Flavonoids and carotenoids with rich structural diversity are ubiquitously present in the plant kingdom. Flavonoids, and especially their glycosides, are more hydrophilic than most carotenoids. The interaction of flavonoids with carotenoids occurs accordingly at water/lipid interfaces and has been found important for the functions of flavonoids as antioxidants in the water phase and especially for the function of carotenoids as antioxidants in the lipid phase. Based on real-time kinetic methods for the fast reactions between (iso)flavonoids and radicals of carotenoids, antioxidant synergism during protection of unsaturated lipids has been found to depend on: (i) the appropriate distribution of (iso)flavonoids at water/lipid interface, (ii) the difference between the oxidation potentials of (iso)flavonoid and carotenoid and, (iii) the presence of electron-withdrawing groups in the carotenoid for facile electron transfer. For some (unfavorable) combinations of (iso)flavonoids and carotenoids, antioxidant synergism is replaced by antagonism, despite large potential differences. For contact with the lipid phase, the lipid/water partition coefficient is of importance as a macroscopic property for the flavonoids, while intramolecular rotation towards coplanarity upon oxidation by the carotenoid radical cation has been identified by quantum mechanical calculations to be an important microscopic property. For carotenoids, anchoring in water/lipid interface by hydrophilic groups allow the carotenoids to serve as molecular wiring across membranes for electron transport.

To realize organic nonlinear optical (NLO) chromophores with optimized ground-state polarization and very large molecular optical nonlinearities, a novel series of heterocycle-based electronically gradient dipolar chromophores were designed and synthesized. These chromophores are featured by their same strong electron acceptor (i.e., 2-dicyanomethylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran, TCF) and the same length of π-conjugation, but different electron donors (e.g., dialkylamine and dianisylamine), different (hetero)aromatics with varying electron densities (i.e., pyrrole, thiophene, and benzene) as the auxiliary donor, and electron-poor 1,3-heteroaromatic thiazole with different regiostructures (e.g., either electron-poor C2, “matched”, or electron-rich C5, “un-matched”, is connected to the acceptor) as the auxiliary acceptor, which allows for a systematic fine-tuning of the ground-state polarization. The gradient electronic structures and optical properties of these NLO chromophores were carefully characterized by ¹H NMR, CV, UV-vis, and Hyper-Rayleigh scattering experiments. All the NLO chromophores exhibited very large static molecular first hyperpolarizabilities (β₀) in the range of 450–960 × 10⁻³⁰ esu, which showed significant dependence on the gradient electronic structures. Upon using electron-rich heteroaromatic cycle as the auxiliary donor, “matched” thiazole as the auxiliary acceptor, and/or dianisylamine as the electron donor, substantially enhanced β were obtained. Theoretical studies were carried out to understand the structure-property relationships, which showed that multiple states excitations contributed to the β values of this series of NLO chromophores. TGA investigations showed excellent thermal stability for most of the resulting NLO chromophores, with on-set temperatures for thermal decomposition higher than 250 °C. The very large β₀ values coupled with the high thermal stability indicates good application potential of this series of NLO chromophores.