Compound of the following formula I wherein: • n represents 0 or 1, • represents a single bond or no bond, • represents a single or a double bond, • R 1 and R' 1 represent independently from each other: - H, - a linear or branched (C 1 -C 18)-alkyl, - a (C 3 -C 8)-cycloalkyl, - - -NR 3 +, R representing: - H, - a linear or branched (C 1 -C 18)-alkyl, - a (C 3 -C 8)-cycloalkyl, • R 2, R 3, R 4 and R 5 represent independently from each other: - H, - a linear or branched (C 1 -C 18)-alkyl, - a (C 3 -C 8)-cycloalkyl, - - -NR 3 +, R representing: - H, - a linear or branched (C 1 -C 18)-alkyl, - a (C 3 -C 8)-cycloalkyl, • X represents one or more physiologically acceptable counter anion(s), providing that: - at least one of R 1, R' 1, R 2, R 3, R 4 and R 5 represents one of the following groups: ∘ or o -NR 3 +, - n, and the bonds 1 to 7 are such as: ∘ n=0, represents a single bond, bonds 1, 4 and 6 represent a double bond, and bonds 2, 3, 5 and 7 represent a single bond, or ∘ n=0, ------- represents no bond, bonds 1, 3, 5 and 7 represent a double bond, and bonds 2, 4 and 6 represent a single bond, or ∘ n=1, ------- represents no bond, bonds 2, 5 and 7 represent a double bond, and bonds 1, 3, 4 and 6 represent a single bond, for use in the treatment of pathologies sensitive to singlet oxygen, in particular for use in phototherapy and/or in the treatments of cancers. • n represents 0 or 1, • represents a single bond or no bond, • represents a single or a double bond, • R 1 and R' 1 represent independently from each other: - H, - a linear or branched (C 1 -C 18)-alkyl, - a (C 3 -C 8)-cycloalkyl, - - -NR 3 +, R representing: - H, - a linear or branched (C 1 -C 18)-alkyl, - a (C 3 -C 8)-cycloalkyl, - H, - a linear or branched (C 1 -C 18)-alkyl, - a (C 3 -C 8)-cycloalkyl, - - -NR 3 +, - H, - a linear or branched (C 1 -C 18)-alkyl, - a (C 3 -C 8)-cycloalkyl, • R 2, R 3, R 4 and R 5 represent independently from each other: - H, - a linear or branched (C 1 -C 18)-alkyl, - a (C 3 -C 8)-cycloalkyl, - - -NR 3 +, R representing: - H, - a linear or branched (C 1 -C 18)-alkyl, - a (C 3 -C 8)-cycloalkyl, - H, - a linear or branched (C 1 -C 18)-alkyl, - a (C 3 -C 8)-cycloalkyl, - - -NR 3 +, - H, - a linear or branched (C 1 -C 18)-alkyl, - a (C 3 -C 8)-cycloalkyl, • X represents one or more physiologically acceptable counter anion(s), providing that: - at least one of R 1, R' 1, R 2, R 3, R 4 and R 5 represents one of the following groups: ∘ or o -NR 3 +, - n, and the bonds 1 to 7 are such as: ∘ n=0, represents a single bond, bonds 1, 4 and 6 represent a double bond, and bonds 2, 3, 5 and 7 represent a single bond, or ∘ n=0, ------- represents no bond, bonds 1, 3, 5 and 7 represent a double bond, and bonds 2, 4 and 6 represent a single bond, or ∘ n=1, ------- represents no bond, bonds 2, 5 and 7 represent a double bond, and bonds 1, 3, 4 and 6 represent a single bond, for use in the treatment of pathologies sensitive to singlet oxygen, in particular for use in phototherapy and/or in the treatments of cancers. - at least one of R 1, R' 1, R 2, R 3, R 4 and R 5 represents one of the following groups: ∘ or o -NR 3 +, ∘ or o -NR 3 +, - n, and the bonds 1 to 7 are such as: ∘ n=0, represents a single bond, bonds 1, 4 and 6 represent a double bond, and bonds 2, 3, 5 and 7 represent a single bond, or ∘ n=0, ------- represents no bond, bonds 1, 3, 5 and 7 represent a double bond, and bonds 2, 4 and 6 represent a single bond, or ∘ n=1, ------- represents no bond, bonds 2, 5 and 7 represent a double bond, and bonds 1, 3, 4 and 6 represent a single bond, ∘ n=0, represents a single bond, bonds 1, 4 and 6 represent a double bond, and bonds 2, 3, 5 and 7 represent a single bond, or ∘ n=0, ------- represents no bond, bonds 1, 3, 5 and 7 represent a double bond, and bonds 2, 4 and 6 represent a single bond, or ∘ n=1, ------- represents no bond, bonds 2, 5 and 7 represent a double bond, and bonds 1, 3, 4 and 6 represent a single bond,