For sauce, remove any stems from chipotle peppers. Place peppers and adobo sauce in a blender. Cover and blend until smooth. Set aside.
Lightly coat an unheated medium saucepan with nonstick cooking spray. Cook onion and garlic in saucepan until tender. Stir in chipotle pepper mixture, ketchup, vinegar, molasses, and Worcestershire sauce. Bring to boiling. Reduce heat and simmer, uncovered, about 10 minutes or until sauce is slightly thickened.
For a charcoal grill, grill chicken on the rack of an uncovered grill directly over medium coals for 12 to 15 minutes or until chicken is no longer pink (170 degrees F), turning once halfway through grilling and brushing with sauce during the last 5 minutes of grilling. (For a gas grill, preheat grill. Reduce heat to medium. Place chicken on grill rack over heat. Cover and grill as above.) Bring remaining sauce to boiling; pass with chicken. Makes 6 servings.