Fluorescently labeled amphiphilic polybetaines have been prepared, and their dilute solution properties in water, chloroform, methanol, and mixed organic solvents have been investigated by fluorescence spectroscopy, dynamic light scattering, and 1 H NMR spectroscopy. The copolymer chains consisted of N-isopropylacrylamide and N-phosphorylcholine-N′-ethylenedioxybis(ethyl)acrylamide units in ∼1/1 molar ratio, as well as from 3 to 10 mol % hydrophobic units, such as N-n-(octadecyl)acrylamide, N-(1H,1H-perfluoro-n-octyl)acrylamide, or N-[(1-pyrenyl)-4-butyl]-N-(n-octadecyl)acrylamide. In water, the polybetaines associate in multichain aggregates ranging in size from 170 to 220 nm. The assembly of the polymers in water is triggered by two cumulative effects: (1) hydrophobic interactions between the hydrocarbon or fluorocarbon chains and (2) ion pair formation between the phosphorylcholine groups. The polymers do not associate in methanol, but chain aggregation occurs in chloroform, where the phosphorylcholine groups form clusters stabilized by water structuration around these highly polar groups.

The excited states of UV-B absorbers, ethylhexyl triazone (EHT) and diethylhexylbutamido triazone (DBT), have been studied through measurements of UV absorption, fluorescence, phosphorescence, triplet-triplet absorption and electron paramagnetic resonance spectra in ethanol. The energy levels of the lowest excited singlet (S1) and triplet (T1) states and quantum yields of fluorescence and phosphorescence of EHT and DBT were determined. In ethanol at 77 K, the deactivation process of EHT and DBT is predominantly fluorescence, however, a significant portion of the S1 molecules undergoes intersystem crossing to the T1 state. The observed phosphorescence spectra, T1 lifetimes and zero-field splitting parameters suggest that the T1 state of EHT can be assigned to a locally excited (3)ππ* state within p-(N-methylamino)benzoic acid, while the T1 state of DBT can be assigned to a locally excited (3)ππ* state within p-(N-methylamino)benzoic acid or p-amino-N-methylbenzamide. The quantum yields of singlet oxygen generation by EHT and DBT were determined by time-resolved near-IR phosphorescence measurements in ethanol at room temperature. EHT and DBT did not exhibit significantly antioxidative properties by quenching singlet oxygen, in contrast to the study by Lhiaubet-Vallet et al.

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The lowest excited triplet (T1) state of the most widely used UV-B absorber, octyl methoxycinnamate (OMC), has been studied through measurements of phosphorescence and electron paramagnetic resonance spectra in rigid solutions at 77 K. The energy level and lifetime of the T1 state of OMC were determined. The observed T1 lifetime and zero-field splitting parameter suggest that OMC possesses mainly a 3ππ* character in the T1 state.

Dioctyl 4-methoxybenzylidenemalonate (DOMBM) is an effective stabilizer for photolabile 4-tert-butyl-4'-methoxydibenzoylmethane (BMDBM). DOMBM is superior to the most widely used UV-B absorber, octyl methoxycinnamate (OMC), at preserving its UV-B absorbance in the presence of BMDBM. The energy levels of the lowest excited singlet (S(1)) and triplet (T(1)) states of DOMBM were determined by measuring fluorescence and phosphorescence spectra in ethanol at 77 K. The energy level of the T(1) state of DOMBM is lower than that of BMDBM and is higher than that of OMC. The triplet-triplet energy transfer from BMDBM to DOMBM was demonstrated by measuring the electron paramagnetic resonance (EPR) and time-resolved phosphorescence spectra. The phosphorescence and EPR signals of DOMBM are too weak to be observed through the direct excitation in ethanol at 77 K. The phosphorescence spectrum was observed by using external heavy atom effects of ethyl iodide. The EPR spectrum was observed by using benzophenone as a triplet sensitizer. The fluorescence quantum yield of DOMBM is small in ethanol at room temperature. Only the fast component, due to the heat released from the excited state of DOMBM, was observed in the time-resolved thermal lensing experiments at room temperature. These results show that the quantum yield of the S(1) → T(1) intersystem crossing is negligible and the deactivation process is predominantly internal conversion to the ground state for DOMBM.