Strong Charge‐Transfer Chromophores from [2+2] Cycloadditions of TCNE and TCNQ to Peripheral Donor‐Substituted Alkynes
Peripheral donor-substituted N,N-dimethyl-4-[(7-nitrobenzo[c][1,2,5]thiadiazol-4-yl)ethynyl]aniline (1a), 4-(benzo[c][1,2,5]thiadiazol-4-ylethynyl)-N,N-dimethylaniline (1b), and 4,4′-{benzo[c][1,2,5]thiadiazole-4,7-diylbis(ethyne-2,1-diyl)}bis(N,N-dimethylaniline) (2) were prepared by Sonogashira cross-coupling reactions. Compounds 1a, 1b, and 2 subsequently reacted with tetracyanoethylene (TCNE) or 7,7,8,8-tetracyanoquinodimethane (TCNQ) to afford the charge-transfer chromophores 3–8. X-ray crystallographic analysis revealed the nonplanarity of these donor–acceptor (D–A) chromophores. Cyclic voltammetry (CV) exhibited a multistep reduction wave. UV/Vis spectra and theoretical calculations identified efficient intramolecular charge-transfer interactions. Moreover, scanning electron microscopy (SEM) showed the morphology transition and reconstruction process of 5 from 0D hollow nanospheres to 1D tubular microstructures.