Concern, though not about one in isolation (8)
I believe the answer is:
solitude
'isolation' is the definition.
(solitude is a kind of isolation)
'concern though not about one' is the wordplay.
I cannot really see how this works, but
'not' could be 'o' (I've seen this in other clues) and 'o' is found within the answer.
'one' could be 'li' (I've seen this in other clues) and 'li' is found in the answer.
This may be the basis of clue (or it may be nonsense).
'in' acts as a link.
Can you help me to learn more?
(Other definitions for solitude that I've seen before include "State of being alone without companions" , "State of aloneness" , "Isolated state - slide out (anag)" , "Lou diets in isolation" , "Privacy" .)