Ultrafast Dynamics of Room Temperature Ionic Liquids after Ultraviolet Femtosecond Excitation

• Published in: The journal of physical chemistry. B 2007-05, Vol.111 (18), p.4830-4836
• Main Authors: Brands, H, Chandrasekhar, N, Unterreiner, A.-N
• Format: Article
• Language: English
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp067163f

The photochemistry and relaxation dynamics of four room-temperature ionic liquids (RTILs) after ultraviolet (UV) photolysis were investigated by femtosecond pump−probe absorption spectroscopy. A pulse duration-limited rise of the induced absorption in halide-containing RTILs at various probe wavelengths was attributed to the generation of solvated electrons. With continuous irradiation (static conditions), di- and trihalide ion formation became apparent especially below 1000 nm. The formation of trihalide ions was further confirmed by steady-state UV absorption spectroscopy. All RTILs showed a rich photochemistry after UV photolysis leading to the build-up of various long-lived intermediate products as evidenced from the observation that ionic liquids turn yellow upon continuous irradiation. On the other hand, exposing RTILs to the excitation pulse for a short time (rapid-scan method) significantly suppressed the formation of halides. The results suggest that the development of flow-cell systems for highly viscous ionic liquids is urgently needed to quantitatively investigate their ultrafast dynamics.