What do you think is Anne's purpose in keeping a detailed diary while in seclusion and hiding from the Nazi's?

Anne's purpose in keeping a detailed diary while in seclusion was to alleviate boredom.

Explanation:

To be put into hiding for as long as Anne and her family would have been tedious and boring at the same time. With only the few people she saw everyday, she would soon grow bored of the whole situation. Since she could not go outside, she kept a diary of her thoughts, fears, and dreams to see into her inner self possibly to look back on when she was free or to share with other survivors.