Structures, dipole moments and excited state lifetime of isolated 4-cyanoindole in its ground and lowest electronically excited singlet states

Abstract

The rotationally resolved electronic Stark spectrum of 4-cyanoindole and some N-D and C-D deuterated isotopologues has been measured and analyzed.

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

“…These time-dependent spectral changes must reflect the effect of solvent relaxation in the excited electronic state, as electronic transitions often induce a change in the permanent dipole moment of the chromophore in question, which consequently alters the chromophore–solvent interaction equilibrium and hence requires the surrounding solvent molecules to reposition. Indeed, a previous study has shown that the permanent dipole moment of 4-CNI is increased by ∼2.6 D (i.e., from 6.31 to 8.92 D) and its orientation is changed by ∼14° upon the transition to the lowest excited single state (i.e., 1 L a state). As shown in Figure b and Table , the TA kinetics can be well fit by a function comprising an exponential growth term and an exponential decay term with the following time constants: τ G = 9.4 ± 0.7 ps and τ D = 5.8 ± 0.5 ns (the subscripts G and D represent growth and decay, respectively).…”

Explicit Projection of Stokes Shifts onto Solvent Motion in an Aqueous Liquid and Linear Response Theory

“…The failure is attributed to the significant volume change on the solute created by the electron transfer process, leading to a substantial structure change of the solvent. , Similarly, in our previous probe on tryptophan in the protein Staphylococcus nuclease, the amino acid side chains presented a different structural alignment between the ground and excited states, which resulted in the disagreement of the ground-state LR . Even for tryptophan in an aqueous liquid, the significantly different bond lengths between the La state and the ground state, − which are not included in conventional MD simulations, might cause the geometry change of the nearby solvent and lead to the inappropriate usage of LR.…”

Tryptophan as a Template for Development of Visible Fluorescent Amino Acids

“…In addition, the permanent dipole moment of the S 1 state of 4CN-indole was determined to be 9.60 D, which is ca. 3.2 D larger than that of the ground electronic state . This difference explains why 4CN-indole exhibits a large Stokes shift in water.…”

“…For example, Matsika and Abou-Hatab et al 55 have shown, using high level quantum mechanical calculations, that the brighter (fluorescent) state of 4CN-indole is the 1 L b state in aqueous solution, whereas in the gas phase the 1 L a state is responsible for both the absorption and emission of 4CN-indole. Similarly, Schmitt and co-workers 56,57 have studied the electronic transition properties of 4CN-indole, using both experimental and theoretical methods, and concluded that unlike most other indole derivatives, the lowest excited singlet (S 1 ) state of 4CN-indole in the gas phase is mainly 1 L a -character and the corresponding transition dipole moment runs through positions 1 and 4 (Figure 8). A similar conclusion was also reached for indole-4-carboxylic acid (4CO 2 H-indole) by Plusquellic and co-workers.…”

“…3.2 D larger than that of the ground electronic state. 57 This difference explains why 4CN-indole exhibits a large Stokes shift in water.…”