Hi
Exit MBCF0002 helps to populate the SGTXT (Short Text) in MM doc and the same gets passed on to BSEG-SGTXT automatically
you can then write a subst in FI to copy it from SGTXT to desired field
Other options are
MB_DOCUMENT_BADI BAdIs During Creation of a Material Document
MB_DOCUMENT_BADI_SAP BADI for Creation and Changing of a Material Document
You can use FI BTE event 1120,
there could be lot many options.. depends on what you want
br, Ajay M