A photochromic material of indeno [2',3':3,4]naphtho[1,2-b]pyran structure, characterized in that it comprises: - a nitrogen containing substituent selected from (i) -N(R 15)R 16, R 15 and R 16 each being independently chosen from C 1 -C 8 alkyl, C 1 -C 8 alkylaryl, C 3 -C 20 cycloalkyl, C 4 -C 20 bicycloalkyl, C 5 -C 20 tricycloalkyl or C 1 -C 20 alkoxyalkyl and said aryl group being phenyl or naphthyl; (ii) a nitrogen containing ring represented by the following graphic formula: wherein each Y being independently chosen for each occurrence from -CH 2 -, -CH(R 17)-, -C(R 17)(R 17)-, -CH(aryl)-, -C(aryl) 2 - or -C(R 17)(aryl)-; X being -Y-, -O-, -S-, -NH-, -N(R 17)- or -N(aryl)-; R 17 being C 1 -C 6 alkyl; said aryl group being phenyl or naphthyl, m being chosen from the integer 1, 2 or 3 and p being chosen from the integer 0, 1, 2 or 3; provided that when p is 0, X is Y; (iii) a group represented by one of the following graphic formulae: wherein each R 19, R 20 and R 21 being chosen independently for each occurrence in each formula from hydrogen, C 1 -C 5 alkyl, phenyl or naphthyl; or the groups R 19 and R 20 together form a ring of 5 to 8 carbon atoms; R 18 being chosen independently for each occurrence from C 1 -C 6 alkyl, C 1-6 alkoxy, fluoro or chloro and n being chosen from the integer 0, 1 or 2; (iv) unsubstituted, mono- or di- substituted C 4 -C 18 spirobicyclic amine; or (v) unsubstituted, mono- or di- substituted C 4 -C 18 spirotricyclic amine; said substituents for (iv) and (v) being independently chosen for each occurrence from aryl, C 1 -C 6 alkyl, C 1 - 6 alkoxy or phenyl(C 1 -C 6)alkyl; at the 11-position ring atom, said ring atoms being numbered according to the International Union of Pure and Applied Chemistry rules of nomenclature starting with the 1-position ring atom being the carbon atom para to the oxygen atom of the pyran ring and numbering clockwise therefrom, said photochromic material being free of spiro-substituents at the 13-position. - a nitrogen containing substituent selected from (i) -N(R 15)R 16, R 15 and R 16 each being independently chosen from C 1 -C 8 alkyl, C 1 -C 8 alkylaryl, C 3 -C 20 cycloalkyl, C 4 -C 20 bicycloalkyl, C 5 -C 20 tricycloalkyl or C 1 -C 20 alkoxyalkyl and said aryl group being phenyl or naphthyl; (ii) a nitrogen containing ring represented by the following graphic formula: wherein each Y being independently chosen for each occurrence from -CH 2 -, -CH(R 17)-, -C(R 17)(R 17)-, -CH(aryl)-, -C(aryl) 2 - or -C(R 17)(aryl)-; X being -Y-, -O-, -S-, -NH-, -N(R 17)- or -N(aryl)-; R 17 being C 1 -C 6 alkyl; said aryl group being phenyl or naphthyl, m being chosen from the integer 1, 2 or 3 and p being chosen from the integer 0, 1, 2 or 3; provided that when p is 0, X is Y; (iii) a group represented by one of the following graphic formulae: wherein each R 19, R 20 and R 21 being chosen independently for each occurrence in each formula from hydrogen, C 1 -C 5 alkyl, phenyl or naphthyl; or the groups R 19 and R 20 together form a ring of 5 to 8 carbon atoms; R 18 being chosen independently for each occurrence from C 1 -C 6 alkyl, C 1-6 alkoxy, fluoro or chloro and n being chosen from the integer 0, 1 or 2; (iv) unsubstituted, mono- or di- substituted C 4 -C 18 spirobicyclic amine; or (v) unsubstituted, mono- or di- substituted C 4 -C 18 spirotricyclic amine; said substituents for (iv) and (v) being independently chosen for each occurrence from aryl, C 1 -C 6 alkyl, C 1 - 6 alkoxy or phenyl(C 1 -C 6)alkyl; (i) -N(R 15)R 16, R 15 and R 16 each being independently chosen from C 1 -C 8 alkyl, C 1 -C 8 alkylaryl, C 3 -C 20 cycloalkyl, C 4 -C 20 bicycloalkyl, C 5 -C 20 tricycloalkyl or C 1 -C 20 alkoxyalkyl and said aryl group being phenyl or naphthyl; (ii) a nitrogen containing ring represented by the following graphic formula: wherein each Y being independently chosen for each occurrence from -CH 2 -, -CH(R 17)-, -C(R 17)(R 17)-, -CH(aryl)-, -C(aryl) 2 - or -C(R 17)(aryl)-; X being -Y-, -O-, -S-, -NH-, -N(R 17)- or -N(aryl)-; R 17 being C 1 -C 6 alkyl; said aryl group being phenyl or naphthyl, m being chosen from the integer 1, 2 or 3 and p being chosen from the integer 0, 1, 2 or 3; provided that when p is 0, X is Y; (iii) a group represented by one of the following graphic formulae: wherein each R 19, R 20 and R 21 being chosen independently for each occurrence in each formula from hydrogen, C 1 -C 5 alkyl, phenyl or naphthyl; or the groups R 19 and R 20 together form a ring of 5 to 8 carbon atoms; R 18 being chosen independently for each occurrence from C 1 -C 6 alkyl, C 1-6 alkoxy, fluoro or chloro and n being chosen from the integer 0, 1 or 2; (iv) unsubstituted, mono- or di- substituted C 4 -C 18 spirobicyclic amine; or (v) unsubstituted, mono- or di- substituted C 4 -C 18 spirotricyclic amine; said substituents for (iv) and (v) being independently chosen for each occurrence from aryl, C 1 -C 6 alkyl, C 1 - 6 alkoxy or phenyl(C 1 -C 6)alkyl;