10624 | J. Mater. Chem. C, 2021, 9, 10624–10646 This journal is © The Royal Society of Chemistry 2021 Cite this: J. Mater. Chem. C, 2021, 9, 10624 Insights into the magnetism and phase transitions of organic radical-based materials Merce ` Deumal, * Sergi Vela, Maria Fumanal, Jordi Ribas-Arino * and Juan J. Novoa* Organic radicals have been consistently regarded as promising building blocks for the next generation of applied materials. Multiple radical families have been developed and characterized in the last decades, fostered by the ever-growing capabilities of organic synthesis. Thiazyl-, spiro-biphenalenyl-, 1,2,4-benzotriazinyl-, and nitroxide-based radicals have furnished striking examples of metal-free switchable materials, whose phase transitions are accompanied by changes in the magnetic, optical and/or electrical response. While similar in origin, their actual mechanism, driving force(s), and spin state stabilities often depict a different landscape. Fundamental knowledge on such aspects, as well as on the underlying network of spin exchange couplings and non-covalent interactions (including pancake bonding), are key to understand their spin transition, and the tailored modification of their properties. These complex features cannot be extracted based solely on experimental input, but rely on a computational interpretation. In this Perspective article, we discuss the insight gained from computational modelling into the magnetism and phase transitions of organic radical-based materials. We focus on the key importance of dynamic effects due to the labile nature of p-stack interactions assembling those materials, the structural distortions driven by spin changes, the coupling between electronic structure and order–disorder transitions, and the dependence of spin correlation upon temperature. All these phenomena uncovered by simulations should assist in the rational design of new dynamic organic crystals. Departament de Cie `ncia de Materials i Quı ´mica Fı ´sica and IQTCUB, Universitat de Barcelona, Martı ´ i Franque `s 1, E-08028, Barcelona, Spain. E-mail: merce.deumal@ub.edu, j.ribas@ub.edu, juan.novoa@ub.edu Merce ` Deumal Dr Merce ` Deumal is full Professor at Seccio´ de Quı ´mica Fı ´sica (Universitat de Barcelona), where she develops her tasks both as a researcher and lecturer at BSc, MSc and PhD levels. She is the local coordinator at UB of the interuniversity doctoral program on ‘Theoretical Chemistry and Computational Modeling’, and belongs to ‘Institut de Quı ´mica Teo`rica i Computacional’ (awarded as Unit of Excellence Marı ´a de Maeztu), and ‘Xarxa de Refere `ncia en Quı ´mica Teo`rica i Computacional’. Her research is framed in the field of Material Science and Computational Chemistry, and focuses on the rational design of advanced multifunctional molecular materials using multiscale simulation methods, which encompass the use of ab initio quantum mechanics, molecular dynamics, Monte Carlo, statistical mechanics, machine learning and solid state calculations. Sergi Vela Dr Sergi Vela graduated with a chemistry degree from the University of Barcelona in 2009. He obtained his PhD in 2014 under the supervision of Prof. Juan J. Novoa and Prof. Merce ` Deumal. Then, he joined the Laboratoire de Chimie Quantique at the University of Strasbourg, where he worked in the computational modelling of Spin Crossover materials with Prof. Vincent Robert. In 2018, he joined the group of Prof. Cle ´mence Corminboeuf at EPFL under a Marie Sklodowska-Curie Fellowship, to work in the study of molecular photo-switches, and on the design and discovery of novel materials within the Marvel program. Received 25th March 2021, Accepted 1st June 2021 DOI: 10.1039/d1tc01376a rsc.li/materials-c Journal of Materials Chemistry C PERSPECTIVE Published on 10 June 2021. Downloaded on 9/14/2021 2:09:45 PM. View Article Online View Journal | View Issue