Synthesis and Excited-State Properties of Donor-Acceptor Azahelical Coumarins.

A set of three azahelical coumarins (s), namely, , , and , were rationally designed and synthesized, and their excited-state properties were comprehensively investigated. All three s are shown to display very high fluorosolvatochromic shifts as a result of significant intramolecular charge transfer in their excited states. The -quinoidal forms of the latter apparently contribute predominantly to large dipole moments in their excited states.

Influence of Triptycene Annulation on the Photochromism of Diphenylnaphthopyrans: Entropic Control of Thermal Reversion.

Regioisomeric naphthopyrans annulated with triptycene, i. e., Prox-NP and Dist-NP, display divergent photochromic behaviors.

One-Pot Synthesis of 4-Carboalkoxy-Substituted Benzo[]coumarins from α- and β-Naphthols and Their Excited-State Properties.

One-pot synthesis has been developed for 4-carboethoxybenzo[]coumarins starting from α-/β-naphthols. Accordingly, diverse 4-carboethoxybenzocoumarins can be synthesized in moderate-to-excellent (31-75%) isolated yields. The synthesis involves initial oxidation of naphthols to the intermediary 1,2-naphthoquinones with 2-iodoxybenzoic acid followed by a cascade of reactions, namely, Wittig olefination, Michael addition, β-elimination, and cyclization.

Coumarin-Annelated Regioisomeric Heptahelicenes: Influence of Helicity on Excited-State Properties and Chiroptical Properties.

Two regioisomeric pairs of heptahelical mono- and biscoumarins that are differentiated by "" and "" disposition of the pyran-2-one moiety have been synthesized and investigated to understand the influence of helicity on excited-state and chiroptical properties. A slight variation in the helicities is found to manifest in contrasting excited-state properties of coumarin-annelated heptahelicenes; in addition to the intramolecular charge transfer, structural relaxation in the excited state is shown from theoretical calculations to cause decrease in the fluorescence quantum yield for a system with higher helicity. The optically pure enantiomers of heptahelical coumarins exhibit helicity-dependent chiroptical properties, namely, specific rotations, molar ellipticities, Cotton effects, and anisotropic dissymmetry factors.