Rotationally Resolved UV Spectroscopy of the Rotamers of Indole-4-Carboxylic Acid: Evidence of Charge Transfer Quenching
John Yi, Sergio Romero Servin, Leonardo Alvarez Valtierra, David F. Plusquellic
Rotationally resolved electronic spectra of two conformational isomers of jet-cooled Indole-4-Carboxylic Acid (I4CA) and the deuterated forms of the acid (COOD) and amide (N-D) groups have been obtained using a UV laser/molecular beam spectrometer. The in-plane orientation of the acid group defines the two lowest energy rotamers of I4CA. The S1←S0 origin bands of the two rotamers and four isotopologues have been fit to asymmetric rotor Hamiltonians in both electronic states. From the best-fit parameters, the positions of the H-atoms in the principle axis frames of each conformer are determined and serve to unambiguously identify the syn forms (i.e., COHO) of the cis and trans rotamers. The experimental S0 and S1 inertial parameters, hydrogen atom positions and transition dipole moment (TDM) orientations are compared with the results of theoretical calculations. The TDM orientation indicates the S1 state is the 1La state in contrast to most substituted indoles. The molecular orbital properties and natural charges are investigated to better understand the 1La/1Lb state reversal and the extent of intramolecular charge transfer that impacts the rotamer-dependent fluorescence lifetimes.
, Romero, S.
, Alvarez, L.
and Plusquellic, D.
Rotationally Resolved UV Spectroscopy of the Rotamers of Indole-4-Carboxylic Acid: Evidence of Charge Transfer Quenching, The Journal of Chemical Physics, [online], https://doi.org/10.1063/5.0003140
(Accessed September 21, 2021)