We investigate the photoexcited states in potassium-tetracyanoquinodimethane (K-TCNQ) crystals using the first and second intramolecular charge excitations of the $\mathrm{TCN}{\mathrm{Q}}^{-}$ molecule. Infrared-light reflection measurements with these excitations reveal a photoinduced phase transition (PIPT) from the spin-Peierls to the Mott insulating phase. Femtosecond time-resolved photoluminescence and visible-light reflection measurements are used to investigate the origin of the PIPT. Our results show that the PIPT triggered by the first intramolecular charge excitation occurs via the relaxation to charge transfer excited state as proposed previously, while the PIPT by the second intramolecular charge excitation is caused by electron emission. It is expected that this mechanism will be effective in other charge transfer complexes.

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• Electron emission
• Photoinduced effect
• 1-dimensional spin chains
• Organic compounds
• Femtosecond laser spectroscopy
• Reflectivity
• Time-resolved photoluminescence