X-ray generated exciplexes of diphenylacetylenes with CF3 or OMe substituent group

This work reports the investigation of six synthesized diphenylacetylenes (DPAs) with systematically varied position of donor (-OMe) or acceptor (-CF₃) substituent group and unsubstituted DPA. DPAs under study are found to have different luminescence properties, namely, luminescence lifetimes vary from less than 200 ps to 0.96 ns, and quantum yields vary from 0.005 to 0.45. Nevertheless, all of substituted DPAs efficiently form exciplexes with N,N-dimethylaniline under X-ray irradiation of n-dodecane solution via radical ion pair recombination. The exciplex lifetime and the position of exciplex emission band depend strongly on the nature of the substituent group. For instance, the acceptor groups shift exciplex emission bathochromically, compared to unsubstituted DPA, whereas the donor groups shift it hypsochromically. The shifting of the exciplex emission is found to correlate with electron affinity of corresponded substituted DPA. Electron affinities are obtained by means of quantum chemical calculations at CAM-B3LYP level of theory and 6-31+G(d,p) basis set.