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Employing natural or arti cial sunscreens is essential to protect the skin from ultraviolet radiations that cause premature aging and develop melanoma and other forms of skin cancer. The 2-Phenylbenzimidazole-5-sulfonic acid, commonly known as ensulizole is a water-soluble arti cial sunscreen that absorbs mostly UV-B (280 nm − 315 nm) radiations and protects the skin against the harmful effects of these radiations. Steady-state absorption indicates a strong absorption feature at 303 nm and a weak at 316 nm that have been identi ed as π → π* and n → π* transitions, respectively. The photoluminescence (PL) spectra indicate that the PL of ensulizole is less Stokes-shifted in polar solvents and more Stokes-shifted in non-polar solvents. The average PL lifetime of ensulizole is longer in non-polar solvents as compared to polar solvents and it exhibits the shortest PL lifetime in aqueous medium that signi es its e ciency in water. This suggests in non-polar solvents intersystem crossing is the dominant mode of relaxation of the excited ππ* state. Furthermore, an increase of pH of ensulizole solution decreases the PL intensity and the lifetime.Stern-Volmer equation is employed to evaluate bimolecular quenching rate constant k q that suggests the diffusional dynamic mode of PL quenching is operative.

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Frequent exposure to ultraviolet (UV) radiation without any protection turns out to be a fatal threat to skin cancer. This can be forestalled by the direct application of sunscreen cosmetic...

Applying sunscreen on human skin provides photoprotection against the harmful ultraviolet (UV) radiation of the sun. Sunscreen absorbs UV radiations and dissipates the absorbed energy through various radiative and nonradiative pathways. The attachment of functionalized quantum dots (QDs) to the sunscreen component is a novel idea to enhance the absorption cross-section of UV radiations. Therefore, the attachment of the sunscreen component to the ligand functionalized biocompatible QDs and the absorbed energy transfer from sunscreen to the QDs could work as a model system to overall improve the efficiency of the sunscreen. This study elucidates the mechanism of size-dependent Förster resonance energy transfer (FRET) efficiency and its rate between 2phenylbenzimidazole-5-sulfonic acid (PBSA) and mercaptoacetic acid (MAA) functionalized CdS QDs. In the PBSA-QDs dyad, the PBSA (donor) dissipates UV-absorbed energy to the CdS QDs (acceptor). Following excitation at 306 nm, the steady-state photoluminescence (SSPL) and time-resolved photoluminescence (TRPL) techniques measurements demonstrate that both the nonradiative energy transfer efficiency and rate are QDs size-dependent in addition to donoracceptor distance, and suggest that bigger sized-QDs result in an increase of the FRET efficiency.

In the field of catalysis and energy applications, heterostructures of halide perovskite nanocrystals (NCs) and functionalized graphene are emerging as promising materials. In such heterostructures, it is critical to gain insights into the knowledge that governs the charge and energy transfer dynamics between the components of the heterostructures because it directly affects the efficiency of devices. In this work, we present heterostructures that consist of mercaptoacetic acid (MAA)-functionalized CsPbBr 3 NCs and alanine-functionalized graphene. The surface functionalization of CsPbBr 3 NCs and graphene enables an effective attachment of the NCs and graphene. The use of MAA as a functionalizing ligand not only passivates the surface of NCs but also provides the possibility of tuning the size of NCs and further coupling with alanine-functionalized graphene. Varying the amount of MAA allows us to synthesize the brightest CsPbBr 3 NCs with an absolute photoluminescence quantum yield (PLQY) of 49% and an emission spectral width of 25 nm. By combining alanine-functionalized graphene, the photoluminescence (PL) quenching of the NCs is observed. The photoexcited electron transfer from NCs to alanine-functionalized graphene is responsible for the occurrence of PL quenching that is advocated by time-resolved photoluminescence (TRPL) studies and cyclic voltammetry (CV) analysis. Our work provides a method to control the energetics and analyze the types of charge transfer in functionalized perovskite NCs and graphene heterostructures and motivates further research about the basic knowledge of charge transfer in functionalized donor−acceptor heterostructures.

Quantum dots (QDs) are semiconducting nanocrystals that exhibit size- and composition-dependent optical and electronic properties. Recently, Cu-based II–VI ternary Cu x Cd 1– x S (CCS) QDs have emerged as a promising class of QDs as compared to their binary counterparts (CuS and CdS). Herein, a series of ternary CCS QDs are synthesized by changing the molar concentration of Cu 2+ ions only keeping the 1:1 ratio of the stoichiometric mixture of Cd 2+ and S 2– . These CCS QDs are attached to 2-phenylbenzimidazole-5-sulfonic acid (PBSA), an eminent UV-B filter widely used in many commercial sunscreen products to avoid skin erythema and DNA mutagenic photolesions. The photoinduced Förster resonance energy transfer (FRET) is investigated from PBSA to CCS QDs as a function of Cu concentration in CCS QDs using the steady-state photoluminescence and time-resolved photoluminescence measurements. A 2-fold increase in the magnitude of non-radiative energy transfer rate ( K T ( r ) ) is observed as the molar concentration of Cu in CCS QDs increases from 2 to 10 mM. Our findings suggest that in PBSA-CCS QD dyads, the FRET occurrence from PBSA to QDs is dictated by the dynamic mode of photoluminescence (PL) quenching. The bimolecular PL quenching rate constants ( k q ) estimated by Stern–Volmer’s plots for PBSA-CCS QD dyads are of the order of 10 10 M –1 s –1 , which signifies that in the PBSA-CCS QD dyad FRET system, the process of PL quenching is entirely diffusion-controlled.