Computation of the acetone ultraviolet spectrum in gas phase and in aqueous solution by a mixed discrete/continuum model

The ultraviolet spectrum of acetone in vacuum and in aqueous solution has been computed by different quantum mechanical methods coupled to the polarizable continuum model (PCM) for describing bulk solvent effects. The results in vacuo show that the time-dependent density functional theory (TDDFT) approach using the PBEO functional reproduces quite well the result obtained at the CASPT2 level. Supermolecule computations confirm that water molecules belonging to the first shell of polar groups (here the carbonyl oxygen) must be explicitly included in the quantum mechanical treatment, whereas the effect of other solvent molecules (which is far from being negligible) can be reliably described by the PCM. Moreover, statistical averaging effects have been taken into account by performing canonical molecular dynamics (MD) simulations followed by TDDFT quantum mechanical computations on representative clusters of increasing dimensions immersed in a polarizable continuum. The results show that the combined MD/DFT/PCM approach is reliable and effective, although the performances of the force field used in the MD simulations must be further investigated.     

1H-INDENYLFURAN AND THIOPHENE DERIVATIVES– A NEW CLASS OF SINGLET OXYGEN SENSITIZERS

Abstract— Photophysical and photochemical properties of 1H-indenylfuran and thiophene derivatives were studied. UV spectra showed that all the compounds tested absorbed UV light in the region 350–380 nm. The fluorescence spectra of 4a-e showed bands in the region 410–470 nm and quantum yields (φ_F) in the range 0.25–0.88. Attempts to calculate the triplet energy of 4a-e failed except for 4c and 4d , which showed E_T= 43–44 kcal mol^-1. These compounds are a new class of singlet oxygen sensitizers. The sensitized reaction of 2,5-dimethylfuran with singlet oxygen was followed showing that 4a and 4e are more reactive than α-terthiophene (4.0 and 2.5 times respectively), while the other compounds show the same reactivity as 1 . This behavior can be explained considering the different intersystem crossing quantum yields of compounds 4a-e . Diazabicyclo[2. 2. 2]octane is a quencher of singlet oxygen in this reaction, while we can exclude superoxide ion formation using the photooxidation of α, α-dimethylstilbene.