**A Flavone-Based Solvatochromic Probe with A Low Expected Perturbation Impact on the Membrane Physical State**

**Simona Concilio 1,\* , Miriam Di Martino <sup>2</sup> , Anna Maria Nardiello <sup>2</sup> , Barbara Panunzi <sup>3</sup> , Lucia Sessa <sup>2</sup> , Ylenia Miele <sup>4</sup> , Federico Rossi <sup>5</sup> and Stefano Piotto 2,\***


Academic Editors: Prieto Jorge Bañuelos and Ugo Caruso Received: 7 July 2020; Accepted: 28 July 2020; Published: 29 July 2020

**Abstract:** The study of the cell membrane is an ambitious and arduous objective since its physical state is regulated by a series of processes that guarantee its regular functionality. Among the different methods of analysis, fluorescence spectroscopy is a technique of election, non-invasive, and easy to use. Besides, molecular dynamics analysis (MD) on model membranes provides useful information on the possibility of using a new probe, following its positioning in the membrane, and evaluating the possible perturbation of the double layer. In this work, we report the rational design and the synthesis of a new fluorescent solvatochromic probe and its characterization in model membranes. The probe consists of a fluorescent aromatic nucleus of a 3-hydroxyflavone moiety, provided with a saturated chain of 18 carbon atoms and a zwitterionic head so to facilitate the anchoring to the polar heads of the lipid bilayer and avoid the complete internalization. It was possible to study the behavior of the probe in GUV model membranes by MD analysis and fluorescence microscopy, demonstrating that the new probe can efficiently be incorporated in the lipid bilayer, and give a color response, thanks to is solvatochromic properties. Moreover, MD simulation of the probe in the membrane supports the hypothesis of a reduced perturbation of the membrane physical state.

**Keywords:** flavone; solvatochromic probe; membrane
