“…To achieve sensitive and reliable fluorescence detection in complex biological systems or in living organisms, and thus considering biomedical applications for xanthene-based fluorophores, current research efforts are primarily devoted to the design of rhodamines and related compounds having absorption/emission maxima in the spectral range 650-900 nm [15], often called "therapeutic optical window" (or NIR-1 window) [16]. The relevant strategies implemented to achieve this goal can be classified into two main categories: (1) the extension of the p-conjugated system either through the introduction of various fused aromatic rings within the xanthene core [17][18][19][20][21][22][23][24][25][26][27][28][29][30] or the installation of a dimethine bridge connecting another chromophore unit (e.g., dihydroxanthene-hemicyanine fused dyes) [31,32], and (2) the replacement of the 10-position O atom of xanthene by a group 14 element (i.e., C, Si, or Ge) [33][34][35][36] or an oxidized-heteroatom such as B(OH) 2 [37], P(O)R [38,39], P(O)OR [40], or Te(O) [41]. This latter approach is particularly attractive because it produces dyes with significantly red-shifted absorption and fluorescence maxima, typically around or above 650 nm, and keeping compact structures and small molecular weights.…”