Synthesis and Thermal Stability of Solvent Soluble Dyes Based on Dimerized Diketo-pyrrolo-pyrrole Pigment

Experimental Section

3,6-Bis(4-chlorophenyl)-2-octylpyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (N-alkylated Red 254). 6.27 g (14.2 mmol) of 1,4-diketo-3,6-bis-(4-biphenyl)-pyrrolo-[3,4-c]- pyrrole was suspended in 90 ml of 1-methyl-2-pyrrolidinone for two hours at room temperature. 3.87 g (34.5 mmol) of potassium tert.-butoxide was added to this slurry under a nitrogen atmosphere. After stirring for one hour, 5.79 g (30 mmol) of 1-bromooctane was added to the reaction mixture and then the mixture stirred additionally for two hours. The mixture was poured into 150 mL of water and the red solid filtered off. Subsequent isolation of the mono-substituted component (N-alkylated Red 254) was carried out by adding the crude product to a mixture of n-hexane (30 mL) and chloroform (3 mL). After stirring for further 5 minutes in the same condition, the precipitated solid was filtered and sub-sequently washed with a mixture of n-hexane (10 mL) and chloroform (3 mL). The filtered solid was dried under vacuum to obtain N-alkylated Red 254.

N-Alkylated Red 254: Yield: 45%, Found C: 67.25 H: 5.64 N: 6.47 O: 6.23 Calculated C26H26Cl2N2O2 C: 66.53 H: 5.58 N: 6.82 O: 6.82, MS469 (M+).

5,5'-Alkylenebis(3,6-bis(4-chlorophenyl)-2-octylpyrrolo-[3,4-c]pyrrole-1,4(2H,2H)-dione) (Dye 1). The obtained 5 g (1.1 mmol) was slurried in 70 mL of 1-methyl-2-pyrrolidi-none for 15 min at room temperature. 1.673 g (1.5 mmol) of potassium tert-butoxide was added to the slurry under a nitrogen atmosphere. After stirring for one hour, 2.04 g (0.6 mmol) of diiodinemethane was added to the reaction mix-ture and then the mixture stirred additionally for three hours. The mixture was poured into 100 mL of water and the red solid filtered off and purified by column chromatography (silica gel, dichloromethane as an eluent). After drying, 0.98 g of a red solid of Dye 1 was obtained.

Dye 1: Yield: 27%, Found C: 67.01 H: 6.02 N: 5.42 O: 6.34 Calculated C53H52Cl4N4O4 C: 66.95 H: 5.51 N: 5.89 O: 6.73, MS 950 (M+).

Other dyes were obtained by same procedure except reaction temperature (Dye 2: 1,4-diiodobutane, Dye 3: 1,8-diiodoctane).

Dye 2: Yield: 31%, Found C: 68.32 H: 6.01 N: 5.32 O: 6.10 Calculated C56H58Cl4N4O4 C: 67.74 H: 5.89 N: 5.64 O: 6.45, MS 992 (M+).

Dye 3: Yield: 37%, Found C: 69.11 H: 5.67 N: 5.21 O: 5.90 Calculated C60H66Cl4N4O4 C: 68.70 H: 6.34 N: 5.34 O: 6.10, MS 1048 (M+).

Solubility Test. The dye was added PGMEA (20 mL) and then stirred at room temperature for 30 mins. The supersaturated solution was passed through a 0.45 μm syringe filter. The filtered solid was dried at 65 ℃ and then weighed to determine the amount of dissolved dye in order to calculate the solubility of the dye.

Fabrication of Color Filter. Spin-coating was carried out onto glass using a MIDAS System SPIN-1200D spin-coater. The glass was spun at a low to moderate speed of 300 rpm for 10 seconds to evenly spread the solution (dye-based ink). The solution was prepared with synthesized dyes, a solvent (PGMEA) and a binder based on acrylate. Once spin-coating was completed, the film was placed quickly onto a hot plate and heated to around 100 ℃ for 5 minutes to evaporate the solvent.

Thermal Stability Test as Color Filter. The thermal stability of synthesized dyes after fabrication was measured by prebaking at 90 ℃ for 90 seconds and post-baking at 220 ℃ for 40 mins, then additionally heating for 1 h at 240 ℃, thereafter color differences in Eab were determined using an MCPD 3700.