Author: Felix

Substituted macrocycles

Felix

A recent study, lead by Florian Glöcklhofer from Imperial College London, explores the effect of methoxy and thiomethyl subtitutions on a formally antiaromatic macrocycle. The corresponding paper “[2.2.2.2]Paracyclophanetetraenes (PCTs): cyclic structural analogues of poly(p‑phenylene vinylene)s (PPVs)” is available via Open Research Europe, 1, 111, 2012.

The above figure compares the orbitals and aromaticity descriptors for different charge and spin states. Importantly, the symmetry is broken in the T1 state, inhibiting Baird aromaticity. By comparison, the symmetry is retained for the neutral singlet, dianion, and dication states all of which exhibit aromaticity.

Reversible P-P bond cleavage

Felix

Recent work out of the group of Martin Smith at Loughborough University presents the possibility of cleaving a P-P bond at an iridium(III) metal centre by adding an AuCl unit.

Computations elucidate the underlying energetics and rationalise the results using the natural bond orbitals (NBO) approach.

Graphical abstract: Reversible P–P bond cleavage at an iridium(iii) metal centre

You can find the full text as an Advance Article in Chem. Commun.: Reversible P–P bond cleavage at an iridium(III) metal centre.

Luminescent lanthanide probes

Felix

Recent research led by Samantha Bodman and Steve Butler from Loughborough University presents a luminescent lanthanide probe with selective affinity for adenosine monophosphate (AMP), able to differentiate AMP from the more highly charged analogues ADP and ATP.

Density functional theory computations shed insight onto the binding modes involved.

You can find the full article at Chem. Sci. 2022, 13, 3386.

libwfa: Wavefunction analysis tools

Felix

Our new paper “libwfa: Wavefunction analysis tools for excited and open-shell electronic states” was just published in WiRES Comp. Mol. Sci. The libwfa library provides a variety of visual and qunantitative analysis tools to post-process excited-state computations performed within Q-Chem and OpenMolcas.

You can find the libwfa functionality in the Q-Chem documentation under General Excited-State Analysis. To activate libwfa in Q-Chem, use

state_analysis = true

In OpenMolcas use the WFA module, activated via

&WFA

Delayed fluorescence

Felix

Patrick’s first paper as first author just appeared in PCCP: The role of excited-state character, structural relaxation, and symmetry breaking in enabling delayed fluorescence activity in push-pull chromophores. Well done Patrick!

We were interested in understanding the difference in thermally activated delayed fluorescence (TADF) between two closely related donor-acceptor-donor systems using either an anthraquinone and benzodithiophenedione acceptor units, respectively. The first one was known to be an effective TADF emitter [JACS 2014, 136, 18070] whereas the second one had significantly lower quantum yield for TADF [PCCP 2019, 21, 10580].

Rather than just presenting energies, it was the purpose of this paper to shed detailed insight into the wavefunctions involved. Notable differences in the wavefunctions and charge-transfer character were found between the two molecules. Even more striking differences existed between different computational methods.

After evaluating electronic structure methods, we presented geometry optimisations in solution, highlighting the importance of symmetry breaking for producing an emissive lowest singlet state. The role of different solvation models was discussed as well.

Highly efficient photodynamics simulations

Felix

Molecules interacting with light undergo fascinating photodynamical processes inducing chemical reactions, transferring energy, or converting electronic energy into heat. These processes can be elucidated computationally via photodynamics simulations. However, these can be computationally highly demanding making the simulation of many interesting processes unfeasible.

A possible route to overcome this problem and to allow for efficient dynamics simulations is by combining vibronic coupling models (describing the energies) with the surface hopping method (describing the dynamics). We have introduced this idea two years ago [PCCP, 2019, 21, 57]. A new paper in Accounts of Chemical Research summarises developments since then: Surface Hopping Dynamics on Vibronic Coupling Models Acc. Chem. Res. 2021, 52, 3760.

Conjugated macrocycles

Felix

A recent study led by F. Glöcklhofer from Imperial College, London, investigates the properties of substituted conjugated macrocycles. The first (pre-review) version just appeared on Open Research Europe:

[2.2.2.2]Paracyclophanetetraenes (PCTs): cyclic structural analogues of poly(p‑phenylene vinylene)s (PPVs) by M. Pletzer, F. Plasser, M. Rimmele, M. Heeney, and F. Glöcklhofer.

Computations reveal the local and global aromaticity of the macrocycles in various electronic states by using the VIST method along with a discussion of the nodal structures of the orbitals.

Dominant natural difference orbitals (NDOs) (blue/red for electron detachment; green/orange for attachment) for different electronic states of O-PCT (C2 rotamer) and VIST plots for the S0 and T1 states at the S1 geometry. Copyright 2021 Pletzer M. et al. (CC-BY 4.0).