Excited state intramolecular proton transfer in 1-(trifluoroacetylamino)naphthaquinone: a CASPT2//CASSCF computational study

Abstract

The excited state intramolecular proton transfer (ESIPT) in 1-(trifluoroacetylamino)-naphthaquinone (TFNQ) has been investigated using the CASSCF and CASPT2 computational approaches with the 6-31G(d) basis set. The structures and relative energies of critical points along the proton transfer reaction coordinate were optimized and the associated spectroscopic and electrostatic properties obtained. Combined quantum mechanical and molecular mechanical (QM/MM) Monte Carlo simulations were performed to elucidate solvent effects on the vertical excitation S₀ → S₁. It was found that the ESIPT reaction is a barrierless process that takes place on a very flat potential energy surface (PES) and the tautomeric structure of the reaction product is the only minimum on the excited state surface. The PES for both the ground and excited state from accurate electronic structure calcualtions will be used to parameterize empirical force fields in subsequent molecular dynamics simulations of the reaction in solution.

† This paper is dedicated to Professor Michael Robb on the occasion of his 60th birthday.

Supporting Information: Excited State Intramolecular Proton Transfer in 1-(trifluoroacetylamino)anthraquinone: a CASPT2//CASSCF Computational Study

Alessandro Cembran and Jiali Gao

Department of Chemistry, University of Minnesota, Minneapolis, MN 55455, USA

The geometries for the optimized structures are reported, together with the ESP charges for S₀ and S₁ for each structure.

Table

Figure S1. Radial distribution function for the transferred proton and the TIP4P water oxygen.

Acknowledgements

The authors thank the National Institutes of Health for partial support of this research.

Notes

† This paper is dedicated to Professor Michael Robb on the occasion of his 60th birthday.

† From reference 47, for a broadband excitation, the oscillator strength f can be related to the molar extinction coefficient ε by the formula:

in which the integral runs over the band shape and is the frequency in cm⁻¹. From reference 3 we can estimate an absorption band width of 8000 cm⁻¹. By describing the band as a Gaussian function with an α value of 3 × 10⁻⁷ (which makes the function decay to zero around ±4000 cm⁻¹) and integrating, it turns out that f should be around 0.085.