A fluorescent dithiadiazolyl radical: structure and optical properties of phenanthrenyl dithiadiazolyl in solution and polymer composites

Abstract

The phenanthrene-functionalised dithiadiazolyl radical 2 provides a rare example of a fluorescent radical, exhibiting bright blue fluorescence (410 nm) in solution (MeCN: Φ_F = 0.11). The indirect participation of the radical electron in the fluorescence process is supported by (i) TD-DFT studies and (ii) the observation that the diamagnetic salt [2][GaCl₄] also exhibits a similar broad emission at 410 nm. The large Stokes shift appears associated with significant molecular relaxation in the excited state, evidenced by the solvent-independent nature of the absorption profile but marked solvent-dependent emission spectrum. Incorporation of 2 into polymer matrices such as PMMA or polystyrene leads to substantial enhancement in air stability with evidence of efficient emission quenching at higher w/w radical : polymer ratios.