Changing a value to datetime c#

Question

I am trying to change a value selected in a drop down list to a datetime. The values bound to the drop down list are from a Date column under a datetime2 type, however they change when bound to the drop down list. When the date in the drop down list is selected it should populate a gridview according to the value, but because the format is changed the 'where' clause in my sql statement is invalid.

 

My code is as follows:

protected void DropDownList2_SelectedIndexChanged(object sener, EventArgs e)
{
String query = "SELECT Stock_Take.Username, Item.ItemID, Item.ItemDesc, Stock_Take_Item.BarQuantity, Stock_Take_Item.StorageQuantity, Stock_Take.StockTakeIDNew FROM Item INNER JOIN Stock_Take_Item ON Item.ItemID = Stock_Take_Item.ItemID INNER JOIN Stock_Take ON Stock_Take_Item.StockTakeIDNew = Stock_Take.StockTakeIDNew where Stock_Take.Username = @USER AND Stock_Take.StockDate = @DATE";
SqlConnection con = new SqlConnection(@"Data Source=(local)\;Initial Catalog=SmallBatch;Integrated Security=True;");
con.Open();
SqlCommand cmd = new SqlCommand(query, con);
DropDownList2.SelectedValue.GetType();
cmd.Parameters.Add("@USER", SqlDbType.VarChar).Value = DropDownList1.SelectedValue;
var date = DateTime.ParseExact(DropDownList2.SelectedValue, "yyyy/MM/dd hh:mm:ss", null);
cmd.Parameters.Add("@DATE", SqlDbType.DateTime).Value = date;
// DateTime date = Convert.ToDateTime(DropDownList2.SelectedValue.ToString());
SqlDataReader reader = cmd.ExecuteReader();
GridView1.DataSource = reader;
GridView1.DataBind();
con.Close();
}

An error is throwing on the line var date = DateTime.ParseExact 'String was not recognized as valid DateTime'