Synthetically expedient water-dispersible IR dyes having improved lightfastness

1. 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 , a hydrophilic ligand andlor a ligand suitable for reducing cofacial interactions;

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 ); and

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;

W is a hydrophilic group, each W group being independently selected from a substituent comprising a sulfonic acid group (including salts thereof), or a substituent comprising a sulfonamide group;

n1 is 0, 1, 2 or 3;

n2 is 0, 1, 2 or 3;

n3 is 0, 1, 2 or 3;

n4 is 0, 1, 2 or 3;

provided that at least one of n1, n2, n3 or n4 is greater than 0.

2. The dye of claim 1 , wherein each W group is independently selected from a sulfonamide group, —SO 3 H or —SO 3 Z, wherein Z is Li, Na, K or N + (R m )(R n )(R s )(R t ) and wherein R m , R n , R s , R t may be the same or different and are independently selected from H, C 1-8 alkyl, C 6-12 arylalkyl or C 6-12 aryl.

3. The dye of claim 2 , wherein the sulfonamide group is of formula —SO 2 NR p R q , wherein R p and R q are independently selected from H, C 1-8 alkyl, C 6-12 arylalkyl, C 6-12 aryl or —(CH 2 CH 2 O) e R e , wherein e is an integer from 2 to 5000 and R e is H, C 1-8 alkyl or C(O)C 1-8 alkyl.

4. The dye of claim 1 , wherein R 1 and R 2 are both H.

5. The dye of claim 1 , wherein R 1 and R 2 are both C 1-8 alkoxy.

6. The dye of claim 1 , wherein M is Ga(OH), Ga(Cl), Ga(OC(O)R 4 ), Ga(OR 3 ) or Ga(OW), wherein W is as defined in any one of claims 1 , 3 or 4 .

7. The dye of claim 1 , wherein M is Ga(OH).

8. The dye of claim 6 , wherein A 1 is a ligand of formula (IIIa):

wherein:

C 1 represents a core unit having two or more branching positions;

each P 1 is independently selected from H, a hydrophilic moiety or a branched moiety;

g 1 is an integer from 2 to 8;

q 1 is 0 or an integer from 1 to 6; and

each p 1 is independently selected from 0 or an integer from 1 to 6.

9. The dye of claim 8 , wherein C 1 is a C atom, an N atom, a Si atom, a C 1-8 alkyl residue, a C 3-8 cycloalkyl residue, or a phenyl residue.

10. The dye of claim 8 , wherein g is 2, 3 or 4.

11. The dye of claim 8 , wherein A 1 is a pentaerythritol derivative, a triethanolamine derivative, a phloroglucinol derivative, or a 3,5-dihydroxybenzyl alcohol derivative.