A compound comprising a conjugate of a photosensitiser and chitosan, wherein said compound is a compound of Formula: wherein n is an integer greater than or equal to 10, preferably an integer from 10 to 100, R appears n times in said compound and in 0.5%-99.5% of said total Rn groups, each R is a group A selected from: H, wherein a is 1, 2, 3, 4 or 5; and X is Br, Cl or OH; wherein each R 1, which may be the same or different, is selected from H, CH 3 and -(CH 2) c -CH 3; b is 1, 2, 3, 4 or 5; and c is 0, 1, 2, 3, 4 or 5; wherein Y is O; S; SO 2; -NCH 3; or -N(CH 2) e CH 3; d=1, 2, 3, 4 or 5; and e=1, 2, 3, 4 or 5; wherein R 2 is -(CH 2) h -CH 3 or -CO-(CH 2) h -CH 3; f is 1, 2, 3, 4 or 5; g is 1, 2, 3, 4 or 5; and h is 0, 1, 2, 3, 4 or 5; wherein R 3 is -(CH 2) j -CH 3, i is an integer from 1 to 200, preferably from 1-10; j is 0, 1, 2, 3, 4 or 5; and k is 1, 2, 3, 4 or 5; wherein R 3 is -(CH 2) j -CH 3, i is an integer from 1 to 200, preferably from 1-10; and j is 0, 1, 2, 3, 4 or 5; wherein R 3 is -(CH 2) j -CH 3, i is an integer from 1 to 200, preferably from 1-10; j is 0, 1, 2, 3, 4 or 5; and each R 1, which may be the same or different, is selected from H, CH 3 and -(CH 2) c -CH 3; and c is 0, 1, 2, 3, 4 or 5; wherein R 3 = -(CH 2) j -CH 3, i is an integer from 1 to 200, preferably from 1-10; and j is 0, 1, 2, 3, 4 or 5; wherein R 3 = -(CH 2) j -CH 3, i is an integer from 1 to 200, preferably from 1-10; L is 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10; and j is 0, 1, 2, 3, 4 or 5; and wherein m is 1, 2, 3, 4 or 5; wherein each R group may be the same or different; and in 0.5%-99.5% of said total Rn groups, each R is a group B selected from: and wherein p is 0, 1, 2, 3, 4 or 5; q is 1, 2, 3, 4 or 5; and r is 1, 2, 3, 4 or 5; R 4 is a group selected from: and W is a group selected from O, S, NH or N(CH 3); R 5 is a group selected from: -(CH 2) s -CO-; -(CH 2) s -Z-(CH 2) t CO- and -(CH 2) s -Z-(CH 2) t -Z-CO-; wherein s is 0, 1, 2, 3, 4 or 5; t is 0, 1, 2, 3, 4 or 5; Z is NH, O, S, or SO 2; R 6 is a group selected from -CN and CH 3; R 7 is a group selected from: and V is a group selected from CO, SO 2, PO, PO 2 H or CH 2; and R 8 is a group (substituted in the o, m or p position), which may be the same or different, selected from H, -OH, -OCH 3, -CH 3, -COCH 3, C(CH 3) 4, -NH 2, -NHCH 3, -N(CH 3) 2 and -NCOCH 3; wherein each R group may be the same or different. n is an integer greater than or equal to 10, preferably an integer from 10 to 100, R appears n times in said compound and in 0.5%-99.5% of said total Rn groups, each R is a group A selected from: H, wherein a is 1, 2, 3, 4 or 5; and X is Br, Cl or OH; wherein each R 1, which may be the same or different, is selected from H, CH 3 and -(CH 2) c -CH 3; b is 1, 2, 3, 4 or 5; and c is 0, 1, 2, 3, 4 or 5; wherein Y is O; S; SO 2; -NCH 3; or -N(CH 2) e CH 3; d=1, 2, 3, 4 or 5; and e=1, 2, 3, 4 or 5; wherein R 2 is -(CH 2) h -CH 3 or -CO-(CH 2) h -CH 3; f is 1, 2, 3, 4 or 5; g is 1, 2, 3, 4 or 5; and h is 0, 1, 2, 3, 4 or 5; wherein R 3 is -(CH 2) j -CH 3, i is an integer from 1 to 200, preferably from 1-10; j is 0, 1, 2, 3, 4 or 5; and k is 1, 2, 3, 4 or 5; wherein R 3 is -(CH 2) j -CH 3, i is an integer from 1 to 200, preferably from 1-10; and j is 0, 1, 2, 3, 4 or 5; wherein R 3 is -(CH 2) j -CH 3, i is an integer from 1 to 200, preferably from 1-10; j is 0, 1, 2, 3, 4 or 5; and each R 1, which may be the same or different, is selected from H, CH 3 and -(CH 2) c -CH 3; and c is 0, 1, 2, 3, 4 or 5; wherein R 3 = -(CH 2) j -CH 3, i is an integer from 1 to 200, preferably from 1-10; and j is 0, 1, 2, 3, 4 or 5; wherein R 3 = -(CH 2) j -CH 3, i is an integer from 1 to 200, preferably from 1-10; L is 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10; and j is 0, 1, 2, 3, 4 or 5; and wherein m is 1, 2, 3, 4 or 5; wherein each R group may be the same or different; and in 0.5%-99.5% of said total Rn groups, each R is a group B selected from: and wherein p is 0, 1, 2, 3, 4 or 5; q is 1, 2, 3, 4 or 5; and r is 1, 2, 3, 4 or 5; R 4 is a group selected from: and W is a group selected from O, S, NH or N(CH 3); R 5 is a group selected from: -(CH 2) s -CO-; -(CH 2) s -Z-(CH 2) t CO- and -(CH 2) s -Z-(CH 2) t -Z-CO-; wherein s is 0, 1, 2, 3, 4 or 5; t is 0, 1, 2, 3, 4 or 5; Z is NH, O, S, or SO 2; R 6 is a group selected from -CN and CH 3; R 7 is a group selected from: and V is a group selected from CO, SO 2, PO, PO 2 H or CH 2; and R 8 is a group (substituted in the o, m or p position), which may be the same or different, selected from H, -OH, -OCH 3, -CH 3, -COCH 3, C(CH 3) 4, -NH 2, -NHCH 3, -N(CH 3) 2 and -NCOCH 3; wherein each R group may be the same or different.