Massive Stokes shift in 12-coordinate Ce(NO2)63-: crystal structure, vibrational and electronic spectra

Conjugated Molecular Nanotubes

Molecular compounds with permanent tubular architectures displaying radial π-conjugation are exceedingly rare. Their radial and axial delocalization presents them with unique optical and electronic properties, such as remarkable tuning of their Stokes shifts, and redox switching between global and local aromaticity. Although these tubular compounds display large internal void spaces, these attributes have not been extensively explored, thus presenting future opportunities in the development of materials. By using cutting-edge synthetic methodologies to bend aromatic surfaces, large opportunities in synthesis, property discovery, and applications are expected in new members of this family of conjugated molecular nanotubes.

Radially Oriented [n]Cyclo-meta-phenylenes

Molecular compounds with zigzag carbon nanotube geometries are exceedingly rare. Here we report the synthesis and characterization of carbon-based nanotubes with zigzag geometry, best described as radially oriented [n]cyclo-meta-phenylenes, extending the tubularene family of compounds. By the incorporation of edge-sharing benzene rings into the tubularene's radial π-surface, we have uncovered the first step to give rise to the emergence of radial orbital distribution in zigzag nanorings.

Zero-Overlap Fluorophores for Fluorescent Studies at Any Concentration

Fluorophores are powerful tools for the study of chemistry, biology, and physics. However, fluorescence is severely impaired when concentrations climb above 5 μM as a result of effects like self-absorption and chromatic shifts in the emitted light. Herein, we report the creation of a charge-transfer (CT) fluorophore and the discovery that its emission color seen at low concentrations is unchanged even at 5 mM, some 3 orders of magnitude beyond typical limits. The fluorophore is composed of a triphenylamine-substituted cyanostar macrocycle, and it exhibits a remarkable Stokes shift of 15 000 cm^-1 to generate emission at 633 nm. Crucial to the performance of this fluorophore is the observation that its emission spectrum shows near-zero overlap with the absorption band at 325 nm. We propose that reducing the spectral overlap to zero is a key to achieving full fluorescence across all concentrations. The triphenylamine donor and five cyanostilbene acceptor units of the macrocycle generate an emissive CT state. Unlike closely related donor-acceptor control compounds showing dual emission, the cyanostar framework inhibited emission from the second state to create a zero-overlap fluorophore. We demonstrated the use of emission spectroscopy for characterization of host-guest complexation at millimolar concentrations, which are typically the exclusive domain of NMR spectroscopy. The binding of the PF₆^- anion generates a 2:1 sandwich complex with blue-shifted emission. Distinct from twisted intramolecular charge-transfer (TICT) states, experiment-supported density functional theory shows a 67° twist inside an acceptor unit in the CT state instead of displaying a twist between the donor and acceptor; it is TICT-like. Inspired by the findings, we uncovered similar concentration-independent behavior from a control compound, strongly suggesting this behavior may be latent to other large Stokes-shift fluorophores. We discuss strategies capable of generating zero-overlap fluorophores to enable accurate fluorescence characterization of processes across all practical concentrations.