐Pt(pppb)Cl was larger in intensity than that of excimer CPL; on the other hand, that for (+)‐Pt(pppb)CN was opposite in sign compared with that of excimer CPL. We conclude that differences in the excited‐state structure of the aggregate between Pt(pppb)Cl and Pt(pppb)CN account for the variation in the CPL spectra. By the aid of TD‐DFT calculations it was predicted that the dihedral angle θ(Cl‐Pt‐Pt‐Cl) was 50–60° or 110–140° for Pt(pppb)Cl aggregates and 160° for Pt(pppb)CN aggregates.     

Rhodium‐Catalyzed Highly Diastereo‐ and Enantioselective Synthesis of a Configurationally Stable S‐Shaped Double Helicene‐Like Molecule

An S‐shaped double helicene‐like molecule (>99 % ee), possessing stable helical chirality, has been synthesized by the rhodium(I)/difluorphos complex‐catalyzed highly diastereo‐ and enantioselective intramolecular double [2+2+2] cycloaddition of a 2‐naphthol‐ and benzene‐linked hexayne. The collision between two terminal naphthalene rings destabilizes the helical chirality of the S‐shaped double helicene‐like molecule, but the introduction of two additional fused benzene rings significantly increases the configurational stability. Thus, no epimerization and racemization were observed even at 100 °C. The enantiopure S‐shaped double helicene‐like molecule forms a trimer through the multiple C?H???π and C?H???O interactions in the solid‐state. The trimers stack to form columnar packing structures, in which neighboring stacks have opposite dipole directions. The accumulation of helical structures in the same direction in the S‐shaped double helicene‐like molecule enhanced the chiroptical properties.     

Assembly of the Thiolated [Au1Ag22(S‐Adm)12]3+ Superatom Complex into a Framework Material through Direct Linkage by SbF6− Anions

Building framework materials with desirable properties and enhanced functionalities with nanocluster/superatom complexes as building blocks remains a challenge in the field of nanomaterials. In this study, the chiral [Au₁Ag₂₂(S‐Adm)₁₂]³⁺ nanocluster/superatom complex (SC, in which S‐Adm=1‐adamantanethiol) was employed as a building block to construct the three‐dimensional (3D) superatom complex inorganic framework (SCIF) materials SCIF‐1 and SCIF‐2 through inorganic SbF₆^? linkers. SCIF‐1 is racemic due to the assembly of two SC enantiomers in a single crystal. In SCIF‐2, the SC enantiomers are packed in separate crystals, thus producing larger channels and a circularly polarized luminescence (CPL) response. These two 3D SCIF materials exhibit unique sensitive photoluminescence (PL) in protic solvents. Our study provides a new pathway for creating novel open‐framework materials with superatom complexes and a foundation for the further development of 3D framework materials for sensing and other applications.     

Structural Elucidation of Selective Solvatochromism in a Responsive‐at‐Metal Cyclometalated Platinum(II) Complex

We report the synthesis, characterization, and spectroscopic investigations of a new responsive‐at‐metal cyclometalated platinum(II) complex. With mild chemical oxidants and reductants, it was possible to obtain the same complex in three different oxidation states and each of these complexes was structurally characterized by single‐crystal X‐ray diffraction. We discovered that the platinum(II) complex displays strong solvatochromism in the solid state, which can be attributed to modulation of Pt???Pt interactions that results in switching between optical and photoluminescent states. Incorporating responsive‐at‐metal species as dynamic components in nanostructured materials might facilitate response amplification, sensing, actuation, or self‐healing processes.     

Model for Conformational Relaxation of Flexible Conjugated Polymers: Application to p‐Phenylenevinylene Trimers in Nonpolar Solvents

Photoexcitation of flexible conjugated polymers is invariably followed by a fast conformational/torsional relaxation towards a configuration favouring coplanarity of the conjugated segments. In general, the experimental relaxation rate constant (k_CR) depends on the solvent viscosity (η) and temperature (T), and is not proportional to T/η. A theory capable of explaining the observed dependence of k_CR on T and η over a wide range of these variables is not available. This gap is filled here by presenting a stochastic model that includes the participation of the oligomer side chain in storing and dissipating the stresses induced by photoexcitation. The model is able to account for the softening of solute–solvent interactions and its predictions are found to be in excellent agreement with the observed relaxation rate constants of a series of substituted p‐phenylenevinylene trimers [ChemPhysChem 2009 , 10, 448–454] on T, η and the size of the side‐chains.     

Preparation and Properties of New Soluble π‐Conjugated Polymers Containing a Fumaronitrile Unit in the Main Chain

Summary: A class of new, soluble, π‐conjugated polymers containing a fumaronitrile unit in the main chain were synthesized by the reaction between di(4‐bromophenyl)fumaronitrile and bis(2,2‐dimethylpropane‐1,3‐diyl)‐1,4‐dialkoxyphenylene‐2,5‐diborate employing palladium catalysts. All the polymers were photoluminescent and electrochemically active.

The new soluble π‐conjugated polymers 1a – d with photoluminescence and electrochemical activity synthesized here.     

Redox Multifunctionality in a Series of PtII Dithiolene Complexes of a Tetrathiafulvalene‐Based Diphosphine Ligand

The redox‐active and chelating diphosphine, 3,4‐dimethyl‐3′,4′‐bis(diphenylphosphino)‐tetrathiafulvalene, denoted as P2 , is engaged in a series of platinum complexes, [(P2)Pt(dithiolene)], with different dithiolate ligands, such as 1,2‐benzenedithiolate (bdt), 1,3‐dithiole‐2‐thione‐4,5‐dithiolate (dmit), and 5,6‐dihydro‐1,4‐dithiin‐2,3‐dithiolate (dddt). The complexes are structurally characterized by X‐ray diffraction, together with a model compound derived from bis(diphenylphosphino)ethane, namely, [(dppe)Pt(dddt)] . Four successive reversible electron‐transfer processes are found for the [(P2)Pt(dddt)] complex, associated with the two covalently linked but electronically uncoupled electrophores, that is, the TTF core and the platinum dithiolene moiety. The assignments of the different redox processes to either one or the other electrophore is made thanks to the electrochemical properties of the model compound [(dppe)Pt(dddt)] lacking the TTF redox core, and with the help of theoretical calculations (DFT) to understand the nature and energy of the frontier orbitals of the [(P2)Pt(dithiolene)] complexes in their different oxidation states. The first oxidation of the highly electron‐rich [(P2)Pt(dddt)] complex can be unambiguously assigned to the redox process affecting the Pt(dddt) moiety rather than the TTF core, a rare example in the coordination chemistry of tetrathiafulvalenes acting as ligands.     

Increasing the Open‐Circuit Voltage in High‐Performance Organic Photovoltaic Devices through Conformational Twisting of an Indacenodithiophene‐Based Conjugated Polymer

A fused ladder indacenodithiophene (IDT)‐based donor–acceptor (D–A)‐type alternating conjugated polymer, PIDTHT‐BT, presenting n‐hexylthiophene conjugated side chains is prepared. By extending the degree of intramolecular repulsion through the conjugated side chain moieties, an energy level for the highest occupied molecular orbital (HOMO) of –5.46 eV – a value approximately 0.27 eV lower than that of its counterpart PIDTDT‐BT – is obtained, subsequently providing a fabricated solar cell with a high open‐circuit voltage of approximately 0.947 V. The hole mobility (determined using the space charge‐limited current model) in a blend film containing 20 wt% PIDTHT‐BT) and 80 wt% [6,6]‐phenyl‐C₇₁ butyric acid methyl ester (PC₇₁BM) is 2.2 × 10^–9 m² V^–1 s^–1, which is within the range of reasonable values for applications in organic photovoltaics. The power conversion efficiency is 4.5% under simulated solar illumination (AM 1.5G, 100 mW cm^–2).