Gallium naphthalocyanine salts for use as improved infrared dyes
There is provided an IR-absorbing naphthalocyanine dye of formula (I): wherein M is Ga(A 1 ); A 1 is an axial ligand selected from —OH, halogen, —OR 3 , —OC(O)R 4 or —O(CH 2 CH 2 O) e R e wherein e is an integer from 2 to 10 and R e is H, C 1-8 alkyl or C(O)C 1-8 alkyl; R 1 and R 2 may be the same or different and are selected from hydrogen or C 1-12 alkoxy; R 3 is selected from C 1-12 alkyl, C 5-12 aryl, C 5-12 arylalkyl or Si(R x )(R y )(R z ); R 4 is selected from C 1-12 alkyl, C 5-12 aryl or C 5-12 arylalkyl; R x , R y and R z may be the same or different and are selected from C 1-12 alkyl, C 5-12 aryl, C 5-12 arylalkyl, C 1-12 alkoxy, C 5-12 aryloxy or C 5-12 arylalkoxy; and each B is independently selected from a base, wherein BH + has a pK a of between 4 and 9. The dye is suitable for use in IR-absorbing inkjet inks, providing compatibility with known CMYK inks together with an optimally red-shifted λ max .
1. An IR-absorbing naphthalocyanine dye of formula (I):
wherein
M is Ga(A 1 );
A 1 is an axial ligand selected from the group consisting of: —OH, halogen, —OR 3 , —OC(O)R 4 and —O(CH 2 CH 2 O) e R e wherein e is an integer from 2 to 10 and R e is H, C 1-8 alkyl or C(O)C 1-8 alkyl;
R 1 and R 2 may be the same or different and are selected from the group consisting of: hydrogen and C 1-12 alkoxy;
R 3 is selected from the group consisting of: C 1-12 alkyl, C 5-12 aryl, C 5-12 arylalkyl and Si(R x )(R y )(R z );
R 4 is selected from the group consisting of: C 1-12 alkyl, C 5-12 aryl and C 5-12 arylalkyl;
R x , R y and R z may be the same or different and are selected from the group consisting of: C 1-12 alkyl, C 5-12 aryl, C 5-12 arylalkyl, C 1-12 alkoxy, C 5-12 aryloxy and C 5-12 arylalkoxy; and
each B is independently a base, wherein BH + has a pK a of between 4 and 9.
2. The dye of claim 1 , wherein BH + has a pK a of between 4.5 and 8.
3. The dye of claim 1 , wherein each B is independently selected from the group consisting of a nitrogen base and an oxyanion base.
4. The dye of claim 3 , wherein said nitrogen base is a nitrogen-containing C 5-12 heteroaryl base.
5. The dye of claim 4 , said nitrogen base is imidazole or pyridine.
6. The dye of claim 3 , wherein said oxyanion base is a carboxylate base.
7. The dye of claim 6 , wherein said carboxylate base is of formula R 5 C(O)O — , wherein R 5 is selected from the group consisting of: C 1-12 alkyl, C 5-12 aryl and C 5-12 arylalkyl.
8. The dye of claim 1 , wherein each B is the same.
9. The dye of claim 1 , wherein each B is imidazole.
10. The dye of claim 1 , wherein R 1 and R 2 are both H.
11. The dye of claim 1 , wherein M is Ga(OH).
12. An inkjet ink comprising a dye according to claim 1 .
13. An inkjet ink comprising a dye according to claim 1 , wherein said ink has a pH in the range of 4 to 7.