From 2,5-Diformyl-1,4-dihydropyrrolo[3,2‑b]pyrroles to Quadrupolar, Centrosymmetric Two-Photon-Absorbing A–D–A Dyes

An original approach has been developed for the insertion of formyl substituents at positions 2 and 5 of 1,4-dihydropyrrolo­[3,2-b]­pyrroles by conversion of thiazol-2-yl substituents. The synthetic utility of these formyl groups was investigated, and a series of centrosymmetric A−π–D−π–A frameworks were constructed. The two-photon absorption of the quadrupolar pyrrolo­[3,2-b]­pyrrole possessing two dicyanovinylidene flanking groups is attributed to an S0 → (S1) → S4 transition which has a large TPA cross-section (1300 GM) for a molecule of this size.