π-Conjugated molecules with an even number of π-electrons usually have a closed-shell ground state. However, recent studies have demonstrated that a certain type of molecules could show open-shell singlet ground state and display diradical-like (diradicaloid) behavior. Their electronic structure can be understood in terms of the “diradical character” and “aromaticity” concepts. They display very different electronic properties from traditional closed-shell π-conjugated molecules and could be used as next-generation molecular materials.

This book provides a comprehensive review on the chemistry, physics, and material applications of open-shell singlet diradicaloids. Particularly, it elaborates the fundamental structure–diradical character–electronic property relationships both theoretically and experimentally. The book has been written by leading scientists in the field from Japan, Germany, Spain, Italy, China, and Singapore.

Jishan Wu received his BSc degree in chemistry from Wuhan University, China (1997), MSc degree from Changchun Institute of Applied Chemistry, Chinese Academy of Sciences (2000), and PhD degree from the Max-Planck Institute for Polymer Research (2004). He did his postdoc study at the University of California in Los Angeles (2005–2007) and then joined the Department of Chemistry, National University of Singapore as an assistant professor in 2007. He was promoted to full professor in 2017. Prof. Wu’s major interests include novel π-conjugated systems and supramolecular chemistry. He has co-authored 300+ publications, been listed as one of the highly cited researchers from Clarivate Analytics, and has received more than 20 awards after starting his independent career in Singapore, including the latest National Research Foundation Investigatorship (2019).