Photophysical properties of lumichromes in water

The photophysics of lumichrome, 1-methyllumichrome, and lumiflavin in water solutions have been investigated. Fluorescence lifetimes of 2.7 and 2.2 ns were observed for lumichrome and 1-methyllumichrome, respectively, the corresponding triplet state lifetimes of 17 and 18 μs have been obtained from the transient absorption spectra. Evidence for long lived species with absorption maxima near 450 nm and lifetimes of ca. 400 μs has been found in the transient absorption spectra of both lumichromes. Quantum yields for the sensitised production of singlet oxygen, φ_Δ, are 0.36 and 0.41 for lumichrome and 1-methyllumichrome, respectively, in D₂O.     

Readily Available Fluorescence Probes for Zinc Ion in Aqueous Solution of Neutral pH

Zinc ion in aqueous solution of neutral pH was detected by a probe that is readily obtained by simply mixing commercially available cyclen (a Zn(II) receptor) and lumazine or lumichrome (a heterocyclic fluorophore containing an imide moiety as partial structure) in an equal molar ratio. The initially generated cyclen-Zn(II) complex interacts with lumazine to form a cyclen-Zn(II)-lumazine complex whereby the intensity of fluorescence is enhanced. These Zn(II) probes showed excellent selectivity for Zn(II) over other divalent metal ions such as Pb(II), Cu(II), Co(II), Ni(II), and good selectivity over Cd(II). The X-ray crystal structure of the cyclen-Zn(II)-lumazine complex revealed that the cyclen-chelated Zn(II) binds deprotonated lumazine at the N-1.     

Spectroscopy and photophysics of dimethyl-substituted alloxazines

We have calculated the electronic structure and absorption spectra from the ground state and the first triplet excited state for five dimethylalloxazines, using the TD-DFT approach. The results of the calculations were correlated to experimental spectral and photophysical data, including the transient spectra reported here containing triplet–triplet absorption data, using the proximity effect theory to explain the variations of the ISC rates with the substitution pattern and solvent. Additionally, singlet oxygen yields were measured for these compounds, demonstrating their high efficiency as singlet oxygen photosensitizers.