Rebuked Sun's first cool journalist (7)
I believe the answer is:
scolded
'rebuked' is the definition.
('scold' can be a synonym of 'rebuke')
'sun's first cool journalist' is the wordplay.
'sun's first' becomes 's' (1st letter of 'sun').
'cool' becomes 'cold' (associated in meaning).
'journalist' becomes 'ed' (short for editor).
's'+'cold'+'ed'='SCOLDED'
(Other definitions for scolded that I've seen before include "Rebuked angrily" , "Berated" , "Told off" .)