Comparison of methods for calculating the properties of intramolecular hydrogen bonds. Excited state proton transfer

Abstract

A series of molecules related to malonaldehyde, containing an intramolecular H-bond, are used as the testbed for a variety of levels of ab initio calculation. Of particular interest are the excitation energies of the first set of valence excited states, n* and *, both singlet and triplet, as well as the energetics of proton transfer in each state. Taking coupled cluster results as a point of reference, configuration interaction-singles-second-order Møller-Plesset ͑CIS-MP2͒ excitation energies are too large, as are CIS to a lesser extent, although these approaches successfully reproduce the order of the various states. The same may be said of complete active space self-consistent-field ͑CASSCF͒, which is surprisingly sensitive to the particular choice of orbitals included in the active space. Complete active space-second-order perturbation theory ͑CASPT2͒ excitation energies are rather close to coupled cluster singles and doubles ͑CCSD͒, as are density functional theory ͑DFT͒ values. CASSCF proton transfer barriers are large overestimates; the same is true of CIS to a lesser extent. MP2, CASPT2, and DFT barriers are closer to coupled cluster results, although yielding slight underestimates.

Ultrafast Excited-State Proton Transfer of 2-(2‘-Hydroxyphenyl)benzothiazole: Theoretical Analysis of the Skeletal Deformations and the Active Vibrational Modes

“…481 S ring (66). 528 514 δ CO (36), S ring (15), R ON (7) 534 Ph ring (25), δ CO (17), R ON (6) 566 Ph ring (30) 630 ring def a Wave packet motion from ref . b Frequencies CIS/6-31G* scaled by 0.9. c Notation for the internal coordinates and PED description.…”

Theoretical studies of conjugation and substituent effect on intramolecular proton transfer in the ground and excited states

“…However, the large size of the systems is still precluded an advanced theoretical characterization (CASSCF, CCSD and CASPT2) of the potential energy surfaces of ESIPT. Fortunately, the recent calculations [14,27] showed that TDDFT can reliably predict the potential energy surface of ESIPT. In this work, we constructed the potential energy surface (PES) of ESIPT by TD [28] (B3LYP)/6-31G(d,p) theoretical calculations for the B3LYP/6-31G(d,p) ground state optimized structures.…”

Tautomerism: Introduction, History, and Recent Developments in Experimental and Theoretical Methods

“…Even apart from the question of whether it is just the barrier heights that are needed to estimate the tunneling frequencies -this idea probably derives from Arrhenius and the transition-state theory, but in tunneling other parameters are also relevant -no consensus can be found between various methods to calculate these. Kar et al [83] reported a comparison of a number of calculations where the barrier heights in the ground state vary from −1.8 kcal mol −1 (not a barrier at all) to +20.2 kcal mol −1 . In the excited states, this is even worse.…”