Indole, being the main chromophore of amino acid tryptophan and several other biologically relevant molecules like serotonin, melatonin, has prompted considerable theoretical and experimental interest. The current work focuses on the investigation of substitution effect on the ground and excited electronic states of indole using computational quantum chemistry. Having three close‐lying excited electronic states, the vibronic coupling effect becomes extremely important yet challenging for the photophysics and photochemistry of indole. Here, we have evaluated the performance of time‐dependent density functional theory against available experimental and ab initio results from the literature. The electronic effects on the excited states of indole and indole derivatives e. g. tryptophan, serotonin and melatonin are reported. A bathochromic shift has been observed in the absorption spectrum for the La state. The absorption wavelength increases in the order of indole

Small molecule activation & their transfer reactions in biological or catalytic reactions are greatly influenced by the metal-centers and the ligand frameworks. Here, we report the metal-directed nitric oxide (NO)...

1e and 3e regioselective XB formation by a free radical. 1e and 3e bond formation are realized when the free radical acts as nucleophile and electrophile, respectively, which are parametrized by electrophilicity index and chemical hardness parameters.

Electronic and vibrational spectroscopic studies of molecules are of crucial importance to characterizing a molecule and detecting the molecular species in different environments. In this review article, we summarized some important theoretical methods to calculate high-resolution electronic spectra and ro-vibrational states for small molecular systems with the inclusion of vibronic and ro-vibrational couplings, respectively. We have also reviewed a number of theoretical studies exploring some interesting organic chromophores like indole, isoalloxazine, transition metal trifluoride CoF3 and NiF3, and molecular ions like protonated rare gases and azido ions. These studies involve the calculation of spectroscopic features based on analytical potential energy surfaces constructed using high-level ab initio energies. The topology of the potential energy surfaces has been explored for these selected systems. The vibronic spectra and ro-vibrational states calculated using various theoretical methods and their comparison to available experimental results are reported in this review.

Indole, being the main chromophore of amino acid tryptophan and several other biologically relevant molecules like serotonin, melatonin, has prompted considerable theoretical and experimental interest. The current work focuses on the investigation of photophysical and photochemical properties of indole and indole derivatives e.g. tryptophan, serotonin and melatonin using theoretical and computational methodologies. Having three close-lying excited electronic states, the vibronic coupling effect becomes extremely important yet challenging for the photophysics and photochemistry of indole. Here, we have used density functional theory (DFT) extensively and evaluated the performance of DFT in compared to available experimental and ab initio results from literature. The benchmarking of the method is followed by investigation of the chemical and geometrical effects of ring substitution in indole. A bathochromic shift has been observed in the HOMO-LUMO gap as well as vertical excitation energy from indole to melatonin. While the contribution of the in-plane small adjacent groups increases the electron density of the indole ring, the out-of-plane long substituent groups have minor effect. The comparison of singlet-triplet gaps suggests highest probability of inter-system crossing for tryptophan which is in line with previous experiment. The absorption spectra calculated including the vibronic coupling are in good agreement with experiment. These results can be used to estimate the error in photophysical observables of indole derivatives calculated considering indole as prototypical system. This study also demonstrates the merits and demerits of using DFT functionals to compute the photophysical properties of indole derivatives.