Fluoran compounds, which are a type of colorless dye (color former), develop color via a ring-opening reaction when interacted with acids (developer), as shown in the following scheme. Because this reaction is reversible, decoloration occurs in a reversible manner under basic conditions.

Pressure and heat sensitive recording systems utilize this color developing mechanism in which color formers, developers and sensitizers are intimately incorporated. In pressure sensitive recording, the coloration occurs as follows: Capsules containing color former are destroyed by pressure and the color former makes contact with the developer coated support material. In heat sensitive recording, both color former and developer, which are dispersed on the support material, are thermally melted, thus contacting each other to initiate the coloring reaction. Furthermore, a low melting point sensitizer is also added to achieve a high sensitivity. Recently, the technique has been applied to re-writable recording paper, which can be used for repeated writing and erasing. This technique has been applied to print on commuter passes or prepaid cards. By combining acid-generating methods with the coloring mechanism, new applications can be expected for these materials.

Color Formers

Developers

Sensitizers

Color Formers

C1946	D3204	B2628
D3205	D3201	D3203
D3202	B0207	C0741

C1946	2'-(2-Chloroanilino)-6'-(dibutylamino)fluoran
D3204	2'-(Dibenzylamino)-6'-(diethylamino)fluoran
B2628	3',6'-Bis(diethylamino)-2-(4-nitrophenyl)spiro[isoindole-1,9'-xanthene]-3-one
D3205	3',6'-Dimethoxyfluoran
D3201	3-(1,2-Dimethyl-3-indolyl)-3-[4-(diethylamino)-2-methylphenyl]phthalide
D3203	6'-(Diethylamino)-1',2'-benzofluoran
D3202	6'-(Diethylamino)-1',3'-dimethylfluoran
B0207	Benzoyl Leuco Methylene Blue
C0741	Crystal Violet Lactone

Developers

M1410	T1254	B2752
B2753	B1568	B2664
N0026	B0813	B2750
B2749	B2748	B2751
B1567	B0494	T2259
N0027	D3267	E0664
H1166	B0464	D2121
B0819	E0432	M1684
T0144	P0201	B0735
B1715	B1563	T1428
H0209	D1356	B0495
H0216	R0008	T0032

M1410	1,1'-Methylenedi-2-naphthol
T1254	1,1,1-Tris(4-hydroxyphenyl)ethane
B2752	1,1-Bis(3-cyclohexyl-4-hydroxyphenyl)cyclohexane
B2753	1,1-Bis(4-hydroxy-3-methylphenyl)cyclohexane
B1568	1,1-Bis(4-hydroxyphenyl)cyclohexane
B2664	1,3-Bis[2-(4-hydroxyphenyl)-2-propyl]benzene
N0026	1-Naphthol
B0813	2,2'-Biphenol
B2750	2,2-Bis(2-hydroxy-5-biphenylyl)propane
B2749	2,2-Bis(3-cyclohexyl-4-hydroxyphenyl)propane
B2748	2,2-Bis(3-sec-butyl-4-hydroxyphenyl)propane
B2751	2,2-Bis(4-hydroxy-3-isopropylphenyl)propane
B1567	2,2-Bis(4-hydroxy-3-methylphenyl)propane
B0494	2,2-Bis(4-hydroxyphenyl)propane
T2259	2,3,4-Trihydroxydiphenylmethane
N0027	2-Naphthol
D3267	4,4'-(1,3-Dimethylbutylidene)diphenol
E0664	4,4'-(2-Ethylhexylidene)diphenol
H1166	4,4'-(2-Hydroxybenzylidene)bis(2,3,6-trimethylphenol)
B0464	4,4'-Biphenol
D2121	4,4'-Dihydroxydiphenyl Ether
B0819	4,4'-Dihydroxydiphenylmethane
E0432	4,4'-Ethylidenebisphenol
M1684	4,4'-Methylenebis(2-methylphenol)
T0144	4-(1,1,3,3-Tetramethylbutyl)phenol
P0201	4-Phenylphenol
B0735	4-tert-Butylphenol Zone Refined (number of passes:19)
B1715	9,9-Bis(4-hydroxyphenyl)fluorene
B1563	alpha,alpha'-Bis(4-hydroxyphenyl)-1,4-diisopropylbenzene
T1428	alpha,alpha,alpha'-Tris(4-hydroxyphenyl)-1-ethyl-4-isopropylbenzene
H0209	Benzyl 4-Hydroxybenzoate
D1356	Bis(4-hydroxyphenyl) Sulfide
B0495	Bis(4-hydroxyphenyl) Sulfone
H0216	Methyl 4-Hydroxybenzoate
R0008	Resorcinol
T0032	Tetrabromobisphenol A

Sensitizers

D0910	D0159	D2017
D1598	B1519	B1248
B1619	D0001	T0015
C0043	P0231	D0866
F0016	F0017	H0067
C0024	L0011	T0018
H0283	M0476	O0238
O0107	P0002	H0797
S0075	S0314

D0910	1,3-Diphenyl-1,3-propanedione
D0159	1,4-Dibenzyloxybenzene
D2017	1,4-Diphenoxybenzene
D1598	2,6-Diisopropylnaphthalene
B1519	4-Benzylbiphenyl
B1248	Behenic Acid
B1619	Benzyl 2-Naphthyl Ether
D0001	Dibenzyl Sulfoxide
T0015	Dimethyl Terephthalate
C0043	Diphenyl Carbonate
P0231	Diphenyl Sulfone
D0866	Ethylene Glycol Diphenyl Ether
F0016	Fluoranthene
F0017	Fluorene
H0067	Hexadecanamide
C0024	Hexanamide
L0011	Lauric Acid
T0018	m-Terphenyl
H0283	Methyl 3-Hydroxy-2-naphthoate
M0476	Myristic Acid
O0238	n-Octanamide
O0107	Oleamide
P0002	Palmitic Acid
H0797	Phenyl 1-Hydroxy-2-naphthoate
S0075	Stearamide
S0314	Stearanilide