Environmentally Friendly Sunscreens: Mechanochemical Synthesis and Characterization of β-CD Inclusion Complexes of Avobenzone and Octinoxate with Improved Photostability

We report on the mechanochemical synthesis of inclusion complexes obtained by reacting β-cyclodextrin (β-CD) with two widely used sunscreens, namely, avobenzone (AVO) and octinoxate (OCT). Formation of crystalline inclusion complexes was confirmed via a combination of solid-state techniques, including X-ray diffraction (XRD), Raman, and ATR-FTIR spectroscopies. A new, metastable polymorph of avobenzone was also isolated and characterized. NMR spectroscopy and thermal analyses (TGA and DSC) allowed us to evaluate the host/guest ratio and the water content (ca. 8H2O) in crystalline (β-CD)2·AVO and (β-CD)3·OCT2. Photodegradation of the two sunscreens upon inclusion in the hydrophobic cavity of β-CD was evaluated in solution via mass spectrometry (ESI-MS) and UV-vis spectroscopy and found to be sharply reduced. All findings indicate that the inclusion of AVO and OCT in β-CD might represent a viable route for the preparation of environmentally friendly sunscreens with improved photostability to be used in formulations of sun creams

Assembling photoactive materials from polycyclic aromatic hydrocarbons (PAHs): room temperature phosphorescence and excimer-emission in co-crystals with 1,4-diiodotetrafluorobenzene

Co-crystallization between the polycyclic aromatic hydrocarbons anthracene (A) and 9-methylanthracene (MA) with 1,4-diiodotetrafluorobenzene (I2F4) afforded three novel co-crystals, viz. A·(I2F4)2 and an unexpectedly complex system with two distinct compositions, namely MA·I2F4 and (MA)4·I2F4, which can be mechanochemically interconverted by a change in the stoichiometry of the reactive mixtures. Interestingly, all co-crystals are dual-emissive materials and exhibit different mechanisms of emission. A·(I2F4)2 and MA·I2F4 fluoresce from isolated molecules, whereas the luminescence of (MA)4·I2F4 is dominated by excimer emission. In all cases, phosphorescence at RT (RTP) is observed and interpreted as a direct consequence of the interactions between the iodine atoms of the I2F4 co-former and the π-electron density of the anthracene aromatic rings. Furthermore, [4 + 4] photoactivity within (MA)4·I2F4 was also investigated by means of FTIR/NMR spectroscopy and PXRD. The photophysical and photochemical behaviors of all solids are discussed and rationalized based on their structural features