Controlling S2 Population in Cyanine Dyes Using Shaped Femtosecond Pulses

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• 作者：Muath Nairat ; Arkaprabha Konar ; Vadim V. Lozovoy ; Warren F. Beck ; G. J. Blanchard ; Marcos Dantus
• 刊名：Journal of Physical Chemistry A
• 出版年：2016
• 出版时间：March 24, 2016
• 年：2016
• 卷：120
• 期：11
• 页码：1876-1885
• 全文大小：639K
• ISSN：1520-5215

文摘

Fast population transfer from higher to lower excited states occurs via internal conversion (IC) and is the basis of Kasha’s rule, which states that spontaneous emission takes place from the lowest excited state of the same multiplicity. Photonic control over IC is of interest because it would allow direct influence over intramolecular nonradiative decay processes occurring in condensed phase. Here we tracked the S₂ and S₁ fluorescence yield for different cyanine dyes in solution as a function of linear chirp. For the cyanine dyes with polar solvation response IR144 and meso-piperidine substituted IR806, increased S₂ emission was observed when using transform limited pulses, whereas chirped pulses led to increased S₁ emission. The nonpolar solvated cyanine IR806, on the other hand, did not show S₂ emission. A theoretical model, based on a nonperturbative solution of the equation of motion for the density matrix, is offered to explain and simulate the anomalous chirp dependence. Our findings, which depend on pulse properties beyond peak intensity, offer a photonic method to control S₂ population thereby opening the door for the exploration of photochemical processes initiated from higher excited states.