## 3 Results and Discussion
of a broad peak in the UV-visible spectrum is due to the presence of conjugated systems or electronic transitions within the molecules. Conjugated systems, which consist of alternating single and double bonds or aromatic structures, are responsible for the absorption in the UV region. The broader the peak, the more complex the conjugated system or the greater the number of electronic transitions involved. The factors contributing to the broadening of peaks in the UV spectrum are longer conjugation lengths, \(\pi\)-\(\pi^{\ast}\) electronic transitions, and the molecular structure. Siam weed contributed to the peak at 656 nm, indicating chlorophyll in the biocomposite. From Figure 5d, it can be observed that adding more Siam weed extract does not significantly affect the optical absorption (i.e., the absorbance level increases from sample BC1 to BC2 and, further, there is no significant change in BC3). The Tauc plot analysis of Figure 5a-c yields direct bandgap energies of 2.08 eV, 2.14 eV, and 2.05 eV for the BC1, BC2, and BC3 samples, respectively. Photoluminescence (PL) spectral studies of biopackaging materials provide valuable information about their optical and photophysical characteristics. The emission peaks and intensity in the PL spectrum can indicate the material's composition and molecular arrangement and the presence of specific fluorophores or chromophores. By studying the PL properties of bioplastic packaging materials, researchers can gain insights into their fluorescence behaviour, which is crucial for product labelling or tracking applications. The PL spectra of BC1, BC2, and BC3 for the excitations 300 nm, 350 nm, 400 nm, and 450 nm are shown in Figure 6. All the samples exhibited broad emissions at 425 nm irrespective of the excitation. The addition of Siam weed lowered the emission intensity (i.e., the emissions decrease from the BC1 sample to the BC2 sample and, further, there is  
Figure 5: UV–visible absorption spectrum of samples: (**a**) BC1, (**b**) BC2, and (**c**) BC3; (**d**) absorbance at 360 nm for all three samples. no significant change in BC3). A representative variation in the emission intensity peak at 440 nm corresponding to the excitation at 350 nm is shown in Figure 6e. When the PL spectrum is analysed in light of Figure 5, it is observed that although the absorbance level increases from BC1 to BC2, the emission behaviour is just the opposite. The optical energy distribution in the emission spectrum can be understood from the power spectral analysis and the colour purities of the emissions from the CIE plot. The representative power spectrum and CIE plot corresponding to the 350 nm excitation are shown in Figures 7 and 8, respectively. The samples BC1, BC2, and BC3 exhibited emissions in the blue region with colour purities of 38.5%, 48.5%, and 50.1%, respectively. From the PL analyses, it can be inferred that more energy was dissipated by non-radiative deexcitation, raising the system enthalpy. The change in enthalpy can help with the biological activity of the sample, which is understood from the antimicrobial studies. Figure 6: PL spectra of samples for the wavelengths (\(\lambda\)) of excitations at (**a**) 300 nm, (**b**) 350 nm, (**c**) 400 nm, and (**d**) 450 nm; (**e**) variation in emission intensity peaks at 440 nm corresponding to the excitation at 350 nm. Antibacterial analysis helps determine the biocomposite's potential to inhibit or reduce the growth of bacteria, providing valuable information for applications in fields such as medical devices and food packaging. In the present study, the antibacterial properties of the biocomposites against the Gram-negative _Staphylococcus aureus_ and Gram-positive _Pseudomonas aeruginosa_ were investigated.