# Novel Yellow Aromatic Imine Derivative Incorporating Oxazolone Moiety for Color Resist Applications
## 3 Results and Discussion  
The commercially utilized 9-methoxy-7H-benzo[de]benzo[4,5]imidazo[2,1-a]isoquinolin-7-one (MBIQO), exhibiting yellow color characteristics, demonstrates excellent optical properties suitable for application as a color filter material for image sensors due to its aromatic imine group [20; 21; 22; 23; 24; 25; 26]. We conducted molecular design of a novel yellow colorant capable of enhancing absorption characteristics while retaining the aromatic imine group and functional groups present in MBIQO. The newly designed aromatic imine derivative, PBMBO, incorporates a benzene and (E)-4-(4-methoxybenzylidene)oxazol-5(4H)-one moiety. In synthetic compounds, a dimeric arrangement is prepared, where the structure contains an (E)-4-(4-methoxybenzylidene)oxazol-5(4H)-one framework comprising a phenyl core alongside an oxazolone and a methoxy group, connected on both ends. This dimerization is anticipated to enhance solvent interaction compared to conventional MBIQO, leading to increased solubility. Additionally, it is expected to improve absorbance through electron delocalization. The structural formula and synthesis pathway of the synthesized PBMBO are illustrated in Schemes 1 and 2. The synthesized compound was purified through a column and reprecipitation process, and its structure was confirmed via NMR spectroscopy (Figure S1). The optical data in solution state of the newly synthesized yellow colorant, PBMBO, are presented in Figure 1 and Table 1. The measurements of absorbance and transmittance of PBMBO were conducted under conditions suitable for image sensor applications, utilizing a 1 \(\times\) 10\({}^{-4}\) M solution in PGMEA. The requirements for the molecular extinction coefficient of yellow colorants in image sensor applications are above 1.0 \(\times\) 10\({}^{4}\) L/mol\(\cdot\)cm, and the transmittance criteria are less than 5% at 435 nm and over 90% at 530 nm. The molecular extinction coefficient values were calculated using the Beer-Lambert law formula to evaluate the optical absorption properties of yellow colorants. \[\text{A}=\varepsilon cl \tag{1}\]A: absorbance; \(\varepsilon\): molecular extinction coefficient; \(c\): molar concentration; \(l\): optical path length UV-Vis absorption spectroscopy is a method used to determine the range and intensity of wavelengths absorbed by a material in the 200-800 nm range. Absorption occurred in the 400-500 nm range for both synthesized materials, with maximum absorption wavelengths observed at 410 nm for MBIQO and 434 nm for PBMBO. While absorption intensity is typically expressed in the range of 0-1, the synthesized materials exhibited absorption intensities greater than 1 even at a low concentration of 1 \(\times\) 10\({}^{-4}\) M, owing to their extremely high molecular extinction coefficients and despite being dilute solutions. The molecular extinction coefficient values at the maximum absorption wavelengths of MBIQO and PBMBO were 1.23 \(\times\) 10\({}^{4}\) and 2.24 \(\times\) 10\({}^{4}\) L/mol\(\cdot\)cm at 410 nm and 434 nm, respectively. Therefore, both MBIQO and PBMBO demonstrated molecular extinction coefficient values of over 1.0 \(\times\) 10\({}^{4}\) L/mol\(\cdot\)cm in PGMEA solvent, indicating their excellence as yellow colorant candidates. While both MBIQO and PBMBO exhibited absorption in the same range of 400-500 nm, PBMBO showed a significantly enhanced molecular extinction coefficient value, being 1.82 times higher than MBIQO. This increase in the molecular extinction coefficient value is interpreted as the result of the excellent absorption characteristics of the oxazolone moiety, which enhances the absorption properties when forming the colorant in a dimeric form [27; 28; 29; 30]. Consequently, the transmittance spectra of both yellow colorants exceeded the requirements of image sensor applications. As indicated in Table 1, the transmittance of PBMBO was 0.58% and 95.9%, respectively, while MBIQO at 435 nm and 530 nm was 4.3% and 99.8%. Both materials satisfied the transmittance requirements.