Competition between Singlet Fission and Spin-Orbit-Induced Intersystem Crossing in Anthanthrene and Anthanthrone Derivatives.

Singlet and triplet excited-state dynamics of anthanthrene and anthanthrone derivatives in solution are studied. Triisopropylsilyl- (TIPS) or H-terminated ethynyl groups are used to tune the singlet and triplet energies to enable their potential applications in singlet fission and triplet fusion processes. Time-resolved optical and electron paramagnetic resonance (EPR) spectroscopies are used to obtain a mechanistic understanding of triplet formation. The anthanthrene derivatives form triplet states efficiently at a rate (ca. 107  s-1 ) comparable to radiative singlet fluorescence processes with approximately 30 % triplet yields, despite their large S1 -T1 energy gap (>1 eV) and the lack of carbonyl groups. In contrast, anthanthrone has a higher triplet yield (50±10 %) with a faster intersystem crossing rate (2.7 × 108  s-1 ) because of the n-π* character of the S1 ←S0 transition. Analysis of time-resolved spin-polarized EPR spectra of these compounds reveals that the triplet states are primarily generated by the spin-orbit-induced intersystem crossing mechanism. However, at high concentrations, the EPR spectrum of the 4,6,10,14-tetrakis(TIPS-ethynyl)anthanthrene triplet state shows a significant contribution from a non-Boltzmann population of the ms =0 spin sublevel, which is characteristic of triplet formation by singlet fission.

Anthanthrene as a Super-Extended Tetraphenylethylene for Aggregation-Induced Emission.

Seven π-extended derivatives of the known tetraphenylethylene (TPE) have been studied for their aggregation-induced emission properties. Modulation of the emission properties of these anthanthrone-based luminogens has been accomplished through simple chemical modifications on four different positions of the anthanthrone core. The optical properties, along with X-ray diffraction and DFT-optimized structures, were studied. This work provides a new, easily accessible bridging unit for the TPE framework with a red-shifted emission.

Wurster-Type Anthanthrene Polyradicaloid Cations.

4,10-dibromoanthanthrone, a highly robust building block, is used to synthesize a bis(triarylamine) polymer. The polymer can be oxidized twice to form a polycationic macromolecule showing magnetic properties by electron paramagnetic resonance spectroscopy. In its dicationic state, the presence of isolated radicals is possible because of the interrupted conjugation between the diphenylamine with the anthanthrone core. The high steric hindrance prevents the planarity of the adjacent groups resulting in a polyradical cationic polymer. The oxidized polymer has a strong absorption in the near-infrared region along with reversible redox stages.

Wurster-Type Nanographenes as Stable Diradical Dications.

Three new and stable diradical dications based on the 4,10-dibromoanthanthrone have been synthesized and characterized. In their dicationic state, the amines show a biradical character in the ground state. Their magnetic properties have been investigated by NMR and EPR spectroscopies. The dicationic salts shows strong and broad optical absorption in the near-infrared region. The main driving force to obtain a ground state biradical is the high steric hindrance that prevents planarization of the diphenylamines with the anthanthrone aromatic core. The radical cations are isolated in two perpendicular π-systems as demonstrated by X-ray diffraction structures. This work provides a new bridging unit in the search for biradical bis(triarylamines) salts.

Breaking Bonds and Forming Nanographene Diradicals with Pressure.

New anthanthrone-based polycyclic scaffolds possessing peripheral crowded quinodimethanes have been prepared. While the compounds adopt a closed-shell butterfly-shaped structure in the ground state, a curved-to-planar fluxional inversion is accessible with a low energy barrier through a biradicaloid transition state. Inversion is primarily driven by the release of strain associated with steric hindrance at the peri position of the anthanthrone core; a low-lying diradical state is accessible through planarization of the core, which is attained in solution at moderate temperatures. The most significant aspect of this transformation is that planarization is also achieved by application of mild pressure in the solid state, wherein the diradical remains kinetically trapped. Complementary information from quantum chemistry, 1 H NMR, and Raman spectroscopies, together with magnetic experiments, is consistent with the formation of a nanographene-like structure that possesses radical centers localized at the exo-anthanthrone carbons bearing phenyl substituents.

Wireless Oxygen Sensors Enabled by Fe(II)-Polymer Wrapped Carbon Nanotubes.

Oxygen causes food spoilage and drug degradation, which is addressed commercially by modified atmosphere packaging. We report herein a wireless oxygen sensor, O2-p-CARD, from solution processed FeII-poly(4-vinylpyridine)-single-walled carbon nanotube composites on commercial passive near-field communication tags. A large irreversible attenuation in the reflection signal of an O2-p-CARD was observed in response to oxygen at relevant concentrations, enabling non-line-of-sight monitoring of modified atmosphere packaging. These devices allow for cumulative oxygen exposure inside a package to be read with a conventional smartphone. We have demonstrated that an O2-p-CARD can detect air ingress into a nitrogen-filled vegetable package at ambient conditions. This technology provides an inexpensive, heavy-metal-free, and smartphone-readable method for in situ non-line-of-sight quality monitoring of oxygen-sensitive packaged products.

Synthesis and Properties of Rhomboidal Macrocyclic Subunits of Graphdiyne-Like Nanoribbons.

Rhomboidal macrocyclic subunits of graphdiyne-like nanoribbon (GDNR) bearing both alkyne and diyne units, allowing for multichannel π-conjugation, were synthesized using an oxidative Glaser-type ring closing reaction. These subunits, called the "meshes" of the nanoribbon, possess phenyl groups with decyloxy solubilizing chains on each corner. The yields of the ring closing reaction highly depend on the metal (Cu or Pd) catalyst used for the macrocyclization step. Increasing the width of the meshes from one macrocycle to two fused macrocycles resulted in a decrease of the bandgap by 0.23 eV as shown by optical spectroscopy. The optimized geometries of the meshes alongside their HOMO and LUMO orbitals were calculated using DFT calculations at the B3LYP/6-31+G** level of theory. The results showed a nearly planar conformation for both meshes with HOMO and LUMO orbitals entirely delocalized over the molecules.

Rigid organic nanotubes obtained from phenylene-butadiynylene macrocycles.

Rigid organic nanotubes were prepared from six-membered phenylene-butadiynylene macrocycles through topochemical polymerization in the xerogel state. All six butadiyne units underwent polymerization, thus creating rigid nanotubes with six polydiacetylene chains lying parallel, one relative to each other.

Topochemical polymerization of phenylacetylene macrocycles: a new strategy for the preparation of organic nanorods.

Soluble organic nanorods were prepared from phenylacetylene macrocycles using the topochemical polymerization of butadiyne moieties placed both inside and outside the macrocycles' skeletons. Macrocycles containing amide groups were self-assembled in a columnar fashion through the formation of an organogel in ethyl acetate. Upon irradiation with UV light, the Raman signals associated with butadiyne units completely vanished, indicating the creation of covalently linked nanorods.