说动 is a verb-resultative compound:
说 'speak' +
动 'move (someone)' = 'talk + result of being moved' = 'successfully persuade'. The
动 here is the resultative marker — like
看见 (look + see),
找到 (look for + find),
说动 emphasizes the success of the persuasion, not just the trying. To say only the trying, use
劝 (quàn) or
说服 (shuōfú).
