CREATE TABLE #Example
(
    Product     character(3) PRIMARY KEY,
    TheDate     datetime2(3) NOT NULL
);

INSERT #Example
    (Product, TheDate)
VALUES
    (CONVERT(character(3), 'pd0'), CONVERT(datetime2(3), '2012-08-11 18:45:55.780', 121)),
    (CONVERT(character(3), 'Pd1'), CONVERT(datetime2(3), '2012-08-11 18:55:17.020', 121)),
    (CONVERT(character(3), 'pd2'), CONVERT(datetime2(3), '2012-08-11 19:06:58.623', 121)),
    (CONVERT(character(3), 'pd3'), CONVERT(datetime2(3), '2012-08-18 12:00:01.193', 121)),
    (CONVERT(character(3), 'pd4'), CONVERT(datetime2(3), '2012-08-25 12:13:04.077', 121)),
    (CONVERT(character(3), 'pd5'), CONVERT(datetime2(3), '2012-08-25 17:28:30.347', 121)),
    (CONVERT(character(3), 'pd6'), CONVERT(datetime2(3), '2012-08-25 18:23:16.473', 121)),
    (CONVERT(character(3), 'pd7'), CONVERT(datetime2(3), '2012-09-18 18:29:58.360', 121));

-- Demo index
CREATE INDEX nc1 ON #Example (TheDate);

-- Dave's solution
SELECT
    e.Product,
    e.TheDate
FROM #Example AS e
WHERE
    e.TheDate >= CONVERT(datetime2(3), '20120811', 112)
    AND e.TheDate < CONVERT(datetime2(3), '20120819', 112);

-- Also works, but not as efficient
SELECT
    e.Product,
    e.TheDate
FROM #Example AS e
WHERE
    CONVERT(date, e.TheDate) 
        BETWEEN 
            CONVERT(date, '2012-08-11', 121) 
        AND CONVERT(date, '2012-08-18', 121);