Ultrafast Exciton Self-Trapping and Delocalization in Cycloparaphenylenes: The Role of Excited-State Symmetry in Electron-Vibrational Coupling

Synthesis, Structures and Fluorescence Properties of gem-Linked Cyclic Tetraphenylethylenes and Cyclic hexaphenylethylenes

Rigid cyclic molecules are of great interest due to their intriguing structures and unique properties. Here, we report the facile synthesis of gem-linked cyclic tetraphenylethylenes and cyclic hexaphenylethylenes, namely [n]CTPEs...

Single-Molecule Magnet with Thermally Activated Delayed Fluorescence Based on a Metallofullerene Integrated by Dysprosium and Yttrium Ions

It is vital to construct luminescent single-molecule magnets (SMMs) and explore their applications in quantum computing technique and magneto-luminescence devices. In this work, we report a luminescent single-molecule magnet with thermally activated delayed fluorescence (TADF) based on metallofullerene DyY₂N@C₈₀. DyY₂N@C₈₀ was constructed by integrating dysprosium and yttrium ions into a fullerene cage. Magnetic results suggest that DyY₂N@C₈₀ exhibits magnetic hysteresis loops below 8 K originating from the Dy³⁺ ion. Moreover, DyY₂N@C₈₀ exhibits TADF originating from the Y³⁺-coordinated carbon cage, whose luminescence peak positions and peak intensities can be obviously influenced by Dy³⁺. Furthermore, a supramolecular complex of DyY₂N@C₈₀ and [12]Cycloparaphenylene ([12]CPP) was then prepared to construct a single-molecule magnet with multiwavelength luminescence. The effects of host-guest interaction on photoluminescence properties of DyY₂N@C₈₀ were disclosed. Theoretical calculations were also employed to illustrate the structures of DyY₂N@C₈₀ and DyY₂N@C₈₀⊂[12]CPP.

Naphthodithiophene Diimide Based Chiral π-Conjugated Nanopillar Molecules

The synthesis, structures, and properties of [4]cyclonaphthodithiophene diimides ([4]C-NDTIs) are described. NDTIs as important n-type building blocks were catenated in the α-positions of thiophene rings via an unusual electrochemical-oxidation-promoted macrocyclization route. The thiophene-thiophene junction in [4]C-NDTIs results in an ideal pillar shape. This interesting topology, along with appealing electronic and optical properties inherited from the NDTI units, endows the [4]C-NDTIs with both near-infrared (NIR) light absorptions, strong excitonic coupling, and tight encapsulation of C₆₀ . Stable orientations of the NDTI units in the nanopillars lead to stable inherent chirality, which enables detailed circular dichroism studies on the impact of isomeric structures on π-conjugation. Remarkably, the [4]C-NDTIs maintain the strong π-π stacking abilities of NDTI units and thus adopt two-dimensional (2D) lattice arrays at the molecular level. These nanopillar molecules have great potential to mimic natural photosynthetic systems for the development of multifunctional organic materials.

Triplet State Baird Aromaticity in Macrocycles: Scope, Limitations, and Complications

The aromaticity of cyclic 4nπ-electron molecules in their first ππ* triplet state (T1), labeled Baird aromaticity, has gained growing attention in the past decade. Here we explore computationally the limitations of T1 state Baird aromaticity in macrocyclic compounds, [n]CM's, which are cyclic oligomers of four different monocycles (M = p-phenylene (PP), 2,5-linked furan (FU), 1,4-linked cyclohexa-1,3-diene (CHD), and 1,4-linked cyclopentadiene (CPD)). We strive for conclusions that are general for various DFT functionals, although for macrocycles with up to 20 π-electrons in their main conjugation paths we find that for their T1 states single-point energies at both canonical UCCSD(T) and approximative DLPNO-UCCSD(T) levels are lowest when based on UB3LYP over UM06-2X and UCAM-B3LYP geometries. This finding is in contrast to what has earlier been observed for the electronic ground state of expanded porphyrins. Yet, irrespective of functional, macrocycles with 2,5-linked furans ([n]CFU's) retain Baird aromaticity until larger n than those composed of the other three monocycles. Also, when based on geometric, electronic and energetic aspects of aromaticity, a 3[n]CFU with a specific n is more strongly Baird-aromatic than the analogous 3[n]CPP while the magnetic indices tell the opposite. To construct large T1 state Baird-aromatic [n]CM's, the design should be such that the T1 state Baird aromaticity of the macrocyclic perimeter dominates over a situation with local closed-shell Hückel aromaticity of one or a few monocycles and semilocalized triplet diradical character. Monomers with lower Hückel aromaticity in S0 than benzene (e.g., furan) that do not impose steric congestion are preferred. Structural confinement imposed by, e.g., methylene bridges is also an approach to larger Baird-aromatic macrocycles. Finally, by using the Zilberg-Haas description of T1 state aromaticity, we reveal the analogy to the Hückel aromaticity of the corresponding closed-shell dications yet observe stronger Hückel aromaticity in the macrocyclic dications than Baird aromaticity in the T1 states of the neutral macrocycles.