Antiaromatic macrocycles

How do macrocycles with [4n] electrons behave? Are there signatures of their formal antiaromaticity and how can their properties be tuned for practical applications? A recent study, led by Florian Glöcklhofer (Imperial College, London) endeavours to tackle these questions. A set of macrocycles based on []cyclophanetetraenes was synthesised, their redox and optical properties were measured, and a detailed computational analysis was performed.

Clear signatures of the unique properties of these macrocycles was found considering their large Stokes shifts (>1.5 eV) along with the ease of producing doubly charged states. A detailed computational analysis traces these properties back to the aromaticity of the excited and doubly charged states, respectively. In addition, it is illustrated how the properties of the macrocycles can be systematically varied with introduction of functional groups and variation of the aromatic units.

The study just appeared as a preprint on ChemRxiv: Functional Group Introduction and Aromatic Unit Variation in a Set of π-Conjugated Macrocycles: Revealing the Central Role of Local and Global Aromaticity.

Below, electron density difference plots for the charged states of the parent molecule paracyclophanetetraene are shown highlighting the cyclic symmetry of the electron attachment. The 2+/2- and 6+/6- states are aromatic whereas the 4+/4- singlet states are antiaromatic.

Photoredox catalysis

A study led by O. Koleoso and M. C. Kimber at Loughborough University explored a new route of synthesising conjugated N-acyliminium compounds. The article entitled “A complementary approach to conjugated N-acyliminium formation through photoredox-catalyzed intermolecular radical addition to allenamides and allencarbamates” just appeared in a thematic issue on Advances on photoredox catalysis in the Beilstein Journal of Organic Chemistry.

Solution processed solar cells

A study lead by J. Lowe and A. Malkov from Loughborough University investigates how kesterite solar cells can be formed via a new cheap and non-toxic solvent system. The associated paper just appeared in J. Mat. Chem. C: Solution processed CZTS solar cells using amine–thiol systems: understanding the dissolution process and device fabrication.

Quantum chemical computations were used to aid in the assignment of the structures produced and characterised via infrared multiple photon dissociation spectroscopy. An interactive model showing the relevant molecular vibrations can be found here.