Azo compound, ink containing azo compound, and display and electronic paper containing the ink

1. An ink, comprising:

a solvent having a relative permittivity at 22° C. and at a measurement frequency of 1 kHz of 3 or less and having a solubility in water at 25° C. of 20 mg/L or less; and

an azo compound represented by formula (1):

wherein:

R 1 and R 2 each independently represent a hydrocarbon group optionally having a substituent, wherein at least one of R 1 and R 2 is a branched alkyl group having from 6 to 20 carbon atoms; and

X 1 , X 11 and A 1 each independently represent a hydrogen atom or a substituent.

2. The ink of claim 1 , wherein the solvent comprises at least one solvent selected from a group consisting of a hydrocarbon solvent, a silicone oil and a fluorocarbon solvent.

3. The ink of claim 1 , wherein a product εC of a molar absorbance coefficient ε(L·mol −1 ·cm −1 ) at absorption maximum wavelength of an n-decane solution of the azo compound, and a saturation solubility C (mol·L −1 ) of the solution at 5° C. is 1000 cm −1 or more.

4. The ink of claim 1 , further comprising:

at least one compound selected from a group consisting of a heterocyclic compound, a cyanovinyl compound and an anthraquinone compound.

5. The ink of claim 4 , wherein the heterocyclic compound is at least one compound selected from a group consisting of formulae (2) to (5):

wherein:

R 101 and R 102 each independently represent a hydrogen atom or an arbitrary substituent:

D 3 and D 4 each independently represent an arbitrary substituent,

e represents an integer of from 0 to 5, and when e is 2 or more, 2 or more D 3 s existing in one molecule may be the same or different;

g represents an integer of from 0 to 4, and when g is 2 or more, 2 or more D 4 s existing in one molecule may be the same or different,

wherein:

R 201 to R 208 each independently represent a hydrogen atom or a substituent;

Z represents a nitrogen atom or a methine group optionally having a substituent,

wherein:

R 301 , R 302 , D 5 and D 6 each independently represent a substituent;

l represents an integer of from 0 to 4, and when l is 2 or more, 2 or more D 5 s existing in one molecule may be the same or different;

j represents an integer of from 0 to 4, and when j is 2 or more, 2 or more D 6 s existing in one molecule may be the same or different, and

wherein:

R 601 , R 602 , D 9 and D 10 each independently represent a substituent;

A 3 represents a hydrogen atom or a substituent;

p represents an integer of from 0 to 5, and when p is 2 or more, 2 or more D 9 s existing in one molecule may be the same or different;

q represents an integer of from 0 to 4, and when q is 2 or more, 2 or more D 10 s existing in one molecule may be the same or different;

X 3 represents a nitrogen atom, or a methine group having a halogen atom, a cyano group or a group —COOR 605 as a substituent;

R 605 represents a hydrogen atom, an alkyl group having a carbon number of from 1 to 20 and optionally having a substituent, an aryl group having a carbon number of from 6 to 20 and optionally having a substituent, or a heteroaryl group having a carbon number of from 2 to 20 and optionally having a substituent.

6. The ink of claim 4 , comprising an anthraquinone compound represented by formula (7):

wherein:

D 8 represents a substituent;

t represents an integer of from 0 to 8, and when t is 2 or more, 2 or more D 8 s existing in one molecule may be the same or different.

7. The ink of claim 1 , which is adapted to function in displays or optical shutters.

8. A display, comprising a display area comprising the ink of claim 1 , and which displays an image by controlling a voltage application to the display area.

9. The display of claim 8 , wherein the display area further comprises at least either one of electrophoretic particles and an aqueous medium.

10. The display of claim 8 , which displays an image by changing the coloration state through control of voltage application.

11. The display of claim 8 , which displays an image according to an electrowetting system or an electrophoretic system.

12. An electronic paper, comprising the display of claim 8 .

13. An azo compound represented by formula (8):

wherein:

R 3 and R 4 each independently represent an alkyl group having a carbon number of from 1 to 20 and optionally having a substituent, wherein at least one of R 3 and R 4 is a branched alkyl group having from 6 to 20 carbon atoms;

R 5 represents an alkyl group having a branched chain and having a carbon number of from 4 to 20 and optionally having a substituent;

X 2 and X 12 each independently represent a hydrogen atom or a substituent.

14. The ink of claim 1 , wherein R 1 and R 2 are each independently a branched alkyl group having from 6 to 20 carbon atoms, X 11 is hydrogen, and X 1 is an acylamino group having from 1 to 20 carbon atoms and optionally having a branched chain and a cyclic structure.

15. The azo compound of claim 13 , wherein R 3 and R 4 are each independently a branched alkyl group having from 6 to 20 carbon atoms, X 12 is hydrogen, and X 2 is an acylamino group having from 1 to 20 carbon atoms and optionally having a branched chain and a cyclic structure.