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 S 0 → (S 1 ) → S 4 transition which has a large TPA cross-section (1300 GM) for a molecule of this size.