The invention relates to cationic direct dyes of the formula I (1), wherein m and n are independently from each other 0 or 1, D is an aromatic or a cationic heteroaromatic group, which are further specified, K is an aromatic or heteroaromatic group, E.sub.1 and E.sub.2 are independently from each other CH or N, An is an anion and a is a number from 1 to 6 and R.sub.1 and R.sub.2 are independently from each other and further specified. The compounds show washfastness at hair-dying. ##STR00001##

The invention relates to cationic direct dyes of the formula I (1), wherein m and n are independently from each other 0 or 1, D is an aromatic or a cationic heteroaromatic group, which are further specified, K is an aromatic or heteroaromatic group, E.sub.1 and E.sub.2 are independently from each other CH or N, An is an anion and a is a number from 1 to 6 and R.sub.1 and R.sub.2 are independently from each other and further specified. The compounds show washfastness at hair-dying.

##STR00001##

Described herein is a method of dyeing the hair. The method includes applying to the hair a hair color composition including one or more direct dye compounds and rinsing the hair with water. The one or more direct dye compounds each include a yellow chromophore, one or two permanent cations, one to four incipient cations, and one or more hydrophobic moieties. The incipient cations are pendant to the core structure and are neutral. The one or more direct dye compounds enter the hair shaft after the hair color composition is applied to the hair. The hair color composition has a pH of from about 7 to about 11. The pH of the hair after rinsing is from about 3.5 to about 6. The rinsing of the hair causes one or more of the one to four incipient cations to change from neutral to positively charged inside of the hair shaft.

Described herein is a method of dyeing the hair. The method includes applying to the hair a hair color composition including one or more direct dye compounds and rinsing the hair with water. The one or more direct dye compounds each include a yellow chromophore, one or two permanent cations, one to four incipient cations, and one or more hydrophobic moieties. The incipient cations are pendant to the core structure and are neutral. The one or more direct dye compounds enter the hair shaft after the hair color composition is applied to the hair. The hair color composition has a pH of from about 7 to about 11. The pH of the hair after rinsing is from about 3.5 to about 6. The rinsing of the hair causes one or more of the one to four incipient cations to change from neutral to positively charged inside of the hair shaft.

Provided are a compound that generates an SHG signal but has suppressed generation of a TPF signal. Also provided is a cell examination method using the same. A compound for generating a second harmonic of light, the compound being an azobenzene derivative of formula (1), or a salt thereof. (R1 and R2 independently represent alkyl groups having 6-12 carbon atoms, and R3 to R18 independently represent substituents selected from hydrogen, halogens, alkyl groups, alkoxy groups, aryl groups, amino groups, hydroxyl groups, nitro groups, and cyano groups, but R5 and R6, R9 and R10, R13 and R14, and R17 and R18 may combine together and form a ring structure having 5-7 carbon atoms. X represents N+R19R20R21, a sulfonyl group, a carboxyl group, or an OR group. Here, R19, R20, and R21 independently represent straight-chain or branched alkyl groups having 1-5 carbon atoms, and OR represents a monovalent polyalkylene oxide group terminated by an alkoxy group. a is 0 or 1, b is 0 or 1, and n is an integer of 1-10.)