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Lipid molecules are involved in a wide range of fundamental cell functions, explaining the enormous structural diversity of lipids, partly due to the large number of different fatty acids, which can vary in length and in the number and position of unsaturated bond(s). Interestingly, imbalances between (un)saturated species have been reported in various pathologies. Hence, it is of particular importance to study in detail the structural consequences associated with variations in the nature of the lipid hydrocarbon tails. To this end, 17 single‐component lipid bilayers, varying only in the nature of the hydrocarbon core are studied by molecular dynamics (MD) simulations. The structural analysis reveals that the effect of the nature of the two fatty acids on the overall membrane structure is additive. In addition, TDDFT quantum mechanical (QM) calculations are performed to study the modulations of the nonlinear optical (NLO) properties of an embedded probe, serving as local structural microscopes. However, these calculations highlight the difficulty of rationalizing changes in the NLO responses, in relation with the nature of the hydrocarbon region of the host environment. Nevertheless, less dense and packed membranes, which allow the probe to adopt more planar conformations, are associated with larger NLO responses. [ABSTRACT FROM AUTHOR]

The nonlinear optical (NLO) properties of a double photochrome molecular switch are reported for the first time by considering the four trans forms of a dithienylethene-indolinooxazolidine hybrid. The four forms are characterized by means of hyper-Rayleigh scattering (HRS) experiments and quantum chemical calculations. Experimental measurements provide evidence that the pH- and light-triggered transformations between the different forms of the hybrid are accompanied by large variations of the first hyperpolarizability, which makes this compound an effective multistate NLO switch. Quantum chemical calculations conducted at the time-dependent Hartree-Fock and time-dependent DFT levels agree with the experimental data and allow a complete rationalization of the NLO responses of the different forms. The HRS signal of the forms with an open indolinooxazolidine moiety are more than one order of magnitude larger than that measured for the other forms, whereas the open/closed status of the dithienylethene subunit barely influences the dynamic NLO properties. However, extrapolation of the NLO responses to the static limit leads to univocally distinguishable intrinsic responses for three of the various forms. This hybrid system thus acts as a highly efficient multistate NLO switch for eventual exploitation in optical memory systems with multiple storage and nondestructive readout capacity. [ABSTRACT FROM AUTHOR]

Merocyanine dyes that exhibit antithetic cyanine-like behaviour and giant first-order hyperpolarisability ( β) values have been designed. These cyanine-type dyes open up an intriguing route towards molecular-based electro-optic materials as well as new second-harmonic generation dyes for imaging. [ABSTRACT FROM AUTHOR]