Convergent Synthesis of New Types of Stabilized Carotenoid Compounds (Report‪)‬

INTRODUCTION Carotenoids play three important roles in plant and bacterial photosynthesis as a light-harvesting pigment, a photoprotective agent, and a structural stabilizing element. The red to yellow pigments absorb visible light in the green to blue wavelength region (400~550 nm) complementary to chlorophyll, and thus transfer energy to the photosynthetic reaction center [1]. Carotenoids also protect the photosynthetic apparatus by reversibly quenching the hazardous singlet oxygen and the chlorophyll triplet state [2]. The structural stabilizing effect of carotenoids was postulated by the [pi]-stacking interactions of the polyenes with the porphyrins of chlorophylls within van der Waals distances [3]. There have been extensive studies to elucidate the modified carotenoid molecules containing electro-active polar end groups as electronic devices for intramolecular charge transfer, electro-chromic, semiconducting, or nonlinear optical properties [4]. The synthesis of these modified carotenoids 1a-d has been based on the reaction of the natural crocetin dialdehyde 2 with the Wittig salts of the polar end groups, which restricted not only the structures but also the properties of these potential molecular wires (Scheme 1).