Animated quartet captured by Dutch portraitist (6)
I believe the answer is:
lively
'animated' is the definition.
(synonyms)
'quartet captured by dutch portraitist' is the wordplay.
'quartet' becomes 'IV' (Roman numerals for four).
'captured by' indicates putting letters inside.
'dutch portraitist' becomes 'Lely' (17th-century artist Peter Lely).
'iv' put within 'lely' is 'LIVELY'.
(Other definitions for lively that I've seen before include "Full of energy and high spirits" , "Full of zest or vigour" , "Animated" , "Full of fun" , "Full of zest and energy" .)