The interconnection of two positive charges by conjugation and cross‐conjugation in bis‐quinolinium ethynyls

1,4-Diethynylbenzene was used as conjugated all-carbon and rigid spacer between the 2-, 3- and 4-positions of two 1-methylquinolinium rings. Thus, for a systematic study, a series of dicationic salts with 2,2-, 3,3-, 4,4-, 3,2-, and 3,4-interconnections of the two positive charges was prepared, in which all even-numbered substitution patterns are conjugated, and all odd-numbered substitution patterns are cross-conjugated. As a consequence, conjugated/conjugated, cross-conjugated/cross-conjugated, and conjugated/cross-conjugated dications have been prepared. The different combinations result in considerably different charge distributions of the positive charges within the π-electron systems according to the rules of resonance which translate into different DFT-calculated frontier orbital profiles and spectroscopic properties such as 13C NMR chemical shifts, IR and Raman absorptions, and the measured as well as calculated UV/Vis spectra.