Transient kinetics of light-induced metastable states in single crystals and aqueous solutions ofNa2[Fe(CN)5NO]∙2H2O

The generation and relaxation of light-induced metastable states at room temperature is investigated in single crystals and aqueous solutions of ${\mathrm{Na}}_{2}[\mathrm{Fe}{(\mathrm{C}\mathrm{N})}_{5}\mathrm{N}\mathrm{O}]∙2{\mathrm{H}}_{2}\mathrm{O}$ (SNP), using transient absorption spectroscopy. The temporal monoexponential decay after exposure to nanosecond laser pulses results from the thermal deexcitation of the metastable state named SII. The lifetime $\ensuremath{\tau}$ of SII at $T=302\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ is $\ensuremath{\tau}=1.8(1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}\phantom{\rule{0.3em}{0ex}}\mathrm{s}$ in single crystals and $\ensuremath{\tau}=1.1(1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}\phantom{\rule{0.3em}{0ex}}\mathrm{s}$ in aqueous solutions. An Arrhenius-like behavior is verified yielding the activation energy ${E}_{A}=0.43(3)\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ and the frequency factor $Z=7\ifmmode\times\else\texttimes\fi{}{10}^{13}\phantom{\rule{0.3em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$. The buildup time of the metastable state SII is faster than $1\phantom{\rule{0.3em}{0ex}}\mathrm{ns}$ and occurs via a singlet excited state. With an exposure of $0.8\phantom{\rule{0.3em}{0ex}}\mathrm{J}∕{\mathrm{cm}}^{2}$, 0.8(2)% of the molecules can be transferred from the ground state to SII.