Photophysical processes in multicomponent solutions composed by natural pigments, extracted from Caesalpinia echinata (Brazil-wood) leaves, are investigated. Beacuse of the main fluorescent molecules in these solutions are the chlorophyll a, chlorophyll b and pheophytin a, all features are discussed regarding these three pigments. It is observed that the fluorescence bands of these macrocyclic molecules, located around ca. 673 nm, are progressively quenched due to the increase of the solutions’ concentration. Due to a significant overlapping between their fluorescence and absorption Q-bands, it is concluded that the inner-filter effect causes such quenching. Through analysis of steady-state and time-resolved fluorescence, it is verified that the inner filter acts more effectively on the emission assigned to chlorophyll a. Invoking reported extinction coefficients for these pigments in their isolated forms, we can give a qualitative interpretation of such selectivity considering the effectiveness of the overlapping between the absorption and fluorescence bands.

Modificações no sinal de absorção de estado excitado da 5,10,15,20-tetra(4-piridil)-21H,23H-porfirina, provocadas tanto pela substituição do íon central quanto pela adição de grupos periféricos, são investigadas empregando-se pulsos laser de 5 ns com 532 nm, juntamente com medidas de absorção linear e tempo de decaimento da fluorescência. A absorção saturada reversa (RSA) aumenta consideravelmente quando os íons H+ são substituídos pelo Zn2+ na posição central do anel porfirínico. Contudo, esta diminui quando os grupos RuCl2(CO)(PPh3)2 e RuCl2(CO)(dppb) são ligados através dos anéis piridínicos às posições periféricas da porfirina, tanto para a base livre quanto para a zinco porfirina. Um modelo teórico baseado no diagrama de Jablonski foi usado para verificar qual a principal causa da diminuição do sinal de RSA provocada pelos grupos de rutênio.

Investigations on the excited state absorption signal of 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphyrin, modified by either changing the central ion or adding peripheral groups, were performed using 5 ns laser pulses at 532 nm, in association with linear absorbance and fluorescence decay time measurements. The reverse saturable absorption (RSA) increases remarkably when Zn2+ replaces H+ at the central position of the porphyrin ring. However, it decreases when RuCl2(CO)(PPh3)2 and RuCl2(CO)(dppb) groups are attached at outlying positions through the pyridine rings, for both the free base and zinc porphyrins. A theoretical model based on Jablonski diagram was used to verify the main reason for the decrease on the RSA signal caused by ruthenium groups.

Amostras de óleo obtido do fruto do Buriti (Mauritia flexuosa L.) foram caracterizadas por espectroscopia de absorção e emissão. O espectro de absorção foi obtido no intervalo de 300 a 2000 nm, enquanto o espectro de emissão foi analisado entre 400 e 800 nm, onde observamos várias bandas. Para melhor entender a complexidade destes espectros, também obtivemos os espectros de absorção e emissão dos componentes majoritários do óleo de Buriti. Correlacionando estes dados, apresentamos uma discussão sobre a origem das bandas observadas.

Oil samples obtained from Buriti (Mauritia flexuosa L.) palm tree fruits were characterized by absorption and emission spectroscopies. The absorption spectrum was recorded in the range from 300 to 2000 nm, while the emission spectrum was analyzed between 400 and 800 nm, where several bands were observed. To better understand these complex spectra, we recorded both absorption and emission spectra of its major components. By correlating these data, we present a discussion on the possible origin of the bands observed.