Two-photon absorption of perylene-3,4,9,10-tetracarboxylic acid diimides: Effect of substituents in the bay

Improving the efficiency of photon upconversion in small organic molecules is a challenge where the molecular framework of perylene-3,4,9,10-tetracarboxylic acid diimides (PDIs) can provide meaningful achievements. To disentangle the different factors that can affect the n6onlinear optical response of such framework we present a systematic study of the two-photon absorption (TPA) properties of substituted PDIs addressing effects such as distortion from planarity, inductive vs. conjugative substituents, symmetric vs. asymmetric substitution of the bay positions and electron donor (D) vs. acceptor (A) nature of the bay substituents. The best performance in terms of nonlinear absorption was found in tetra-phenoxy bay-substituted PDIs with an A-PDI-A architecture that shows a TPA cross-section one order of magnitude higher than that of planar unsubstituted PDI, despite its distortion from planarity. This study constitutes a paradigmatic example of twisted core PDIs with enhanced optical properties.