A series of functionalized 6-alkoxy phenalenones was prepared through an unprecedented oxidative dealkylation of readily available phenalene precursors. The starting phenalenes were efficiently synthesized via an aminocatalyzed annulation/O-alkylation strategy starting from simple substrates. The spectroscopic properties of some phenalenones were investigated in different solvents. Introducing an alkoxy substituent at the 6-position onto the phenalenone framework results in a redshift of the absorption. The synthesized phenalenones exhibit low fluorescence quantum yields and the fluorescence decay was studied in different solvents highlighting the presence of several lifetimes. The singlet oxygen ( 1 O 2 ) photosensitizing propensity of some phenalenones was investigated and the results showed the striking importance of the phenalenone molecular structure in generating singlet oxygen with high yields. The ability of phenalenones to generate singlet oxygen was then harnessed in three photooxygenation AUTHOR INFORMATION
The reaction of 2,5-dibromopyrazine with N-Lithium pyrazolate in a 1:2 ratio leads to a mixture of 2-bromo-5-(1H-pyrazol-1-yl)pyrazine (I) and 2,5-di(1H-pyrazol-1-yl)pyrazine (II). The structures of I and II are highly planar. Two absorption bands can be observed for the compounds in the UV-Vis region, having ε in the order of 10 m cm . TD-DFT computed results support the nature of the lower energy absorptions as π →π* transitions, including an additional intraligand charge transfer transition for I (π →π* ). Upon excitation at 280 or 320 nm, the emission of both compounds is almost not affected by solvent polarity or oxygen presence, showing two bands for I and one for II in the 350-450 nm region. Emission of II follows a mono-exponential decay, while I decays following a bi-exponential law, hypothesized from π →π* and π →π* transitions. Photodegradation of I and II follows a first-order kinetic with constants of 1.18 × 10 min and 0.13 × 10 min , respectively. Results suggest that photodegradation of I starts with the loose of bromide followed by intermolecular pyrazolyl subtraction and ring opening. This path is not available for II, which is reflected in its enhanced photostability.
We synthesized an anthracene derivative with solvatochromic properties to be used as a molecular probe for membrane dynamics and supramolecular organization.
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