Fluorine-free diarylethene photochromic compounds

A photochromic compound comprising at least one of a compound of Formula (I), an activated analog of the compound according to Formula (I), and a dyotropic rearrangement of the compound according to Formula (I):

• wherein A1 and A2 are independently selected from substituents having Formula (Ia) and substituents having Formula (Ib), with the proviso that at least one of A1 and A2 is a substituent having Formula (Ia):
• wherein
• each W is independently selected from Cl, Br, and I;
• each Y is independently selected from S, O, and NR6;
• each Z is independently selected from N and CR7;
• each R1 is independently selected from O, S, C═C, C≡C, OC(═O), C(═O)O, C(═O)S, SC(═O), C(═O)NH, NHC(═O), C(═S)NH, NHC(═S), NHC(═O)NH, and NHC(═S)NH;
• each R2 is independently selected from H, C1-6alkyl, N(R8)2, N+H(R8)2, and any of the foregoing linked to R3 via an additional R1 group;
• each R3 is independently a bond, linear or branched C1-20alkylene, or linear or branched (OCH2CH2)n, where n is an integer in the range of 1 to 20;
• each R4 is independently selected from C1-8alkyl, C4-8cycloalkyl, C1-12alkoxy, C≡CR7, and cyano;
• and
• each m is independently 1 to 5;
• wherein ring B has the formula
• wherein
• X is CH2 and R5 is a bond or unsubstituted or substituted C1-2 alkylene, or X is carbonyl and R5 is O, NH, or NR8;
• wherein each R6, R7, and R8 is independently selected from H, C1-6 alkyl, and aryl;
• and with the proviso that if ring B is
• Y is S, Z is CH, R1 is C(═O)O, R3 is linear or branched C1-20alkylene, and R2 is H or C1-6alkyl, then R2 and R3 collectively are other than C18alkyl.