Issue 11, 2020

Toward an understanding of electronic excitation energies beyond the molecular orbital picture

Abstract

Tuning the energies of molecular excited states is a central research theme in modern chemistry with high relevance for optoelectronic applications and chemical synthesis. Whereas frontier orbitals have proven to be an intuitive and simple model in many cases, they can only provide a very rough approximation of the underlying wavefunctions. The purpose of this Perspective is to explore how our qualitative understanding of electronic excitation processes can be promoted beyond the molecular orbital picture by exploiting methods and insights from modern quantum chemistry. For this purpose, the physics of a correlated electron–hole pair is analysed in detail to show the origin of exchange repulsion and a dynamic Coulomb attraction, which determine its energy aside from the orbital energies. Furthermore, we identify and discuss the two additional effects of secondary orbital relaxation and de-excitations. Rules for reconstructing these four contributions from general excited-state computations are presented and their use is exemplified in three case studies concerned with the relative ordering of the singlet and triplet ππ* and nπ* states of uracil, the large energetic differences between the first singlet and triplet states of the polyacenes, and the assignment of plasmonic states in octatetraene. Finally, we lay out some general ideas for how the knowledge gained could ultimately lead to new design principles for tuning molecular excitation energies as well as for diagnosing possible shortcomings of commonly used electronic structure methods.

Graphical abstract: Toward an understanding of electronic excitation energies beyond the molecular orbital picture

Supplementary files

Article information

Article type
Perspective
Submitted
22 ינו 2020
Accepted
27 פבר 2020
First published
27 פבר 2020

Phys. Chem. Chem. Phys., 2020,22, 6058-6080

Toward an understanding of electronic excitation energies beyond the molecular orbital picture

P. Kimber and F. Plasser, Phys. Chem. Chem. Phys., 2020, 22, 6058 DOI: 10.1039/D0CP00369G

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements