The effects of π-acceptor and π-donor substitution in cross-conjugated enynes

Donor (p-NMe2C6H4) and acceptor (p-NO2C6H4) substitution has been appended onto two different cross-conjugated enyne scaffolds and the electronic effects as a function of substitution have been evaluated. Interestingly, the observed electronic effects are quite dependent on the constitution of the enyne framework. In the case of tetraynes 2a–c, acceptor substituted 2b shows an additional low energy absorption in the UV–vis spectrum as compared to 2a and 2c. In contrast, little difference in the electronic characteristics of 4a–b is detected. The X-ray crystallographic analysis of 4a is also described.