The effects of pi-acceptor and pi-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 effe cts as a function of substitution have been evaluated. Interestingly, the o bserved electronic effects are quite dependent on the constitution of the e nyne framework. In the case of tetraynes 2a-c, acceptor substituted 2b show s an additional low energy absorption in the UV-vis spectrum as compared to 2a and 2c. In contrast, little difference in the electronic characteristic s of 4a-b is detected. The X-ray crystallographic analysis of 4a is also de scribed. (C), 2001 Elsevier Science Ltd. All rights reserved.