Synthesis, structure, and electronic and photophysical properties of two- and three-layered [3.3]Paracyclophane-based donor-acceptor systems (1)

Figure presented. The synthesis, structural, redox, and photophysical properties of the two- and three-layered donor-acceptor (D-A) type [3.3]paracyclophanes ([3.3]PCPs) are described. The synthesis of the two- and three-layered [3.3]PCPs 1 and 2 containing 2,1,3-benzothiadiazole (BTD) as an acceptor was achieved by the (p-ethylbenzenesulfonyl)methyl isocyanide coupling method. The cyclic voltammograms of 1 and 2 along with those of respective dione precursors 5 and 7 clearly indicate that the presence of the -CH ₂COCH₂- bridge interferes with the electronic interactions between the BTD and the benzene rings, suggesting the importance of the through-bond interaction in the ground state. In sharp contrast, the UV/vis spectra of 1 and 5 as well as those of 2 and 7 exhibit similar bands regardless of the presence of the -CH₂COCH₂- or -CH ₂CH₂CH₂- bridges, indicating that the charge-transfer (CT) interaction is mainly responsible for the through-space interaction. The two-layered PCPs, 5 and 1, show broad structureless fluorescence bands at the same position of 468 nm, while those of the three-layered PCPs, 7 and 2, appear at 501 and 496 nm, respectively, with lower quantum yields compared to those of the two-layered PCPs probably due to the stronger intramolecular CT interaction of the three-layered PCPs in the ground state.