Objection 1. It would seem that the damned never repent of the evil they have done. For Bernard says on the Canticle [Cf. De Consideratione v, 12; De Gratia et Libero Arbitrio ix] that "the damned ever consent to the evil they have done." Therefore they never repent of the sins they have committed.
Objection 2. Further, to wish one had not sinned is a good will. But the damned will never have a good will. Therefore the damned will never wish they had not sinned: and thus the same conclusion follows as above.
Objection 3. Further, according to Damascene (De Fide Orth. ii), "death is to man what their fall was to the angels." But the angel's will is irrevocable after his fall, so that he cannot withdraw from the choice whereby he previously sinned [Cf. I, 64, 2]. Therefore the damned also cannot repent of the sins committed by them.
Objection 4. Further, the wickedness of the damned in hell will be greater than that of sinners in the world. Now in this world some sinners repent not of the sins they have committed, either through blindness of mind, as heretics, or through obstinacy, as those "who are glad when they have done evil, and rejoice in most wicked things" (Proverbs 2:14). Therefore, etc.
On the contrary, It is said of the damned (Wisdom 5:3): "Repenting within themselves [Vulgate: 'Saying within themselves, repenting']."
Further, the Philosopher says (Ethic. ix, 4) that "the wicked are full of repentance; for afterwards they are sorry for that in which previously they took pleasure." Therefore the damned, being most wicked, repent all the more.
I answer that, A person may repent of sin in two ways: in one way directly, in another way indirectly. He repents of a sin directly who hates sin as such: and he repents indirectly who hates it on account of something connected with it, for instance punishment or something of that kind. Accordingly the wicked will not repent of their sins directly, because consent in the malice of sin will remain in them; but they will repent indirectly, inasmuch as they will suffer from the punishment inflicted on them for sin.
Reply to Objection 1. The damned will wickedness, but shun punishment: and thus indirectly they repent of wickedness committed.
Reply to Objection 2. To wish one had not sinned on account of the shamefulness of vice is a good will: but this will not be in the wicked.
Reply to Objection 3. It will be possible for the damned to repent of their sins without turning their will away from sin, because in their sins they will shun, not what they heretofore desired, but something else, namely the punishment.
Reply to Objection 4. However obstinate men may be in this world, they repent of the sins indirectly, if they be punished for them. Thus Augustine says (Q83, qu. 36): "We see the most savage beasts are deterred from the greatest pleasures by fear of pain."
Source: Summa Theologica (New Advent)