Molecular modeling as a design tool for sunscreen candidates: a case study of bemotrizinol

Porphyrin and phthalocyanine heavy metal removal: overview of theoretical investigation for heterojunction organic solar cell applications

CONTEXT

Heavy metals are highly noxious, and their presence can cause diverse effects on living organisms and the environment. Crown ether porphyrins and phthalocyanines are known to effectively extract these pollutants and are also used in photovoltaic devices. This study aims to evaluate various factors that govern intramolecular charge transfer (ICT) and photo-injection processes, including maximum absorption wavelength (λ_max), density of states (DOS), charge transfer dipole (μ_CT), light harvesting efficiency (LHE), open-circuit voltage (V_oc), and free energy change of electron injection (ΔG_inj) in order to investigate the performance of different compounds designed from metalloporphyrins for bulk-heterojunction organic solar cell (BHJ-OSC) applications. The porphyrin complex showed the best optoelectronic properties, with remarkable LHE values and CT amounts compared to phthalocyanine derivatives. The central metal played a significant role in optimizing the optical properties of the materials for use in solar cells. HgPr4O and CdPr4O were found to have optimal V_oc values, resulting in effective injection, high electron, and hole mobilities, making them ideal materials for highly efficient BHJ-OSC devices.

METHODS

Density functional theory (DFT) approach was employed with the B3LYP functional and the def2TZVP basis set as implemented in the Gaussian 16 revision C.01 program to investigate the designed complexes and to compute geometrical parameters, frontier molecular orbitals (FMOs), and natural bond orbital (NBO). Furthermore, the time-dependent density functional theory (TD-DFT) method was used to analyze the optical properties and photovoltaic characteristics of selected metalloporphyrins by examining the UV-Vis spectra. In summary, the study presents a thorough description of the structural and electronic properties of the investigated complexes and provides insights into their potential use in photovoltaic applications.

The photoprotection mechanism in the black-brown pigment eumelanin

The natural black-brown pigment eumelanin protects humans from high-energy UV photons by absorbing and rapidly dissipating their energy before proteins and DNA are damaged. The extremely weak fluorescence of eumelanin points toward nonradiative relaxation on the timescale of picoseconds or shorter. However, the extreme chemical and physical complexity of eumelanin masks its photoprotection mechanism. We sought to determine the electronic and structural relaxation pathways in eumelanin using three complementary ultrafast optical spectroscopy methods: fluorescence, transient absorption, and stimulated Raman spectroscopies. We show that photoexcitation of chromophores across the UV-visible spectrum rapidly generates a distribution of visible excitation energies via ultrafast internal conversion among neighboring coupled chromophores, and then all these excitations relax on a timescale of ∼4 ps without transferring their energy to other chromophores. Moreover, these picosecond dynamics are shared by the monomeric building block, 5,6-dihydroxyindole-2-carboxylic acid. Through a series of solvent and pH-dependent measurements complemented by quantum chemical modeling, we show that these ultrafast dynamics are consistent with the partial excited-state proton transfer from the catechol hydroxy groups to the solvent. The use of this multispectroscopic approach allows the minimal functional unit in eumelanin and the role of exciton coupling and excited-state proton transfer to be determined, and ultimately reveals the mechanism of photoprotection in eumelanin. This knowledge has potential for use in the design of new soft optical components and organic sunscreens.

Identification of Triazine UV Filters as an Emerging Class of Abundant, Ubiquitous Pollutants in Indoor Dust and Air from South China: Call for More Concerns on Their Occurrence and Human Exposure

Triazine UV filters are an important class of UV filters, but knowledge on their environmental occurrence and human exposure remains largely unknown. In this study, we performed a targeted analysis of 17 emerging triazine UV filters in indoor dust and indoor air from South China based on a newly developed LC-MS/MS method. A total of 12 of the 17 emerging triazine UV filters were first positively detected in the dust and air samples. Ethylhexyl triazone (EHT) and bis-ethylhexyloxyphenol methoxyphenyl triazine (BEMT) were identified as the most abundant compounds. The median total concentrations of triazine UV filters reached 3860 ng/g in indoor dust and 1590 pg/m³ in indoor air. Gas-particle partitioning analysis showed that triazine UV filters were predominant in the particle phase in ambient air. Significant concentration correlations were observed among most triazine UV filters. The estimated daily intake of triazine UV filters through dust ingestion and air inhalation for toddlers under high-end exposure scenarios was up to 839 ng/kg bw/day, but a lack of toxic thresholds hampers accurate risk assessment. Our work highlights another emerging class of UV filters that significantly contribute to indoor chemical mixtures and expresses concerns over their occurrence and human exposure.