Synthesis and structure of push–pull merocyanines based on barbituric and thiobarbituric acid

Abstract

Two compounds, 1,3-diethyl-5-{(2E,4E)-6-[(E)-1,3,3-trimethylindolin-2-ylidene]hexa-2,4-dien-1-ylidene}pyrimidine-2,4,6(1H,3H,5H)-trione or TMI, C25H29N3O3, and 1,3-diethyl-2-sulfanylidene-5-[2-(1,3,3-trimethylindolin-2-ylidene)ethylidene]dihydropyrimidine-4,6(1H,5H)-dione or DTB, C21H25N3O2S, have been crystallized and studied. These compounds contain the same indole derivative donor group and differ in their acceptor groups (in TMI it contains oxygen in the para position, and in DTB sulfur) and the length of the π-bridge. In both materials, molecules are packed in a herringbone manner with differences in the twist and fold angles. In both structures, the molecules are connected by weak C—H...O and/or C—H...S bonds.