Stability and reaction dynamics of trifluorinated indolylfulgides

Abstract

Quantum efficiencies and ultrafast dynamics of the ring-closure and ring-opening reaction of a trifluorinated dicyclopropyl indolylfulgide with improved photostability are investigated by stationary and ultrafast absorption spectroscopy. The ring-closure reaction occurs on the time scale of 200 fs and is found to be temperature independent (T = 287 -333 K). However, an activated behaviour is observed for the ring-opening reaction. A comparison with the corresponding nonsubstituted indolylfulgide shows that the dicyclopropyl group favours the open isomer via lower cyclisation and higher cycloreversion quantum efficiencies and faster dynamics of the ring-opening reaction.

Increasing the efficiency of the ring-opening reaction of photochromic indolylfulgides by optical pre-excitation

“…This and especially their high thermal and photochemical stability make fulgides interesting candidates for applications in molecular memories or as molecular switches [1–10]. Recent studies have shown that the ring-closure reaction of indolylfulgides is a very rapid, non-activated process with a time constant in the range between 200 – 400 fs [11–15]. In contrast, the ring-opening reaction of these molecules is slower and occurs with time constants between 2 and 20 ps [11,14–21].…”

“…Recent studies have shown that the ring-closure reaction of indolylfulgides is a very rapid, non-activated process with a time constant in the range between 200 – 400 fs [11–15]. In contrast, the ring-opening reaction of these molecules is slower and occurs with time constants between 2 and 20 ps [11,14–21]. To summarise these studies: it was found that the ring-opening reaction is thermally activated.…”

“…To summarise these studies: it was found that the ring-opening reaction is thermally activated. It becomes faster and more efficient, if thermal energy is supplied [11,20]. From these experiments it was concluded that two barriers exist in the excited state.…”

“…Furthermore the ring-opening reaction depends on illumination wavelength, chemical surrounding and substitution of the molecule [16,17]. The following reaction model has been proposed [11,21] for the ring-opening reaction (all values are given for fulgide 1 in the solvent 1,4-dioxane at room temperature without pre-excitation):…”

“…We present data from pre-excitation experiments of two fluorinated indolylfulgides [11] and one non-fluorinated indolylfulgide [23]. We will show that the increase in reaction yield differs for the three molecules and that the observations can be correlated with the specific molecular properties of the three indolylfulgides.…”