Display element and method of driving the same

1. A display element comprising:

an electrochromic compound which is colored or decolored due to oxidation or reduction,

a metallic salt compound,

an electrolyte, and

white scattering material incorporated between opposed electrodes, wherein

the metallic salt compound causes a color variation by dissolution-deposition of a metal element; and

multi-color display of substantially 3 or more colors comprising black display, white display and colored display other than black are carried out by a driving operation of the opposite electrodes, wherein a coloring overvoltage (VECW) and the decoloring overvoltage (VECE) of an electrochromic dye, and the deposition overvoltage (VAgW) and the dissolution overvoltage (VAgE) of silver of a silver salt compound satisfy all the conditions defined by following Relational expression (X):

VECW absolute value>VECE absolute value

VECW absolute value>VAgE absolute value

VAgW absolute value>VECE absolute value

VAgW absolute value>VAgE absolute value.  Relational expression (X).

2. The display element of claim 1 , wherein the metallic salt compound comprises a compound containing silver salt.

3. The display element of claim 1 , wherein the electrochromic compound is colored due to oxidation and is decolored to be transparent due to reduction.

4. The display element of claim 1 , wherein the electrochromic compound is colored due to reduction and is decolored to be transparent due to oxidation.

5. The display element of claim 1 , wherein the electrochromic compound comprises a compound represented by Formula (A):

wherein R 1 represents a substituted or unsubstituted aryl group, R 2 and R 3 each represents a hydrogen atom or a substituent, X represents >N—R 4 , an oxygen atom or a sulfur atom, and R 4 represents a hydrogen atom or a substituent.

6. The display element of claim 1 , wherein the electrochromic compound comprises a compound represented by Formula (1) or Formula (2):

wherein R 1 and R 2 each represents a hydrogen atom, an aryl group or a heteroaryl group each having 14 or less carbon atoms; a branched alkylene group or an alkenylene group each having 10 or less carbon atoms; or a cycloalkylene group; n1 and m1 each represents an integer of 0 to 10; and X 1 − represents an ion which neutralizes the charge,

wherein R 3 represents: —(CH 2 ) m — wherein m represents an integer of 0 to 10; an arylene group or a heteroarylene group each having 14 or less carbon atoms, a branched alkylene group or an alkenylene group each having 10 or less carbon atoms or a cycloalkylene group; each of the arylene group, heteroarylene group, branched alkylene group, branched alkenylene group or cycloalkylene group may have a —P(O)(OH) 2 group through a —(CH 2 ) n — group or may be arbitrarily substituted, wherein n represents an integer of 0 to 10; R 4 represents a group represented by —(CH 2 ) p —R 5 wherein p represents an integer of 0 to 10 and R 5 represents —P(O)(OH) 2 group or an aryl group or a heteroaryl group each having 14 or less carbon atoms, and an alkyl group or an alkenyl group each having 10 or less carbon atoms or a cycloalkyl group or a hydrogen atom; and X 2 − represents an ion which neutralizes the charge.

7. The display element of claim 1 , wherein the electrochromic compound comprises a compound represented by Formula (I) to Formula (VI):

wherein R 1 and R 2 each represents a hydrogen atom or a substituent; R 3 and R 4 each represents a hydrogen atom or a substituent; m and p each represents an integer of 0 to 4; X represents an oxygen atom or a sulfur atom; and A − represents a counter ion to balance charge.

8. The display element of claim 1 , wherein the electrochromic compound comprises a compound represented by Formula [1] to Formula [8]:

wherein R 1 and R 2 each represents a substituent; R 3 represents a hydrogen atom or a substituent and when R 3 represents a hydrogen atom either R 1 or R 2 represents amino group; a and b each represents an integer of 0 to 5; when a and b each is 2 or more, 2 or more R 1 's or 2 or more R 2 's each may be the same or different; and adjacent R 1 's or R 2 's each may join to form a ring,

wherein R 4 and R 7 each represents a substituent; R 5 and R 6 each represents a alkyl group; R 5 and R 6 may join to form a ring or an ortho position of the phenyl group joining B and X2 may directly join to form a ring; X 1 represents —CR 30 R 31 —, —NR 32 , —O— or —S—; X 2 represents —O— or —S—; B represents ═CH— or ═N—; c represents an integer of 0 to 4 and when c is 2 or more, 2 or more R 4 's each may be the same or different or adjacent R 4 's may join to form a ring; d is an integer of 0 to 5, and when d is 2 or more, 2 or more R 7 's each may be the same or different or adjacent R 7 's may join to form a ring; and o represents 1 or 2,

wherein R 8 to R 11 each represents a hydrogen atom or a substituent; R 12 represents a substituent; X 3 and X 4 each represents —CR 30 , R 31 —, —NR 32 , —O— or —S—; e represents an integer of 0 to 4 and when e is 2 or more, 2 or more R 12 's each may be the same or different or adjacent R 12 's may join to form a ring; and n represents 0 or 1,

wherein R 18 represents a hydroxyl group, an alkoxy group or an amino group; R 19 and R 20 each represents a substituent; h is an integer of 0 to 4 and when h is 2 or more, 2 or more R 20 's each may be the same or different or adjacent R 20 's may join to form a ring; i is an integer of 0 to 5 and when i is 2 or more, 2 or more R 19 's each may be the same or different and adjacent R 19 's may join to form a ring, further adjacent R 19 and R 20 may join to form a ring; X 6 represents —O— or —NR 32 ; and Z represents a residual group needed to form an aromatic or heterocyclic ring,

wherein R 22 and R 23 each represent a substituent; k and l each independently represent an integer of 0 to 4; when k and l represent 2 or more, 2 or more R 22 's or 2 or more R 23 's may be the same or different, and further adjacent R 22 's or R 23 's may join to form a ring,

wherein R 24 represents a hydroxyl group, an alkoxy group, or an amino group; R 25 represents an aryl group or a heterocyclic group; R 26 represents a hydrogen atom, an alkyl group, an aryl group, a heterocyclic group, an acyl group, or a carbamoyl group; R 27 represents a substituent; m represents an integer of 0 to 4, when m represents 2 or more, 2 or more R 27 's each may be the same or different, and further adjacent R 27 's may join to form a ring,

wherein R 28 and R 29 each represent a substituent; n represents an integer of 0 to 4, when n represents 2 or more, 2 or more R 29 's each may be the same or different, and further adjacent R 29 's may join to form a ring; and Y represents an electron attractive group,

wherein R 30 and R 31 represent a hydrogen atom, a hydroxyl group, an alkoxy group, or an amino group; R 30 and R 31 do not represent a hydrogen atom simultaneously; R 32 and R 33 each represent a substituent; p and q each independently represent an integer of 0 to 4, when p and q are 2 or more, 2 or more R 32 's or 2 or more R 33 's each may be the same or different, adjacent R 32 's or R 33 's each may join to form a ring.

9. The display element of claim 1 , wherein the electrochromic compound is chemically or physically adsorbed on a surface of at least one of the opposite electrodes.

10. The display element of claim 1 , wherein the electrochromic compound comprises at least one of a absorption group containing —CO 2 H, —PO(OH) 2 , —OPO(OH) 2 , —SO 3 H or —Si(OR) 3 , wherein R represents a hydrogen atom or an alkyl group.

11. The display element of claim 1 , wherein at least one of the opposite electrodes comprises a metal oxide porous layer and the electrochromic compound is supported on the metal oxide porous layer.

12. The display element of claim 1 , wherein the white scattering material comprises TiO 2 , ZnO or Al 2 O 3 .

13. The display element of claim 1 , wherein substantially black state is displayed by a cathode reaction.

14. The display element of claim 1 , wherein a colored display other than black is conducted by a level arrangement of display areas which creates hues practically differing from one another.

15. The display element of claim 14 , wherein different electrochromic compounds are supported on the metal oxide porous layer.

16. The display element of claim 15 , wherein different electrochromic compounds are separately coated on the metal oxide porous layer by an ink jet method.

17. A method of driving the display element of claim 1 , wherein a voltage (VW) between the opposite electrodes during a white display driving operation satisfies all the conditions defined by following Relational expression (Y):

VECW absolute value>VW>VECE absolute value

VECW absolute value>VW>VAgE absolute value

VAgW absolute value>VW>VECE absolute value

VAgW absolute value>VW>VAgE absolute value,  Relational expression (Y)

wherein VECW, VECE, VAgE, and VAgW represents a coloring overvoltage and a decoloring overvoltage of an electrochromic dye, and a deposition overvoltage and a dissolution overvoltage of silver of a silver salt respectively.