Excited state structure of isolated 2-cyanoindole and the binary 2-cyanoindole-(H2O)1 cluster from a combined Franck-Condon and rotational constants fit

Photoenhancement of the C≡N Stretching Vibration Intensity of Aromatic Nitriles

“…This hypothesis is based on the notion that upon electronic excitation, the cyano moiety, which is a strong electron-withdrawing group (EWG), tends to facilitate (partial) charge migration within the aromatic ring(s), leading to lengthening of the CN bond. For example, Schmitt and co-workers − have shown, for several cyanoindoles, including 2-cyanoindole (2-CNI), 4-cyanoindole (4-CNI), and 5-cyanoindole (5-CNI), that the CN bond in the S 1 state is longer than that in the S 0 state and the C–C bond connecting the cyano group and the indole ring is shortened. Such a photoexcitation-induced electronic structure change is expected not only to shift ν CN to lower wavenumbers but also to significantly increase the magnitude of ε CN .…”

Excited state hydrogen or proton transfer pathways in microsolvated n-cyanoindole fluorescent probes

“…Experimental information exists for monohydrated indole, 2-CNI, 3-CNI, and for mono and dihydrated 5-CNI. 42,69–71 Our calculations predict that the character is the same in the mono and dihydrated systems, i.e. one additional water does not change the character.…”

“…Both experiment and theory have demonstrated that this is the case for the addition of one water molecule to isolated n -CNI with respect to indole, 2-CNI, 3-CNI, and 5-CNI. 69–71 In 5-CNI 71 it is also found that addition of a second water molecule also retains the character of L a . For 2-CNI and 3-CNI their fluorescence properties are not sensitive to the amount of water solvent.…”

“…3,41 These systems have an L b minimum isolated, monohydrated and in bulk solvent. 3,41,69,70 In the case of the 4-, 6-, and 7-CNI-(H 2 O) m clusters, no experimental studies have been done that characterize the S 1 minimum in solution or with water clusters. For these systems we rely on previous and current theoretical calculations to establish the character of the minimum.…”

“…Experimental measurements of the induced dipole moment using Stark effect for isolated indole and indole-(H 2 O) 1 cluster have reported that fluorescence occurs from the non-polar excited L b state. 42 Similarly, combined Franck-Condon and rotational constants fitting of 2-CNI-(H 2 O) 1 cluster 69 and rotationally resolved electronic spectroscopy of 3-CNI-(H 2 O) 1 cluster 70 reported that they emit from the L b state. Mass-selected resonant two-photon ionization (R2PI) and UV-UV hole-burning, of jet cooled 5-CNI and 3-CNI and their water clusters, were also measured.…”