Colored electroscopic toners containing quenched esterified rhodamine dyes

DETAILED DESCRIPTION OF THE INVENTION In accordance with the present invention, there is provided a colored electroscopic toner comprising: (1) a polymeric binder, (2) a rhodamine dye having a non-lactonizing ester-containing phenyl group in the 9-position, and (3) a quencher dye.
Typically the esterified rhodamine dye has the structure: ##STR2## where each of R.
sup.
1, R.
sup.
2, R.
sup.
3, R.
sup.
4, R.
sup.
5 and R.
sup.
6 is H or an alkyl group, n is from 1 to 18 and X.
sup.
- is an anion.
A phenyl group is substituted at the 9-position of the substituted xanthene nucleus of the rhodamine dye.
The phenyl group contains a non-lactonizing ester group, typically substituted at the ortho position.
In one embodiment of the present invention, the non-lactonizing ester group is an ester of a monocarboxylic acid, often containing up to 19 carbon atoms.
Typically, it is an ester of a lower monocarboxylic acid containing 1-8 carbon atoms, e.
g.
, methoxycarbonyl, ethoxycarbonyl or propoxycarbonyl.
The concentration of rhodamine dye used in practicing this invention is subject to wide variation.
A typical concentration is about 1 to 10, often 2 to 5 weight percent, based on polymeric binder in the toner.
One advantage of the ionic esterified rhodamine dyes over zwitterionic rhodamine free bases, i.
e.
, rhodamines which form neutral internal-salts, resides in the flexibility attained from the ability to select an anion (X.
sup.
-).
The anion can be selected from a wide variety of anions, including trifluoromethanesulfonate (CF.
sub.
3 SO.
sub.
3.
sup.
-), naphthalene disulfonate (C.
sub.
10 H.
sub.
8 (SO.
sub.
3).
sub.
2.
sup.
=), para-toluenesulfonate (H.
sub.
3 C--C.
sub.
6 H.
sub.
5 --SO.
sub.
3.
sup.
-), hexafluorophosphate (PF.
sub.
6.
sup.
-), perchlorate (ClO.
sub.
4.
sup.
-), meta-nitrobenzenesulfonate (O.
sub.
2 N--C.
sub.
6 H.
sub.
5 --SO.
sub.
3.
sup.
-) and meta-aminobenzenesulfonate (H.
sub.
2 N--C.
sub.
6 H.
sub.
5 --SO.
sub.
3.
sup.
-).
Fluorescence-quenching dyes useful in the practice of the present invention absorb radiation at the same wavelengths as the radiation that is emitted by the rhodamine dye used in the toner