Ideally, as-fresh-as-you-can-get-it, organic, fresh fruits and vegetables is recommended for detoxification purposes.
You can include organic frozen fruit (berries mainly) as a small portion of your diet, this should have no negative impact.
Fresh to semi-fresh vegetables are usually available all-year-round at the grocery stores and are recommended instead of frozen vegetables.
Organic frozen vegetables, however, are certainly still fine for the occasional treat meal. Be sure they're free of additives and preservatives (which you find more prevalent with frozen vegetables).