T-Shaped (Donor-pi-)(2)Acceptor-pi-Donor Push-Pull Systems Based on Indan-1,3-dione

Sixteen model (donor-pi-)(2)acceptor-pi-donor [(D-pi-)(2)A-pi-D] molecules with an extraordinary T-shaped arrangement were designed and synthesized. Indan-1,3-dione was employed as a central acceptor with electron donors linked at the C-2, C-4, and C-7 positions. These push-pull molecules represent a first systematic modification of an indan-1,3-dione-fused benzene ring. The structures and properties of all target molecules were investigated by X-ray analysis, electrochemistry, UV/Vis absorption spectroscopy, differential scanning calorimetry, electric-field-induced second-harmonic generation (EFISHG) studies, and DFT calculations. A thorough evaluation of all of the gathered data has been performed, and structure-property relationships were evaluated. Electron donors attached at the C-2 position through systems of various lengths affect the studied properties most significantly. The side donors at C-4 and C-7 can be described as auxiliary and do not dominate the observed properties. However, thiophene is a more efficient donor than N,N-dimethylaniline in this respect. Hence, indan-1,3-dione bearing a piperidylthiophene donor connected through a propenylidene spacer at C-2 completed with two side thiophen-2-ylethynyl branches at C-4 and C-7 showed the highest figure of merit among the studied properties.