Electrochromic system

• US 6,241,916 B1
• Filed: 01/12/1999
• Issued: 06/05/2001
• Est. Priority Date: 02/15/1996
• Status: Expired due to Fees

• Current Assignee: Bayer AG
• Original Assignee: Bayer AG
• Inventors: Haarer, Dietrich, Claussen, Uwe, Berneth, Horst, Simmerer, Jürgen, Schaller, Jochen
• Primary Examiner(s): WU, SHEAN CHIU
• Application Number:
  US09/125,198
• Time in Patent Office: 875 Days
• Field of Search: 252/583, 359/265, 359/267, 359/272, 359/276, 345/49
• US Class Current: 252/583
• CPC Class Codes: C07D 417/14 containing three or more hetero rings
• CPC Class Codes: C09K 9/02 Organic tenebrescent materials
• CPC Class Codes: G02F 1/1503 caused by oxidation-reduction reactions in organic liquid solutions, e.g. viologen solutions
• CPC Class Codes: G02F 2001/1502 complementary cell
• CPC Class Codes: G02F 2001/15145 the electrochromic layer comprises a mixture of anodic and cathodic compounds

Abstract

The novel electrochromic system comprises at least one reducible and at least one oxidizable substance OX₂ and RED₁ respectively, which are linked with one another via a bridge member, and is outstandingly suitable for use in an electrochromic device.

Claims

1. An electrochromic system comprising at least one oxidizable substance RED₁ and at least one reducible substance OX₂ which, by electron donation of the former at an anode and by electron acceptance of the latter at a cathode, in each case with an increase in the extinction in the visible range of the spectrum, are converted from a slightly colored or colorless form into a colored form OX₁ and RED₂ respectively, in each case the slightly colored or colorless form being reformed after charge compensation, wherein at least one of the substances RED₁ and OX₂ contained therein are linked together covalently via a bridge.

2. An electrochromic system as claimed in claim 1, which comprises at least one electrochromic substance of the formula (I)

in which

Y and Z independently of one another represent a radical OX₂ or RED₁, but in which at least one Y represents OX₂ and at least one Z represents RED₁,

in which

OX₂ represents the radical of a reversibly electrochemically reducible redox system and

RED₁ represents the radical of a reversibly electrochemically oxidizable redox system,

B represents a bridge member,

c represents an integer from 0 to 5 and

a and b independently of one another represent an integer from 0 to 5.

3. An electrochromic system as claimed in claim 2, which comprises at least one electrochromic substance of the formula (I) in which Y represents OX₂ and Z represents RED₁ and Y and Z alternate in their sequence.

4. An electrochromic system as claimed in claim 1, which comprises at least one electrochromic substance of the formulae

in which

B represents a bridge member, and

d represents an integer from 1 to 5.

5. An electrochromic system as claimed in claim 4, which comprises at least one electrochromic substance of the formulae (Ia)-(Id),

in which

OX₂ represents the radical of a cathodically reducible substance which, in the cyclic voltammogram recorded in an inert solvent at room temperature, shows at least two chemically reversible reduction waves, the first of these reduction waves leading to an increase in the extinction at not less than one wavelength in the visible range of the electromagnetic spectrum,

RED₁ represents the radical of the anodically reversibly oxidizable substance which, in the cyclic voltammogram recorded in an inert solvent at room temperature, shows at least two chemically reversible oxidation waves, the first of these oxidation waves leading to an increase in the extinction at not less than one wavelength in the visible range of the electromagnetic spectrum and

B represents a bridge member.

6. An electrochromic system as claimed in claim 4, which comprises at least one substance of the formula (Ia)-(Id), in which

OX₂ represents a radical of the formulae

in which

R² to R⁵, R⁸, R⁹ and R¹⁶ to R¹⁹ independently of one another denote C₁- to C₁₈-alkyl, C₂- to C₁₂-alkenyl, C₃- to C₇-cycloalkyl, C₇- to C₁₅-aralkyl or C₆- to C₁₀-aryl or

R⁴ and R⁵ or R⁸ and R⁹ together form a —

(CH₂)₂—

or —

(CH₃)—

bridge,

R⁶, R⁷ and R²² to R²⁵ independently of one another denote hydrogen, C₁- to C₄-alkyl, C₁- to C₄-alkoxy, halogen, cyano, nitro or C₁- to C₄-alkoxycarbonyl or

R²² and R²³ and/or R²⁴ and R²⁵ form a —

CH═

CH—

CH═

CH—

bridge,

R¹⁰ and R¹¹;

R¹² and R¹³; and

R¹⁴ and R¹⁵ independently of one another denote hydrogen or, in pairs, a —

(CH₂)₂—

, —

(CH₂)₃—

or —

CH═

CH—

bridge,

R⁶⁹ to R⁷⁴ independently of one another denote hydrogen or C₁-C₆-alkyl, or

R⁶⁹;

R¹² and/or R⁷⁰; and

R¹³ form a —

CH═

CH—

CH═

CH—

bridge,

R²⁰ and R²¹ independently of one another denote O, N—

CN, C(CN)₂ or N—

C₆- to C₁₀-aryl,

R²⁶ denotes hydrogen, C₁- to C₄-alkyl, C₁- to C₄-alkoxy, halogen, cyano, nitro, C₁- to C₄-alkoxycarbonyl or C₆- to C₁₀-aryl,

E¹ and E² independently of one another denote O, S, NR¹ or C(CH₃)₂ or

E¹ and E² together form a —

N—

(CH₂)₂—

N—

bridge,

R¹ denotes C₁- to C₁₈-alkyl, C₂- to C₁₂-alkenyl, C₄- to C₇-cycloalkyl, C₇- to C₁₅-aralkyl or C₆- to C₁₀-aryl,

Z¹ denotes a direct bond —

CH═

CH—

, —

C(CH₃)═

CH—

, —

C(CN)═

CH—

, —

CCl═

CCl—

, —

C(OH)═

CH—

, —

CCl═

CH—

, —

C≡

C—

, —

CH═

N—

N═

CH—

, —

C(CH₃)═

N—

N═

C(CH₃)—

or —

CCl═

N—

N═

CCl—

,

Z² denotes —

(CH₂)_r—

or —

CH₂—

C₆H₄—

CH₂—

,

r denotes an integer from 1 to 10,

X⁻

denotes an anion which is redox-inert under the conditions,

wherein bonding to the bridge member B is effected via one of the radicals R²-R¹⁹, R²-R²⁷ or, in the case where E¹ or E² represents NR¹, via R¹ and the radicals mentioned then represent a direct bond,

RED₁ represents one of the following radicals

wherein

R²⁸ to R³¹, R³⁴, R³⁵, R³⁸, R³⁹, R⁴⁶, R⁵³ and R⁵⁴ independently of one another denote C₁- to C₁₈-alkyl, C₂- to C₁₂-alkenyl, C₃- to C₇-cycloalkyl, C₇- to C₁₅-aralkyl or C₆- to C₁₀-aryl, and R⁴⁶, R⁵³ and R⁵⁴ additionally denote hydrogen,

R³², R³³, R³⁶, R³⁷, R⁴⁰, R⁴¹, R⁴² to R⁴⁵, R⁴⁷, R⁴⁸, R⁴⁹ to R⁵² and R⁵⁵ to R⁵⁷ independently of one another denote hydrogen, C₁- to C₄-alkyl, C₁- to C₄-alkoxy, halogen, cyano, nitro, C₁- to C₄-alkoxycarbonyl or C₆- to C₁₀-aryl and R⁵⁷ and R⁵⁸ additionally denote an optionally benzo-fused aromatic or quasiaromatic five- or six-membered heterocyclic ring and R⁴⁸ additionally denotes NR⁷⁵R⁷⁶,

R⁴⁹ and R⁵⁰ and/or R⁵¹ and R⁵² form a —

(CH₂)₃—

, —

(CH₂)₄—

, —

(CH₂)₅—

or —

CH═

CH—

CH═

CH—

bridge,

Z³ denotes a direct bond or a —

CH═

CH—

or —

N═

N—

bridge,

═

Z⁴═

denotes a direct double bond or a ═

CH—

CH═

or ═

N—

N═

bridge

E³ to E⁵, E¹⁰ and E¹¹ independently of one another denote O, S, NR⁵⁹ or C(CH₃)₂ and E⁵ additionally denotes C═

O or SO₂, or

E³ and E⁴ independently of one another denote —

CH═

CH—

,

E⁶ to E⁹ independently of one another denote S, Se or NR⁵⁹,

R⁵⁹, R⁷⁵ and R⁷⁶ independently of one another denote C₁- to C₁₂-alkyl, C₂- to C₈-alkenyl, C₃ to C₇-cycloalkyl, C₇- to C₁₅-aralkyl or C₆- to C₁₀-aryl and R⁷³ additionally denotes hydrogen, or

R⁷³ and R⁷⁵ in the meaning of NR⁷³R⁷⁴, together with the N atom to which they are bonded, form a five- or six-membered saturated ring which can contain further heteroatoms,

R⁶¹ to R⁶⁸ independently of one another denote hydrogen, C₁- to C₆-alkyl, C₁- to C₄-alkoxy, cyano, C₁- to C₄-alkoxycarbonyl or C₆- to C₁₀-aryl, or

R⁶¹;

R⁶² and R⁶⁷; and

R⁶⁸ independently of one another together form a —

(CH₂)₃—

, —

(CH₂)₄—

or —

CH═

CH—

CH═

CH—

bridge,

v denotes an integer between 0 and 10,

wherein bonding to the bridge member B is effected by one of the radicals R²-R⁵⁸, R⁶¹, R⁶², R⁶⁷, R⁶⁸ or, in the case where one of the radicals E³-E¹¹ represents NR⁵⁹, via R⁵⁹ and the radicals mentioned then represent a direct bond, and

B represents a bridge member of the formula —

(CH₂)_n—

or —

[Y¹_s(CH₂)_m—

Y²]_o—

(CH₂)_p—

Y³_q—

, each of which is optionally substituted by C₁- to C₄-alkoxy, halogen or phenyl,

Y¹ to Y³ independently of one another represent O, S, NR⁶⁰, COO, CONH, NHCONH, cyclopentanediyl, cyclohexanediyl, phenylene or naphthylene,

R⁶⁰ denotes C₁- to C₆-alkyl, C₂- to C₆-alkenyl, C₄- to C₇-cycloalkyl, C₇- to C₁₅-aralkyl or C₆- to C₁₀-aryl,

n denotes an integer from 1 to 12,

m and p independently of one another denote an integer from 0 to 8,

o denotes an integer from 0 to 6 and

q and s independently of one another denote 0 or 1.

7. An electrochromic system as claimed in claim 6, which comprises at least one substance of the formula (Ia)-(Id)

in which

O X₂ represents a radical of the formulae (II), (III), (IV) or (V),

in which

R², R³, R⁴, R⁵, R⁸ and R⁹ independently of one another represent C₁- to C₁₂-alkyl, C₂- to C₈-alkenyl, C₅- to C₇- cycloalllyl, C₇- to C₁₅-aralkyl or C₆- to C₁₀-aryl,

R⁶ and R⁷ independently of one another represent hydrogen, methyl, ethyl, methoxy, ethoxy, fluorine, chlorine, bromine, cyano, nitro, methoxycarbonyl or ethoxycarbonyl,

R¹⁰, R¹¹;

R¹², R¹³ and R¹⁴, R¹⁵ independently of one another represent hydrogen or, if Z¹ denotes a direct bond, in each case together in pairs represent a —

(CH₂)₂—

, —

(CH₂)₃—

or —

CH═

CH—

bridge,

or

R⁴, R⁵ and R⁸, R⁹ independently of one another in pairs together represent a —

(CH₂)₂—

or —

(CH₃)₃—

bridge, if Z¹ denotes a direct bond,

R⁶⁹ to R⁷⁴ independently of one another denote hydrogen or C₁-C₄-alkyl,

E¹ and E² are identical and represent O, S, NR¹ or C(CH₃)₂ or together form a —

N—

(CH₂)₂—

N—

bridge,

R¹ represents C₁- to C₁₂-alkyl, C₂- to C₄-alkenyl, C₅- to C₇-cycloalkyl, C₇- to C₁₅-aralkyl or C₆- to C₁₀-aryl,

Z¹ represents a direct bond, —

CH═

CH—

, —

C(CH₃)═

CH—

, —

C(CN)═

CH—

, —

C≡

C—

or —

CH═

N—

N═

CH—

,

Z² represents —

(CH)_r—

or —

CH₂—

C₆H₄—

CH₂—

,

r represents an integer between 1 and 6,

X⁻

represents a colorless anion which is redox-inert under the conditions,

wherein bonding to the bridge member B is effected by one of the radicals R²-R¹¹ or, in the case where E¹ or E² represents NR¹, via R¹ and the radicals mentioned then represent a direct bond,

RED₁ represents a radical of the formulae (X), (XI), (XII), (XIII), (XVI), (XVII), (XVIII) or (XX),

in which

R²⁸ to R³¹, R³⁴, R³⁵, R³⁸, R³⁹, R⁴⁶, R⁵³ and R⁵⁴ independently of one another denote C₁- to C₁₂-alkyl, C₂- to C₈-alkenyl, C₅- to C₇-cycloalkyl, C₇- to C₁₅-aralkyl or C₆- to C₁₀-aryl and

R⁴⁶, R⁵³ and R⁵⁴ additionally denote hydrogen,

R³², R³³, R³⁶, R³⁷, R⁴⁰, R⁴¹, R⁴⁷ to R⁵², R⁵⁵ and R⁵⁶ independently of one another denote hydrogen, methyl, ethyl, methoxy, ethoxy, fluorine, chlorine, bromine, cyano, nitro, methoxycarbonyl, ethoxycarbonyl or phenyl and

R⁵⁷ and R⁵⁸ additionally denote 2- or 4-pyridyl and

R⁴⁸ additionally denotes NR⁷⁵R⁷⁶,

Z³ denotes a direct bond or a —

CH═

CH—

or 13 N═

N—

bridge,

═

Z⁴═

denotes a direct bond or a ═

CH—

CH═

or ═

N—

N═

bridge,

E³ to E⁵, E¹⁰ and E¹¹ independently of one another denote O, S, NR⁵⁹ or C(CH₃)₂, but E³ and E⁴ have the same meaning,

E⁶ to E⁹ are identical to one another and denote S, Se or NR⁵⁹ and

E⁵ additionally denotes C═

O,

E⁶ represents NR⁵⁹, in which R⁵⁹ denotes a direct bond to the bridge B and

E⁷ to E⁹ have the abovementioned meaning but must not be identical to one another,

R⁵⁹, R⁷⁵ and R⁷⁶ independently of one another denote C₁- to C₁₂-alkyl, C₂- to C₈-alkenyl, C₅- to C₇-cycloalkyl, C₇- to C₁₅-aralkyl or C₆- to C₁₀-aryl, and R⁷³ additionally denotes hydrogen or

R⁷³ and R⁷⁴ in the meaning NR⁷³R⁷⁴, together with the N atom to which they are bonded, denote pyrrolidino, piperidino or morpholino,

R⁶¹, R⁶² and R⁶⁷, R⁶⁸ independently of one another represent hydrogen, C₁- to C₄-alkyl, methoxycarbonyl, ethoxycarbonyl or phenyl or in pairs together represent a —

(CH₂)₃—

or —

(CH₂)₄—

bridge,

R⁶³ to R⁶⁶ represents hydrogen and

v represents an integer from 1 to 6,

wherein bonding to the bridge member B is effected by one of the radicals R²⁸-R⁴¹, R⁴⁶-R⁵⁶, R⁶¹, R⁶², R⁶⁷, R⁶⁸ or, in the case where one of the radicals E³-E¹¹ represents NR⁵⁹, via R⁵⁹ and the radicals mentioned then represent a direct bond,

B represents a bridge member of the formulae —

(CH₂)_n—

, —

(CH₂)_m—

O—

(CH₂)_p—

, —

(CH)_m—

NR⁶⁰—

(CH₂)_p—

, —

(CH₂)_m—

C₆H₄—

(CH₂)_p—

, —

[O—

(CH₂)_p]_o—

O—

, —

[NR⁶⁰—

(CH₂)_p]_o—

NR⁶⁰—

, —

[C₆H₄—

(CH₂)_p]_o—

C₆H₄—

, —

(CH₂)_m—

OCO—

C₆H₄—

COO—

(CH₂)_p—

, —

(CH₂)_m—

NHCO—

C₆H₄—

CONH—

(CH₂)_p—

, —

(CH₂)_m—

NHCONH—

C₆H₄—

NHCONH—

(CH₂)_p—

, —

(CH₂)_m—

OCO—

(CH₂)_t—

COO—

(CH₂)—

, —

(CH₂)_mNHCO—

(CH₂)_t—

CONH—

(CH)_p—

, —

(CH₂)_m—

NHCONH—

(CH₂)_t—

NHCONH—

(CH₂)_p—

,

R⁶⁰ represents methyl, ethyl, benzyl or phenyl,

n represents an integer from 1 to 10,

m and p independently of one another represent an integer from 0 to 4,

represents an integer from 0 to 2 and

t represents an integer from 1 to 6.

8. An electrochromic system as claimed in claim 6, which comprises at least one substance of the formula (Ia)-(Id)

in which

OX₂ represents a radical of the formulae (II), (IV) or (V),

in which

R², R⁴ and R⁸ represent a direct bond to the bridge member B,

R³, R⁵ and R⁹ independently of one another represent methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, benzyl or phenyl, or in the case of the formulae Ic or Id, also represent a direct bond to the bridge member B,

R⁶ and R⁷ are identical or different and represent hydrogen, methyl, methoxy, chlorine, cyano or methoxycarbonyl,

R¹⁰, R¹¹;

R¹², R¹³ and R¹⁴, R¹⁵ independently of one another represent hydrogen or, if Z¹ denotes a direct bond, in each case in pairs together represent a —

CH═

CH—

bridge,

R⁶⁹ to R⁷² are identical and denote hydrogen, methyl or ethyl,

R⁷³ and R⁷⁴ denote hydrogen,

E¹ and E² are identical and represent O or S,

Z¹ represents a direct bond or —

CH═

CH—

,

X⁻

represents a colorless anion which is redox-inert under the conditions,

RED₁ represents a radical of the formulae (X), (XII), (XIII), (XVI) or (XVII),

R²⁸, R³⁴, R³⁸, R⁴⁶ and R⁴⁹ represent a direct bond to the bridge member B,

R²⁹ to R³¹, R³⁵ and R³⁹ independently of one another represent methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, benzyl or phenyl, or

R³⁰, R³⁵ and R³⁹ in the case of the formulae Ib and Ic also represent a direct bond to the bridge member B,

R³², R⁴⁷ and R⁴⁸ represent hydrogen,

R³⁶, R³⁷, R⁴⁰, R⁴¹ and R⁵⁰ to R⁵² independently of one another represent hydrogen, methyl, methoxy, chlorine, cyano, methoxycarbonyl or phenyl, or,

R⁵¹ in the case of the formulae Ib and Id also represent a direct bond to the bridge member B,

Z³ represents a direct bond or a —

CH═

CH—

or —

N═

N—

bridge,

═

Z⁴═

represents a direct double bond or a ═

CH—

CH═

or ═

N—

N═

bridge,

E³ to E⁵ independently of one another represent O, S or NR⁵⁹, but E³ and E⁴ have the same meaning,

E⁶ to E⁹ are identical to one another and represent S, Se or NR⁵⁹,

R⁵⁹ represents methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, benzyl or phenyl, or

R⁵⁹ in the case of the formula XVI in formula Ib or Id also represents a direct bond to the bridge member B,

B represents a bridge member of the formulae —

(CH₂)_n—

, —

(CH₂)_m—

O—

(CH₂)_p—

, —

(CH₂)_m—

NR⁶⁰—

(CH₂)_p—

, —

(CH₂)_m—

C₆H₄—

(CH₂)_p—

, —

[O—

(CH₂)_p]—

O—

, —

NR⁶⁰—

(CH₂)_p—

NR⁶⁰—

, —

(CH₂)_m—

OCO—

C₆H₄—

COO—

(CH₂)_p—

, —

(CH₂)_m—

NHCO—

C₆H₄—

CONH—

(CH₂)_p—

, —

(CH₂)_m—

NHCONH—

C₆H₄—

NHCONH—

(CH₂)_p—

, —

(CH₂)_m—

OCO—

(CH₂)_t—

COO—

(CH₂)_p—

, —

(CH₂)_m—

NHCO—

(CH₂)_t—

CONH—

(CH₂)_p—

, —

(CH₂)_m—

NHCONH—

(CH₂)_t—

NHCONH—

(CH₂)_p—

,

R⁶⁰ represents methyl,

n represents an integer from 1 to 10,

m and p are identical and represent an integer from 0 to 2 and

t represents an integer from 1 to 6.

9. An electrochromic system as claimed in claim 1, which comprises at least one electrochromic substance of the formula (Ia)

14. An electrochromic liquid comprising an electrochromic system as claimed in claim 1 and at least one inert solvent.

15. An electrochromic device comprising an electrochromic liquid as claimed in claim 14.

16. An electrochromic device as claimed in claim 15, which is constructed as a cell.

17. An electrochromic device as claimed in claim 15, which comprises two transparent panes of glass or plastic facing one another, one of which is optionally metallized and the sides of which facing one another are coated with an electrically conductive coating, the electrochromic liquid being contained between the two panes.

18. An electrochromic device as claimed in claim 16, wherein the cell is constructed as a solar cell, or as a window pane, mirror, sunroof or display.

10. An electrochromic substance corresponding to the formula

in which

Y and Z independently of one another represent a radical OX₂ or RED₁ but in which at least one Y represents OX₂ and at least one Z represents RED₁,

in which

OX₂ represents the radical of a reversibly electrochemically reducible redox system and

RED₁ represents the radical of a reversibly electronically oxidizable redox system, where the radical of the formula (XX)

where

R⁶¹ to R⁶⁸ independently of one another denote hydrogen, C₁- to C₆-alkyl, C₁- to C₄-alkoxy, cyano, C₁- to C₄-alkoxycarbonyl or C₆- to C₁₀-aryl, or

R⁶¹, R⁶² and R⁶⁷;

and R⁶⁸ independently of one another together form a —

(CH₂)₃—

, —

(CH₂)₄—

or —

CH═

CH—

CH═

CH—

bridge,

v denotes an integer between 0 and 10, is excluded,

B represents a bridge member,

c represents an integer from 0 to 5 and

a and b independently of one another represent an integer from 0 to 5,

with the exception of compounds of the formula

in which

m represents an integer from 2 to 16 and

X⁻

represents a colorless anion which is redox-inert under the conditions.

11. An electrochromic substance according to claim 10 corresponding to one of the formulae

12. An electrochromic substance as claimed in claim 10 of the formulae

or at least one substance of the formula (Ic) corresponding to one of the formulae

in which

R³, R⁵, R³⁵ and R³⁹ independently of one another represent methyl, ethyl, propyl, butyl, pentyl, hexyl or benzyl,

R⁶, R⁷ and R³⁶, R³⁷ in pairs are identical and represent hydrogen, methyl, methoxy, chlorine, cyano or methoxycarbonyl,

R¹² and R¹³ represent hydrogen or, if Z¹ denotes a direct bond, together represent a CH═

CH bridge,

RE⁶⁹ to R⁷² are identical and represent hydrogen or methyl,

E¹ and R² are identical and represent O or S,

Z¹ represents a direct bond or —

CH═

CH—

,

R³², R⁴⁷ and R⁴⁸ represent hydrogen,

E³ to E⁵ independently of one another represent O, S or NR⁵⁹, but where E³ and E⁴ are identical,

R²⁹ to R³¹ and R⁵⁹ independently of one another represent methyl, ethyl, propyl, butyl, pentyl, hexyl or benzyl, where R²⁹ to R³¹ are preferably identical,

R⁴⁰ and R⁴¹ are identical and represent hydrogen, methyl, ethyl, propyl, butyl or phenyl,

Z³ represents a direct bond, —

CH═

CH—

or —

N═

N—

,

R⁵⁰ to R⁵² independently of one another represent hydrogen, methyl, methoxy, chlorine, cyano, methoxycarbonyl, ethoxycarbonyl or phenyl, but are preferably identical,

E⁶ to E⁹ are identical to one another and represent S, Se or NR⁵⁹,

Z⁴ represents a direct double bond or a ═

CH—

CH═

—

or ═

N—

N═

bridge,

m represents an integer from 1 to 5,

u represents 0 or 1 and

X⁻

represents a colorless anion which is redox-inert under the conditions.

13. A process for the preparation of an electrochromic substance as claimed in claim 10, which comprises reacting a compound of the formula

19. An electrochromic substance as claimed in claim 10, wherein a and b independently represent an integer from 0 to 3.