Vibronic Approaches to the Calculation of Optical Chiral Spectra

Vibronic Approaches to the Calculation of Optical Chiral Spectra Fabrizio Santoro1 1 Consiglio Nazionale delle Ricerche-CNR, Istituto di Chimica dei Composti Organometallici, Area della Ricerca del CNR, Via Moruzzi 1, I-56124 Pisa, Italy Abstract In recent years we developed time-independent (TI) and time-dependent (TD) approaches to simulate the lineshapes of electronic spectra of large molecules, computing the associated vibronic structures[1] . Here we illustrate their application to a number of chiroptical spectroscopies including electronic circular dichroism (ECD), circularly polarized luminescence (CPL), and magnetic circular dichroism (MCD). In particular we show how these computations can help to determine the dominant conformers of large chiral pyridocyclophanes [2], to explain the difference in the lineshapes of absorption and ECD and in emission and CPL of a series of substituted helicenes [3], and to understand the origin of the change of sign in the ECD spectra of chirally substituted benzenes [4]. In order to simulate the ECD vibronic shapes of exciton coupled dimers, we recently proposed a non-adiabatic method based on a rigorous definition of effective modes and on wavepacket quantum dynamics on the coupled electronic potential energy surfaces. Here we present this approach showing that it delivers spectra in nice agreement with experiment both in covalently bound dimers [5] and in polythiophenes aggregates. Finally, we briefly discuss possible hybrid quantum-classical protocols for the computation of electronic spectra in systems exhibiting conformers with markedly different chiroptical response. These methods are useful when the interconversion barriers are too low to allow a simple treatment in terms of the separate contribution of each conformer. References [1] Santoro F, Barone V. Computational approach to the study of the lineshape of absorption and electronic circular dichroism spectra Int. J. Quantum. Chem 2010;110:624-636 [2] Padula D, Lahoz I R, Díaz C, Hernández F E, Di Bari L, Rizzo A, Santoro F Magdalena Cid, M A combined experimental-computational investigation to uncover the puzzling behaviour of chiral pyridocyclophanes: chiroptical response and one- and two-photon absorption, Chemistry submitted [3] Liu Y, Lin N, Longhi G, Abbate S, Santoro F. Vibronic calculations of the electronic circular Dichroism and circularly polarized luminescence of substituted helicenes In preparation [4] Pescitelli G, Barone V, Di Bari L, Rizzo A, Santoro F. Vibronic coupling dominates the electronic circular dichroism of the benzene chromophore 1Lb band J. Org. Chem. 2013;78:7398-7405. [5] Padula D, Picconi D, Lami A, Pescitelli G, Santoro F. Electronic circular dichroism in exciton-coupled dimers: vibronic spectra from a general all-coordinates quantum-dynamical approach J. Phys. Chem. A 2013;117:3355-3368