Blue 3H-naphtho[2,1-b]pyran compounds and use thereof in photochromic articles

1 7 Photochromic 3H-naphtho[2,1-b]pyran compounds corresponding to formula I in which the groups Rto Rand B′ have defined meanings and the use of such photochromic compounds in synthetic resin articles of all types, particularly for ophthalmic purposes. The photochromic 3H-naphtho[2,1-b]pyran derivatives have particularly long-waved absorption maxima in the open form, and when used in photochromic eyeglass lenses, produce essentially blue color tones which have a high darkening capacity.