I do wonder if any one had measured or is aware about absorption of the cis-form (dark form) of the Alexa647 and Cy5??

My question could be also answered with the following experiment:

1- measure absorption of Alexa647 (or Cy5).

2- take the solution from the cuvette and expose it to high power laser until it is completely photobleached.

3- remeasure the absorption spectrum of the photobleached solution.

Unfortunately, I have no proper laser for this experiment.