Investigation of ground and excited state photophysical properties of gadolinium phthalocyanine
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- 作者：Marcelo G. Vivas ; Leonardo de Boni ; Luciana Gaffo ; Cleber R. Mendonca
- 关键词：Gadolinium phthalocyanine ; Excited state absorption ; Femtosecond wavelength-tunable Z-scan technique ; Pulse train fluorescence technique ; Rate equation model ; Transition dipole moments
- 刊名：Dyes and Pigments
- 出版年：February, 2014
- 年：2014
- 卷：101
- 期：Complete
- 页码：338-343
- 全文大小：578 K
文摘
In this present work, we investigated the singlet excited state absorption (ESA) spectrum and intersystem crossing dynamics of gadolinium phthalocyanine (GdPc) in toluene. For that, we employed the femtosecond wavelength-tunable Z-scan and picosecond Pulse Train Fluorescence (PTF) techniques to determine, respectively, the singlet ESA cross-section on a wide spectral range (from 460 up to 740聽nm) and the intersystem crossing time (singlet-triplet transition). We observed that the ESA spectrum presents distinct absorption behaviors, i.e., saturable (SA) and reverse saturable absorption (RSA). We have also been able to identify regions in which the excited state absorption cross-section has the same magnitude as the ground state one (at 600 and 720聽nm). The RSA effect was observed for wavelengths shorter than 600聽nm and longer than 720聽nm, while SA occurs in the Q-band region, located between 600 and 720聽nm. To describe the main singlet-singlet transitions, we measured the fluorescence decay time and employed a rate equation model considering a three-energy-level-diagram. Ratios between excited and ground state absorption cross-section from 0.4 to 4 were observed along the ESA spectrum. From these results, we calculated the transition dipole moment between the excited states for the main electronic transitions of GdPc. To obtain the intersystem crossing time, we incorporated an additional level in our model and used the PTF technique to probe the population transfer to the triplet state. Our results pointed out that the intersystem crossing time is higher than 300聽ns, which corresponds to a maximum triplet quantum yield of 1.5%.