Bob;

No, AFAIK, they do not. Of course, that would put them into the UV region and we do not routinely measure there. My tests and ours at work normally ran from 400 - 700 nm. However, IR dyes that sensitize AgX at 800 - 900 nm do not show secondary peaks at 400 or so, and I am basing my assumption on these longer chain examples as well as the more common dyes.

Ed;

Symmetry is not needed as much as conjugation, that is the double bonds shown. Symmetry is often there because a given molecule is easy to make.

PE