(a, b) UV–vis absorption spectra of mixtures of 1a, 2a, and Cs2CO3 in DMSO (path length = 1 cm) at concentrations of (a) 6 × 10−4 M and (b) 0.1 M for each species. The inset of (b) shows the formation of a yellow compound (proposed EDA complex) upon mixing of 1a, 2a, and Cs2CO3. (c) Time-dependent DFT calculations to predict UV–vis absorptions of the EDA complex. (d) Proposed mechanism for visible-light induced C–S cross-coupling.