Rotationally resolved electronic spectroscopy of 3-cyanoindole and the 3-cyanoindole–water complex

Abstract

The rotationally resolved electronic spectra of the origin bands of 3-cyanoindole, 3-cyanoindole(d₁), and the 3-cyanoindole–(H₂O)₁ cluster have been measured and analyzed using evolutionary algorithms. For the monomer, permanent dipole moments of 5.90 D for the ground state, and of 5.35 D for the lowest excited singlet state have been obtained from electronic Stark spectroscopy. The orientation of the transition dipole moment is that of an ¹L_b state for the monomer. The water moiety in the water cluster could be determined to be trans-linearly bound to the NH group of 3-cyanoindole, with an NH⋯O hydrogen bond length of 201.9 pm in the electronic ground state. Like the 3-cyanoindole monomer, the 3-cyanoindole–water cluster also shows an ¹L_b-like excited singlet state. The excited state lifetime of isolate 3-cyanoindole in the gas phase has been determined to be 9.8 ns, and that of 3-cyanoindole(d₁) has been found to be 14.8 ns, while that of the 1 : 1 water cluster is considerably shorter (3.6 ns). The excited state lifetime of 3-cyanoindole(d₁) in D₂O solution has been found to be smaller than 20 ps.