A DFT Study of the Low-Lying Singlet Excited States of the All-Trans Peridinin in vacuo

Riccardo Spezia, Costantino Zazza, Amedeo Palma, Andrea Amadei, and Massimiliano Aschi*

Dipartimento di Chimica, Universita` di Roma "La Sapienza", P.le Aldo Moro 5, 00185 Roma, Italy, and De'partment de Chimie, CNRS UMR 8640 PASTEUR, Ecole Normale Supe'rieure, 24 rue Lhomond, 75231 Paris Cedex 05, France, Consorzio interuniversitario per le Applicazioni di Supercalcolo Per Universita` e Ricerca (CASPUR), via dei Tizii 6b, 00185 Roma, Italy, Istituto per lo Studio dei Materiali Nanostrutturati (CNR-ISMN), via Salaria, Km 29.3, 00016 Monterotondo S. (Roma), Italy, Dipartimento di Scienze e Tecnologie Chimiche, Universita` di Roma "Tor Vergata", via della Ricerca Scientifica 1, 00133 Roma, Italy, and Dipartimento di Chimica, Ingegneria Chimica e Materiali, Universita` de l'Aquila, via Vetoio (Coppito 1), 67010 l'Aquila, Italy

Received: January 27, 2004. In Final Form: June 4, 2004

FULL TEXT

Abstract

The electronic properties of peridinin (Per) are investigated using density functional theory (DFT) with a time dependent (TD) treatment for transitions from the ground state to the low-lying electronic excited states. The use of a TD-DFT approach was first tested on the simpler -carotene molecule in order to see the performances of different functionals. It turns out from the present study that a TD-DFT approach provides a rather good qualitative picture for the electronic properties of this system for which the use of highly correlated ab initio methods with the needed prescriptions, for example, a large enough basis set and/or active space, is still prevented by its large dimension. The vertical transitions of Per obtained in vacuo using TD-DFT are in good agreement with experimental data available in a nonpolar solvent like n-hexane. Vertical energies obtained for the minimum energy structure of Per were also refined, spanning the Per in vacuo conformational space using ab initio molecular dynamics on its ground state hypersurface. These calculations also confirm the reliability of TD-DFT calculations at least on properties available from a dynamical sampling, that is, possible state inversion and partial explanation of bandwidth. Hence, combining these results with TD-DFT calculations, it is possible to better understand some spectroscopic properties of peridinin.