Cheerful article penned by disturbed genius (8)
I believe the answer is:
sanguine
'cheerful' is the definition.
(I've seen this before)
'article penned by disturbed genius' is the wordplay.
'article' becomes 'an' (indefinite article).
'penned by' means one lot of letters goes inside another.
'disturbed' is an anagram indicator.
'genius' with letters rearranged gives 'sguine'.
'an' inserted within 'sguine' is 'SANGUINE'.
(Other definitions for sanguine that I've seen before include "Confidently optimistic and cheerful" , "Hopeful or optimistic" , "Cheerfully optimistic" , "Assured, optimistic" , "Confident < , or > ruddy" .)