G7 and Db7 share the same tritone (B and F). Because the tritone is what defines a dominant's pull, both chords resolve equally well to C. Swap G7 for Db7 in a ii-V-I and you get Dm7 → Db7 → Cmaj7 — a chromatic bass line that's pure jazz.

Why it works

Dominants resolve via their tritone. Two dominant chords a tritone apart share the same tritone (just inverted). So they're functionally interchangeable, even though their roots are 6 frets apart.

When to use it

• Reharmonize a tired ii-V-I to sound fresh
• Create chromatic bass motion (Dm7 → Db7 → Cmaj7)
• Extend a turnaround at the end of a tune