Source : Webster's Revised Unabridged Dictionary (1913)

Unsuccessful \Un`suc*cess"ful\, a.
   Not successful; not producing the desired event; not
   fortunate; meeting with, or resulting in, failure; unlucky;
   unhappy. -- {Un`suc*cess"ful*ly}, adv. --
   {Un`suc*cess"ful*ness}, n.

Source : WordNet®

unsuccessfully
     adv : without success; "she tried unsuccessfully to persuade him
           to buy a new car" [ant: {successfully}]