Ethynyl‐Bridged Bis‐quinolinium Dyes: Studies of the Dependence of Different Types of Conjugation on Spectroscopic Properties

Abstract

Dicationic bis-quinolinium salts possessing different types of conjugation are presented in which the hetareniums are separated by acetylenic or 1,4-diethynylbenzene spacers. Crossconjugation is induced by interconnections via the 3-positions of the heteroareniums, and conjugation is realized by 2,2/2,4/ 4,4-interconnections. We also synthesized mixed cross-conjugated/conjugated 2,3/4,3-interconnected species. The different types of conjugation determine the charge distribution according to the rules of resonance which translate into characteristic 13 C NMR as well as UV-Vis-spectroscopic properties, LUMO geometries, and chemical properties. We found that the triple bond's resonance frequencies are sensitive 13 C NMR spectroscopic indicators for the type of conjugation. Combining crossconjugated and conjugated structure elements of dicationic bis-quinolinium dyes via triple bonds without additional benzene spacer results in considerable bathochromic shifts of the UV-Vis absorption maxima [Δλ max � 100 nm]. A charge transfer was calculated from the HOMO of the conjugated into the LUMO of the cross-conjugated partial structure.

Highly Sensitive Switchable Sensors for Hydroxide on Glass Surfaces Based on Isoquinolinium‐Quinolinium‐substituted Acetylenes

“…Interesting perspectives arise when both types of conjugation are combined in a single molecule. Depending on the type of interconnection, different physical and chemical properties result, regardless of whether the hetarenium rings are separated by conjugated spacers or not [9,10] . We show here that the inclusion of isoquinolinium moieties in the architecture of bis‐heteroaryl‐substituted acetylenes on the side of quinoliniums opens up additional perspectives and applications, since the positive charges of quinolinium are localized at the “active” positions 1, 2, 4, 8a, but of isoquinolinium at 1, 2, 3, 4a and in both cases in the annelated phenyl ring (Figure 2).…”