<h3>Title</h3>
<p><span style="color: #0000ff;">Excited State Aromaticity and Antiaromaticity: From Scopes to Pitfalls</span></p>
<p><strong><span style="text-decoration: underline;">Abstract</span> :</strong></p>
<p>Use of the excited state aromaticity and antiaromaticity concepts (ESA &amp; ESAA) to rationalize excited state properties and processes has grown rapidly in recent years. <sup>[1-3]</sup> The concepts are often described by Baird's 4n and 4n+2 rules for, respectively, aromaticity and antiaromaticity in the lowest ππ* excited states, and they have been utilized to rationalize various photoreactions, <sup>[4-6]</sup> to explore and design photofunctional molecules, <sup>[7-9]</sup> and to interpret fundamental excited state properties.<sup> [10-14]</sup> The concepts can likely find use in a variety of areas, ranging from astrochemistry and organic synthesis to biophysics and photovoltaics. Examples of such applications will be presented. Yet, simultaneously as the concepts are applied within gradually more areas it is important to explore their limitations, complications and pitfalls so as to avoid improper use; an induced diatropic ring current in the T1 state does not always indicate Baird-aromaticity. Indeed, there are molecules which are Hückel-aromatic in their excited states, <sup>[14,15]</sup> and some quinoidal compounds can be simultaneously Hückel- and Baird-aromatic. <sup>[16,17]</sup> Finally, heterocycles as well as macrocycles with tentative ESA character expose a number of complications, both computationally and conceptually. <sup>[18,19]</sup> Thus, at the same time as we explore and expand the scopes of the ESA &amp; ESAA concepts we also need an improved knowledge on their limitations, complications and pitfalls. The talk will address both aspects.</p>
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