Colorant compounds

A compound of the formula

• wherein R1, R2, R3, and R4 each, independently of the others, is (i) a hydrogen atom, (ii) an alkyl group, (iii) an aryl group, (iv) an arylalkyl group, or (v) an alkylaryl group, wherein R, and R2 can be joined together to form a ring, wherein R3 and R4 can be joined together to form a ring, and wherein R1, R2, R3, and R4 can each be joined to a phenyl ring in the central structure;
• wherein a and b each, independently of the others, is an integer which is 0, 1, 2, or 3;
• wherein R5 and R6 are each optionally present and wherein each of R5 and R6 independently of the other, if present, are independently selected from (i) an alkyl group, (ii) an aryl group, (iii) an arylalkyl group, (iv) an alkylaryl group, (v) a halogen atom, (vi) an ester group, (vii) an amide group, (viii) a sulfone group, (ix) an amine group or ammonium group, (x) a nitrile group, (xi) a nitro group, (xii) a hydroxy group, (xiii) a cyano group, (xiv) a pyridine or pyridinium group, (xv) an ether group, (xvi) an aldehyde group, (xvii) a ketone group, (xviii) a carbonyl group, (xix) a thiocarbonyl group, (xx) a sulfate group, (xxi) a sulfide group, (xxii) a sulfoxide group, (xxiii) a phosphine or phosphonium group, (xxiv) a phosphate group, (xxv) a mercapto group, (xxvi) a nitroso group, (xxvii) an acyl group, (xxviii) an acid anhydride group, (xxix) an azide group, (xxx) an azo group, (xxxi) a cyanato group, (xxxii) an isocyanato group, (xxxiii) a thiocyanato group, (xxxiv) an isothiocyanato group, (xxxv) a urethane group, or (xxxvi) a urea group, wherein R5 and R6 can each be joined to a phenyl ring in the central structure,
• wherein R8, R9, and R10 each, independently of the other, is optionally present and wherein each of R8, R9, and R10, if present, is independently selected from (i) a hydrogen atom, (ii) an alkyl group, (iii) an aryl group, (iv) an arylalkyl group, or (v) an alkylaryl group;
• wherein R″ is optionally present and wherein R′ and R″, if present, are each independently selected from (i) an alkyl group, (ii) an aryl group, (iii) an arylalkyl group, or (iv) an alkylaryl group;
• and
• wherein at least one of R′ or R″ contains at least about 5 carbon atoms.