thank you very much for the link and the pdf. However, both do not include the structure of this particular dye... Other structures are included but Atto 633 is missing...
The structure is also not present in the 2013/2015 catalogue. It seems it is covered by patent and not published (that is unfortunately quite common among the commercial dye manufacturers). However, I am almost sure it will be a 10-carbo-pyronin derivative. Depends on how precisely you need to know the structure... If it is important to you, than you may estimate it from the patents of the ATTO company (and MPI in Gottingen: http://www.mpibpc.mpg.de/en ) and/or to buy a sample and analyze it by yourself (2D NMR and MS bay be enough to solve the issue).