The broad-spectrum biocide triclosan trigonal crystal: Experimental and DFT-calculated structural, electronic and optical properties

•X-ray and photoacoustic-based optical absorption measurements were performed on the triclosan crystal.•DFT calculations using dispersion corrections provided lattice parameters close to experiment.•Triclosan has a direct band gap around 3.44 eV were estimated, matching PA absorption measurement.•Calculated optical absorption and complex dielectric function reveal the optical isotropy of triclosan.•Effective masses show that triclosan can behave as a wide direct gap semiconductor. Triclosan, a member of the broad-spectrum biocide class, has seen widespread usage in various household and healthcare-related products worldwide over the past 35 years. However, its extensive use has raised concerns regarding health and environmental impacts. Notably, there is a notable gap in our understanding of the solid-state properties of triclosan, encompassing both experimental aspects, such as optical absorption, and theoretical insights. Expanding upon the established trigonal crystal structure of triclosan, this study employs experimental techniques including X-ray and photoacoustic-based optical absorption, alongside density functional theory (DFT) calculations, to elucidate its structural, electronic, and optical characteristics. Employing the generalized gradient approximation (GGA) DFT exchange-correlation functional and accounting for dispersion effects, optimal lattice parameters were determined with small deviations from experimental measurements (