Yue Zhang, Xinyi Zeng, Andrey V Zibarev, Hui Wang
Chalcogen bonding (ChB) is promising for molecular recognition and sensing of Lewis bases (LBs). Tunable optically-detected ChB-based recognition requires understanding how the nature of the chalcogen influences both the ChB-forming interactions and the resulting optical responses. 3,4-Dicyanofuroxan (DCF) and its heavier chalcogen congeners (E-DCF; E = S, Se, Te) are studied with molecular electrostatic potential, density functional theory, its time-dependent incarnation, quantum theory of atoms in molecules, and hole-electron analysis as suitable recognition and sensing platforms. All compounds feature electrostatic π-holes. Unlike E-DCF with two non-equivalent σ-holes, DCF exhibits only one hole. In ChB-based LB recognition and sensing, DCF acts as a π-hole donor, while with E-DCF the recognition is switched to σ-hole interactions, which results in a distinct optical response. DCF selectively produces charge-transfer (CT) excitations in the case of halide anions, generating pronounced red shifts in electronic absorption spectra in the UV-vis region. In contrast, E-DCF mainly preserves locally excited (LE) character, producing intensity modulation and moderate spectral band shifts. Highly polarizable [I]- breaks the trend, inducing strong CT character in the case of [S-DCF⋯I]- and mixed CT/LE character in the case of [Se-DCF⋯I]-, demonstrating that the polarizability can overcome chalcogen-dependent orbital constraints. The chalcogen contribution to the holes' spatial distributions positively correlates with spectral red shifts, linking excited-state structure to optical selectivity. Together with solvent-dependent differences, these findings demonstrate that the ChB-based interactions of E-DCF (E = O, S, Se, Te) with LBs are π-hole ↔ σ-hole switchable, providing theoretical guidance for their potential applications in tunable molecular recognition and sensing responses.