what about this
--// Convert NVARCHAR to DATETIME
DECLARE @date DATETIME = (SELECT convert(DATETIME, '2013-08-29 13:55:48', 120))
--// Convert DATETIME to custom NVARCHAR FORMAT
SELECT
RIGHT('00'+ CAST(DAY(@date) AS NVARCHAR),2) + '-' +
RIGHT('00'+ CAST(MONTH(@date) AS NVARCHAR),2) + '-' +
CAST(YEAR(@date) AS NVARCHAR) + ' ' +
CAST(CONVERT(TIME,@date) AS NVARCHAR)
result: '29-08-2013 13:55:48.0000000'