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Motivated by recent synthetic progress to substituted derivatives of this scaffold, we carried out a theoretical and computational analysis with a particular focus on the extent of (anti)aromatic character in the lowest excited states of different multiplicities. We found that the parent <jats:bold>DMCB<\/jats:bold> is non\u2010aromatic in its singlet ground state (S<jats:sub>0<\/jats:sub>), lowest triplet state (T<jats:sub>1<\/jats:sub>), and lowest singlet excited state (S<jats:sub>1<\/jats:sub>), while it is aromatic in its lowest quintet state (Q<jats:sub>1<\/jats:sub>) as this state is represented by a triplet multiplicity cyclobutadiene (<jats:bold>CBD<\/jats:bold>) ring and two uncoupled same\u2010spin methylene radicals. Interestingly, the Q<jats:sub>1<\/jats:sub> state, despite having four unpaired electrons, is placed merely 4.8\u2005eV above S<jats:sub>0<\/jats:sub>, and there is a corresponding singlet tetraradical 0.16\u2005eV above. The <jats:bold>DMCB<\/jats:bold> is potentially a highly useful structural motif for the design of larger molecular entities with interesting optoelectronic properties. Here, we designed macrocycles composed of fused <jats:bold>DMCB<\/jats:bold> units, and according to our computations, two of these have low\u2010lying nonet states (<jats:italic>i.\u2009e<\/jats:italic>., octaradical states) at energies merely 2.40 and 0.37\u2005eV above their S<jats:sub>0<\/jats:sub> states as a result of local H\u00fcckel\u2010 and Baird\u2010aromatic character of individual 6\u03c0\u2010 and 4\u03c0\u2010electron monocycles.<\/jats:p>","DOI":"10.1002\/chem.202303549","type":"journal-article","created":{"date-parts":[[2024,3,3]],"date-time":"2024-03-03T22:05:04Z","timestamp":1709503504000},"update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":5,"title":["3,4\u2010Dimethylenecyclobutene: A Building Block for Design of Macrocycles with Excited State Aromatic Low\u2010Lying High\u2010Spin States"],"prefix":"10.1002","volume":"30","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-5170-8493","authenticated-orcid":false,"given":"Preethanuj","family":"Preethalayam","sequence":"first","affiliation":[{"name":"Department of Chemistry \u2013 \u00c5ngstr\u00f6m Laboratory Uppsala University  Uppsala Sweden"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0642-0914","authenticated-orcid":false,"given":"Juan Carlos","family":"Roldao","sequence":"additional","affiliation":[{"name":"Department of Chemistry \u2013 \u00c5ngstr\u00f6m Laboratory Uppsala University  Uppsala Sweden"},{"name":"Donostia International Physics Center (DIPC)  20018 Donostia Euskadi Spain"},{"name":"University of Bordeaux, CNRS, Bordeaux INP, ISM, UMR 5255  F-33405 Cedex Talence France"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6622-2402","authenticated-orcid":false,"given":"Fr\u00e9d\u00e9ric","family":"Castet","sequence":"additional","affiliation":[{"name":"University of Bordeaux, CNRS, Bordeaux INP, ISM, UMR 5255  F-33405 Cedex Talence France"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8893-7089","authenticated-orcid":false,"given":"David","family":"Casanova","sequence":"additional","affiliation":[{"name":"Donostia International Physics Center (DIPC)  20018 Donostia Euskadi Spain"},{"name":"IKERBASQUE \u2013 Basque Foundation for Science  48009 Bilbao Euskadi Spain"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1928-5494","authenticated-orcid":false,"given":"Slavko","family":"Radenkovi\u0107","sequence":"additional","affiliation":[{"name":"University of Kragujevac Faculty of Science  P. 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