We Claim:
1. A substantially pure Indocyanine green of formula (1) having purity greater than 99.0% by HPLC.
2. The indocyanine green of formula (1) according to claim 1 having purity greater
than 99.0% by HPLC and characterized by one or more of the following:
(i) less than 0.15% of impurity A; (ii) less than 0.15 % of impurity B; (iii) less than 0.15% of impurity C; and (iv) combination of lead and Arsenic is less than 2ppm
3. An improved process for the preparation of Indocyanine green of formula (1)
having purity greater than 99.0% comprising the steps of:
a) reacting l,l,2-trimethyl-lH-benzo[e]indole of formula (5)

with 1,4-butane sultone to form 4-(l,l,2-trimethyl-lH-benzo[e]indolium-3-yl) butane-1-sulfonate of formula (4);
b) treating formula (4) with E-N-((2E,4E)-5-(phenyl amino) penta-2,4-dienylidene) aniline hydrochloride of formula (3)
in presence of acetic anhydride to form 4-(l,l-dimethyl-2-((lE,3E,5E)-6-(N-phenyl acetamido) hexa-l,3,5-trienyl)-lH-benzo [e] indolium-3-yl) butane-1-sulfonate of formula (2);
c) reacting formula (2) with formula (4) in presence of a base to obtain 4-amino-N-(2-(diethylamino) ethyl) benzamide hydrochloride of formula (1); and
d) purifying 4-amino-N-(2-(diethylamino) ethyl) benzamide hydrochloride or Indocyanine green of formula (1), wherein the purification process comprises:

1) suspending Indocyanine green of formula (1) in a suitable solvents or mixtures thereof;
2) heating the reaction mixture at suitable temperature;
3) filtering the reaction mixture at suitable temperature; and
4) isolating from a suitable solvents or mixture thereof.

4. The process according to claim 3, wherein the base used in step c) is selected from a group consisting of triethylamine, pyridine, ammonia, potassium carbonate, sodium carbonate, potassium bicarbonate, sodium bicarbonate, potassium hydroxide or sodium hydroxide.
5. The process according to claim 3, wherein the solvent used in step d) is selected from a group consisting of acetone, methanol, ethanol, isopropyl alcohol (IPA), n-propanol, n-butanol, or mixtures thereof.
6. A process for the purification of Indocyanine green of formula (1), which comprises:

1) suspending Indocyanine green of formula (1) in a suitable solvents or mixture thereof;
2) heating the reaction mixture at suitable temperature;
3) filtering the reaction mixture at suitable temperature; and
4) isolating from a suitable solvents or mixture thereof.
7. The process according to claim 6, wherein the solvent is selected from the group
consisting of acetone, methanol, ethanol, isopropyl alcohol (IPA), n-propanol,
n-butanol, or mixtures thereof.
8. The process according to claim 6, purification of Indocyanine green of formula
(1) comprises of:
1) suspending Indocyanine green of formula (1) in a mixture of
methanol and isopropyl alcohol;
2) heating the reaction mixture to 60-80°C;
3) filtering the reaction mixture at 60-75°C; and
4) isolating from isopropyl alcohol.
9. A crystalline form I of Indocyanine green of formula (1) characterized by X-ray
powder diffraction (XRPD) pattern comprising peaks at 2 theta values 3.30, 4.86
degrees 2 theta (26°) as shown in figure-1.
10. A process according to claim 3, wherein the preparation of formula (3)
comprises of the following steps:
i. reacting l-chloro-2,4-dinitrobenzene of formula (7)

with pyridine to form l-(2,4-dinitrophenyl) pyridinium chloride of formula
ii. reacting formula (6) with methanolic aniline to form N-((2E,4E)-5-(phenyl amino) penta-2,4-dienylidene) aniline hydrochloride of formula (3); and
iii. purifying N-((2E,4E)-5-(phenyl amino) penta-2,4-dienylidene) aniline hydrochloride of formula (3).