The deexcitation of the S<SUB>1</SUB> state of aminoanthraquinones: a steadystate and timeresolved study

The non-radiative processes of deactivation from the lowest singlet excited state of aminoanthraquinones have been studied using steady-state and time-resolved methods. The fluorescence decay rate constant, kf correlates well with the solvent polarity parameter, ET(30), in nonhydrogen bonding solvents. Large deuterium isotope effects in fluorescence lifetimes (&#964;f) and quantum yields (&#934;f) are observed in the case of 1-amino (AAQ) and 1-methylaminoanthraquinones (MAQ), where the S1 state is mainly deactivated through internal conversion to the ground state. The temperature-dependence of the fluorescence quantum yields of various aminoanthraquinones was also investigated. The &#934;f and &#964;f exhibited strong temperature-dependence in the case of 1-acetylaminoanthraquinone (ACAQ). In the case of ACAQ, the intersystem crossing to the triplet state is a major deactivation channel from the S1 and in this derivative a close-lying T2 state seems to be responsible for the high kisc rate. The fluorescence properties of 1,5-diaminoanthraquinone (DAQ) are affected by intermolecular hydrogen bonding with alcohols. Increasingn-alkyl chain length in the case of l-(n-alkyl)aminoanthraquinones from methyl to butyl does not produce any change in the fluorescence properties, whereas a hydroxypropyl substitution results in a small decrease of &#934;f and &#964;f in these compounds, indicating an interaction of the hydroxyl group with the carbonyl group of the aminoanthraquinones

Studies of the triplet state properties of 1,5- diaminoanthraquinone using laser flash photolysis

The triplet-triplet absorption spectrum of 1,5-diaminoanthraquinone is reported in methanol, together with triplet lifetimes in various solvents. The triplet lifetimes in linear alcohols correlate well with the solvent polarity parameter ET(30) of the alcohols. The transient spectrum of 1,5-diaminoanthraquinone in deuterated ethanol is broader than the spectrum in ethanol. The triplet lifetime of the deuterated species is twice that observed in ethanol

The non-radiative processes from the S<SUB>1</SUB> state of aminoanthraquinones: a steady state and time-resolved study

The non-radiative processes of deactivation from the lowest singlet excited state of aminoanthraquinones have been studied using steady state and time-resolved methods. The fluorescence decay rate constant kf correlates well with the solvent polarity parameter ET(30) in non-hydrogen-bonding solvents. Large deuterium isotope effects in fluorescence lifetimes &#964;f and quantum yields &#966;f are observed in the case of 1-amino and 1-methylamino anthraquinones, where the S1 state is mainly deactivated through internal conversion to the ground state. The temperature dependence of the fluorescence quantum yields of various aminoanthraquinones was also investigated. &#966;f and &#964;f exhibited strong temperature dependences in the case of 1-acetylaminoanthraquinone. In the case of 1-acetylaminoan-thraquinone, intersystem crossing to the triplet state is a major deactivation channel from the S1 and in this derivative a close-lying T2 state seems to be responsible for the high kisc rate

Nile red and DCM fluorescence Anisotropy studies in C12E7/DPPC mixed systems

The lipid/surfactant mixed interactions between the lipid dipalmitoylphosphatydilcholine (DPPC) and the non-ionic surfactant C12E7 [C12H25(OCH2CH2)7OH] were studied by the use of fluorescence anisotropy of Nile Red and DCM laser dye. Three different regions, consisting of mixed micelles, mixed vesicles and both aggregates, were identified. Nile Red fluorescence anisotropy is wavelength dependent, the spectra being decomposed in two log-normal functions. These results are consistent with a solvent relaxation process, with distinct anisotropies for the relaxed and unrelaxed states. The spectral properties (anisotropy and maximum emission wavelength) of the relaxed state show higher sensitivity to the environment than those of the unrelaxed state. DCM fluorescence anisotropy show similar trends. This was interpreted as a result of a trans-cis photoisomerization process. The observed anisotropy spectrum was decomposed in two gaussian functions, reflecting a distinct anisotropy for each isomer.Fundação para a Ciência e a Tecnologia (FCT) - Projecto POCTI/32901/FIS/99