## 3 Results and Discussions  
The absorption coefficients of EBT3 films versus UV exposure obtained from our model are shown in Figure 6. The increase in the absorption coefficient with increasing UV exposure could be explained in the atomic scale by the corresponding increase in the density of the system. The extra energy from larger UV exposures increased the kinetic energy of atoms in the monomer strands and facilitated their relocation to form a cross-linked structure. A denser polymerized configuration through solid-state polymerization would result from more bond formation. The lowest and highest absorption coefficients were found to be ~27.0 and ~29.0 cm\({}^{-1}\), respectively. The absorption coefficients were obtained from the product of mass energy-absorption coefficient with density. Here, the mass energy-absorption coefficient was assumed to be 100 cm\({}^{2}\)/g, but the chosen value was not important since _Net ROD_ was the ratio of reflected intensities from the unexposed and exposed film to UV radiation. The variations in reflected light intensities from the EBT3 film were governed by the variation in density \(\rho\) versus UV exposure in other words, by the variation in absorption coefficient  
Figure 4: Flowchart summarizing approach to determine _Net ROD_. Figure 5: Irradiation of the EBT3 film and the reflection from the film. \(\mu_{\alpha}\) versus UV exposure, since \(\mu_{\alpha}=\rho\times(\mu_{\alpha})_{m}\). A snapshot from the atomic-scale system of monomer strands during relaxation after UV exposure and subsequent formation of bonds is shown in Figure 7.  
The reflected intensities (i.e., \(log(\phi)\)) from the EBT3 films versus UV exposures are shown in Figure 8. A larger absorption coefficient led to increased absorption of light by the polymer material. For UV exposures larger than \(\sim\)40 J/cm\({}^{2}\), the reflected light intensity decreased at a lower rate when compared to other UV exposure values, which was due to the insignificant variations in the absorption coefficient for UV exposures larger than \(\sim\)40 J/cm\({}^{2}\) (see Figure 6). For relatively large UV exposures, the monomers became almost fully polymerized, and the densely cross-linked structure significantly lowered the efficiency for further bond formation between DA monomer strands. As a result, the absorption coefficient, which depended on the density of polymerization, also did not significantly increase at large UV exposures. Figure 6: Absorption coefficients of EBT3 film versus ultraviolet (UV) light exposure obtained from our model. Figure 7: A snapshot from the atomic-scale system of monomer strands during relaxation after UV exposure and subsequent formation of bonds. (Red spheres: carbon atoms; blue spheres: hydrogen atoms. Dimensions of box: 800 \(\times\) 230 \(\times\) 150 Å\({}^{3}\)). In the model here, _Net ROD_ was defined as _Net ROD = log(\(\phi_{unexposed}\)/\(\phi_{exposed}\))_, where \(\phi_{unexposed}\) and \(\phi_{exposed}\) were reflected intensities of light from the unexposed and exposed film to UV radiation, respectively, in line with the definition of experimental _Net ROD_ as _Net ROD = log(\(P_{u}\)/\(P_{t}\))_, where \(P_{u}\) and \(P_{t}\) were the pixel values of reflected intensities through an unexposed film and an exposed film, respectively [8]. It is remarked here that, during the conversion of experimentally obtained images of the EBT3 film into grayscale, the pixel values ranged from 255 (completely white) to 0 (completely black), so the ratio \(P_{u}\)/\(P_{t}\) was always larger than unity. Similarly, the ratio \(\phi_{unexposed}\)/\(\phi_{exposed}\) ratio was always larger than unity. Both pixel values and reflected light intensities could be traced back to properties of the EBT3 film under analysis. The comparisons among _Net ROD_ values (obtained experimentally by [PERSON] et al.