A photochromic compound: comprising: at least one photochromic group chosen from a pyran, an oxazine, and a fulgide; and at least one lengthening agent attached to the at least one photochromic group, wherein the at least one lengthening agent is chosen from: 4-(4-fluoro-phenoxycarbonyloxy)-piperidin-1-yl; 4-(biphenyl-4-carbonyloxy)-piperidin-1-yl; 4-(naphthalene-2-carbonyloxy)-piperidin-1-yl; 4-(4-pentadecafluoroheptyloxy-phenylcarbamoyl)-benzyloxy; 4-(3-piperidin-4-yl-propyl)-piperidin-1-yl; biphenyl-4,4'-dicarboxylic acid bis-[1-Name of PC]-piperidin-4-yl] ester, or chosen form: (a) 3-phenyl-3-(4-(4-piperidinopiperidino)phenyl)-13,13-dimethyl-indeno[2',3':3,4]naphtho[1,2-b]pyran; (b) 3-phenyl-3-(4-(4-phenylpiperazine)phenyl)-13,13-dimethyl-indeno[2',3':3,4]naphtho[1,2-b]pyran; (c) 3-phenyl-3-(4-pyrrolidin-1-yl-phenyl)-13,13-dimethyl-6-methoxy-7-(4-phenyl-piperazin-1-yl)indeno[2',3':3,4]naphtho[1,2-b]pyran; (d) 3-phenyl-3-(4-pyrrolidin-1-yl-phenyl)-13,13-dimethyl-6-methoxy-7-([1,4']bipiperidinyl-1 "-yl)indeno[2',3':3,4]naphtho[1,2-b]pyran; (e) 3-phenyl-3-(4-([1,4']bipiperidinyl-1'-yl)phenyl)-13,13-dimethyl-6-methoxy-7-([1,4']bipiperidinyl-1'-yl)indeno[2',3':3,4]naphtho[1,2-b]pyran; (f) 3-phenyl-3-(4-([1,4']bipiperidinyl-1'-yl)phenyl)-13,13-dimethyl-6-methoxy-7-(4-benzylpiperidin-1-yl)indeno[2',3':3,4] naphtho[1,2-b]pyran; (g) 3-phenyl-3-(4-([1,4']bipiperidinyl-1'-yl)phenyl)-13,13-dimethyl-6-methoxy-7-(piperadin-1-yl)indeno[2',3':3,4]naphtho[1,2-b]pyran; (h) 3-phenyl-3-(4-(4-phenyl-piperazin-1-yl)phenyl)-13,13-dimethyl-6-methoxy-7-(4-phenyl-piperazin-1-yl)indeno[2',3':3,4]naphtho[1,2-b]pyran; (i) 1,3,3-trimethyl-6'-(4-ethoxycarbonyl)-piperidin-1-yl)-spiro[indoline-2,3'-3H-naphtho[2,1-b][1,4]oxazine]. comprising: at least one photochromic group chosen from a pyran, an oxazine, and a fulgide; and at least one lengthening agent attached to the at least one photochromic group, wherein the at least one lengthening agent is chosen from: 4-(4-fluoro-phenoxycarbonyloxy)-piperidin-1-yl; 4-(biphenyl-4-carbonyloxy)-piperidin-1-yl; 4-(naphthalene-2-carbonyloxy)-piperidin-1-yl; 4-(4-pentadecafluoroheptyloxy-phenylcarbamoyl)-benzyloxy; 4-(3-piperidin-4-yl-propyl)-piperidin-1-yl; biphenyl-4,4'-dicarboxylic acid bis-[1-Name of PC]-piperidin-4-yl] ester, or at least one photochromic group chosen from a pyran, an oxazine, and a fulgide; and at least one lengthening agent attached to the at least one photochromic group, wherein the at least one lengthening agent is chosen from: 4-(4-fluoro-phenoxycarbonyloxy)-piperidin-1-yl; 4-(biphenyl-4-carbonyloxy)-piperidin-1-yl; 4-(naphthalene-2-carbonyloxy)-piperidin-1-yl; 4-(4-pentadecafluoroheptyloxy-phenylcarbamoyl)-benzyloxy; 4-(3-piperidin-4-yl-propyl)-piperidin-1-yl; biphenyl-4,4'-dicarboxylic acid bis-[1-Name of PC]-piperidin-4-yl] ester, or 4-(4-fluoro-phenoxycarbonyloxy)-piperidin-1-yl; 4-(biphenyl-4-carbonyloxy)-piperidin-1-yl; 4-(naphthalene-2-carbonyloxy)-piperidin-1-yl; 4-(4-pentadecafluoroheptyloxy-phenylcarbamoyl)-benzyloxy; 4-(3-piperidin-4-yl-propyl)-piperidin-1-yl; biphenyl-4,4'-dicarboxylic acid bis-[1-Name of PC]-piperidin-4-yl] ester, or chosen form: (a) 3-phenyl-3-(4-(4-piperidinopiperidino)phenyl)-13,13-dimethyl-indeno[2',3':3,4]naphtho[1,2-b]pyran; (b) 3-phenyl-3-(4-(4-phenylpiperazine)phenyl)-13,13-dimethyl-indeno[2',3':3,4]naphtho[1,2-b]pyran; (c) 3-phenyl-3-(4-pyrrolidin-1-yl-phenyl)-13,13-dimethyl-6-methoxy-7-(4-phenyl-piperazin-1-yl)indeno[2',3':3,4]naphtho[1,2-b]pyran; (d) 3-phenyl-3-(4-pyrrolidin-1-yl-phenyl)-13,13-dimethyl-6-methoxy-7-([1,4']bipiperidinyl-1 "-yl)indeno[2',3':3,4]naphtho[1,2-b]pyran; (e) 3-phenyl-3-(4-([1,4']bipiperidinyl-1'-yl)phenyl)-13,13-dimethyl-6-methoxy-7-([1,4']bipiperidinyl-1'-yl)indeno[2',3':3,4]naphtho[1,2-b]pyran; (f) 3-phenyl-3-(4-([1,4']bipiperidinyl-1'-yl)phenyl)-13,13-dimethyl-6-methoxy-7-(4-benzylpiperidin-1-yl)indeno[2',3':3,4] naphtho[1,2-b]pyran; (g) 3-phenyl-3-(4-([1,4']bipiperidinyl-1'-yl)phenyl)-13,13-dimethyl-6-methoxy-7-(piperadin-1-yl)indeno[2',3':3,4]naphtho[1,2-b]pyran; (h) 3-phenyl-3-(4-(4-phenyl-piperazin-1-yl)phenyl)-13,13-dimethyl-6-methoxy-7-(4-phenyl-piperazin-1-yl)indeno[2',3':3,4]naphtho[1,2-b]pyran; (i) 1,3,3-trimethyl-6'-(4-ethoxycarbonyl)-piperidin-1-yl)-spiro[indoline-2,3'-3H-naphtho[2,1-b][1,4]oxazine]. (a) 3-phenyl-3-(4-(4-piperidinopiperidino)phenyl)-13,13-dimethyl-indeno[2',3':3,4]naphtho[1,2-b]pyran; (b) 3-phenyl-3-(4-(4-phenylpiperazine)phenyl)-13,13-dimethyl-indeno[2',3':3,4]naphtho[1,2-b]pyran; (c) 3-phenyl-3-(4-pyrrolidin-1-yl-phenyl)-13,13-dimethyl-6-methoxy-7-(4-phenyl-piperazin-1-yl)indeno[2',3':3,4]naphtho[1,2-b]pyran; (d) 3-phenyl-3-(4-pyrrolidin-1-yl-phenyl)-13,13-dimethyl-6-methoxy-7-([1,4']bipiperidinyl-1 "-yl)indeno[2',3':3,4]naphtho[1,2-b]pyran; (e) 3-phenyl-3-(4-([1,4']bipiperidinyl-1'-yl)phenyl)-13,13-dimethyl-6-methoxy-7-([1,4']bipiperidinyl-1'-yl)indeno[2',3':3,4]naphtho[1,2-b]pyran; (f) 3-phenyl-3-(4-([1,4']bipiperidinyl-1'-yl)phenyl)-13,13-dimethyl-6-methoxy-7-(4-benzylpiperidin-1-yl)indeno[2',3':3,4] naphtho[1,2-b]pyran; (g) 3-phenyl-3-(4-([1,4']bipiperidinyl-1'-yl)phenyl)-13,13-dimethyl-6-methoxy-7-(piperadin-1-yl)indeno[2',3':3,4]naphtho[1,2-b]pyran; (h) 3-phenyl-3-(4-(4-phenyl-piperazin-1-yl)phenyl)-13,13-dimethyl-6-methoxy-7-(4-phenyl-piperazin-1-yl)indeno[2',3':3,4]naphtho[1,2-b]pyran; (i) 1,3,3-trimethyl-6'-(4-ethoxycarbonyl)-piperidin-1-yl)-spiro[indoline-2,3'-3H-naphtho[2,1-b][1,4]oxazine].