Our work has been accepted as cover art for Chemical Science. The figure shows an inositol phosphate binding to a lanthanide receptor molecule inducing a fluorescent respose.
The cover art illustrates the work Expedient synthesis and luminescence sensing of the inositol pyrophosphate cellular messenger 5-PP-InsP5 led by Stephen Butler at Loughborough and Barry Potter at Oxford.
We just posted a preprint discussing a question I have been wondering about for a while: Why is the lowest excited state of a molecule not always the HOMO/LUMO transition? More generally we show how singlet and triplet state energies are affected in different ways by post-MO energy terms.
The preprint can be found here: Excited-state energy component analysis for molecules – Why the lowest excited state is not always the HOMO-LUMO transition
Update: the final published version is available here.
A new book chapter by Patrick and Felix just appeared online: “Classification and Analysis of Molecular Excited States“. Ultimately, this chapter will be part of the Comprehensive Computational Chemistry series published by Elsevier.
In this chapter we explore the various ways in which excited states are classified, that is, according to
The map below shows the different classes and highlights the multitude of ways that are used to discuss excited states in the literature.
It is the purpose of this chapter to discuss all these types of states, covering the mathematical and physical background as well as the consequences to spectroscopy and photochemistry.
Our new paper “Classification of Doubly Excited Molecular Electronic States” just appeared in Chemical Science.
The topic of doubly excited states has been discussed quite controversially in the literature over the last couple of years, see for example JACS, 139, 13770 (2017) and JCTC 14, 9 (2018), and it is often disputed whether to classify a state as doubly excited at all. To contribute to this discussion we worked on the development of a physically motivated definition of doubly excited character based on operator expectation values and density matrices, which works independently of the underlying orbital representation. We hope that this approach will provide new understanding on these issues.
Kasha’s rule states that fluorescence generally occurs from the lowest excited singlet state (S1). Exceptions to this rule are usually associated with a metastable S2 state that is separated from S1 not allowing for interconversion. In a recent article we outlined a different mechanism for non-Kasha fluorescence: If S1 and S2 are very close in energy, then S2 is populated in a dynamic equilibrium following Boltzmann statistics. This effect is particularly pronounced if there is a large amount of vibrational excess energy following excitation into a high-energy absorption peak. The full story, “Non-Kasha fluorescence of pyrene emerges from a dynamic equilibrium between excited states” was just published in J. Chem. Phys.
Our new paper “Squarephaneic Tetraanhydride: A Conjugated Square-Shaped Cyclophane for the Synthesis of Porous Organic Materials” was just published in Angewandte Chemie. This paper, led by Florian Glöcklhofer from Imperial college, explores the redox chemistry, porosity, and chemical derivatives of a newly developed tetraanhyride based on a macrocycle with a formally antiaromatic ground state.
Our new paper “Hierarchical Assembly of a Micro-and Macroporous Hydrogen-Bonded Organic Framework with Tailored Single-Crystal Size,” led by Antonio Fernandez at Loughborough, just appeared in Angewandte Chemie.
The work shows how a highly porous framework can be constructed by using different types of intermolecular interactions.
Our new paper Using diketopyrrolopyrroles to stabilize double excitation and control internal conversion, led by Mariana do Casal and Mario Barbatti from Aix Marseille University, just appeared in PCCP. This work highlights how double excitation character can support internal conversion. Wavefunction analysis using TheoDORE sheds light into the wavefunctions involved.
Our new paper “Impact of Varying the Phenylboronic Acid Position in Macrocyclic Eu(III) Complexes on the Recognition of Adenosine Monophosphate“, led by S. E. Bodman and S. J. Butler from Loughborough, just appeared in Organic Chemistry Frontiers. The paper is the second in a series studying the anion sensing properties of Eu(III) complexes with phenylboronic acids.
Aside from reporting the synthesis and anion binding, the paper presents new strategies for the computational analysis of such complexes. Aside from modelling the geometries by density functional theory, high-level multireference methods in OpenMolcas were applied to study the luminescence properties. These first principles computations offer a promising approach to access the emission spectra of lanthanide complexes, aiding the design of responsive lanthanide probes with specific photophysical properties
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.