String to datetime conversion?

try
       {
           string excelConnectionString = string.Format("Provider=Microsoft.ACE.OLEDB.12.0;Data Source={0};Extended Properties='Excel 8.0;HDR=Yes'", path);
               connection = new OleDbConnection();
               connection.ConnectionString = excelConnectionString;
        OleDbCommand command = new OleDbCommand("select * from [Sheet1$]", connection);
               connection.Open();
               DbDataReader dr = command.ExecuteReader();
       DataTable table = new DataTable("Customers");
       table.Load(dr);
       table.Columns.Add("UploadedFromDate", typeof(DateTime));
       table.Columns.Add("UploadedToDate", typeof(DateTime));
       table.Columns.Add("CreatedDate", typeof(DateTime));

           foreach (DataRow row in table.Rows)
           {

               row["UploadedFromDate"] = DateTime.ParseExact(txtfromdate.Text.Trim(), "yyyy-MM-dd HH:mm tt", null);
               row["UploadedToDate"] = DateTime.ParseExact(txttodate.Text.Trim(), "yyyy-MM-dd HH:mm tt", null);
               row["CreatedDate"] = System.DateTime.Now;
           }