TPA-active D–π–D fluorophores with rigid, planar cores from phenylene to indenofluorene and indolocarbazole

A series of D–π–D quadrupolar fluorophores with systematically varied π-conjugated cores were prepared using the Heck reaction and their single- and two-photon photophysical properties were examined. Introduction of extended π-conjugated cores such as indenofluorene/indolocarbazole was found to induce only small shifts in the absorption and emission maxima versus the phenylene linked fluorophore but greatly enhance their single- and two-photon absorption cross-sections. The effects of positional substitution on the properties of the indolocarbazole derivatives were also investigated.