Boron-substituted Xanthene dyes for bioimaging applications

Xanthene dyes like fluoresceins and rhodamines have been intensively studied since their first<br/>synthesis in 1871 and 1887 [1]. An interesting way of extending their absorption and emission<br/>wavelengths is to substitute the central oxygen by a group 14, 15 or 16 element such as Si, P,<br/>C or Se [2]. Boron-substituted xanthenes have been synthetised but are yet to be furtherly<br/>investigated. Tricoordinated boron-substituted fluoresceins displayed the largest wavelengths<br/>shifts amongst heteroatoms, allowing emission in the near-infrared region, despite low<br/>fluorescence quantum yields [3]. The vacant p orbital of the tricoordinated boron atom allows<br/>p-π* interactions, stabilising the LUMO, which results in an increase of the wavelength.<br/>Improving the synthesis, increasing the quantum yields and extending the process to<br/>rhodamines and rhodols opens a path towards several applications such as bioimaging, TADF,<br/>pH sensors… As these molecules are Lewis acids, their properties in tetracoordinated form<br/>are heavily modified, depending on the Lewis base used, making them versatile fluorophores<br/>for sensing applications.<br/>In this poster, we will present the future synthesis of new boron-substituted xanthene dyes,<br/>and the first theoretical results obtained.