Excited state properties of acceptor-substitute carotenoids: 2D and 3D real-space analysis Mengtao Sun a, * , Pa ¨r Kjellberg a , Fengcai Ma b , To ˜ nu Pullerits a a Department of Chemical Physics, Lund University, Box 124, Lund SE22100, Lund, Sweden b Department of Physics, Liaoning University, Shenyang 110036, China Received 4 September 2004; in final form 10 November 2004 Available online 15 December 2004 Abstract Excited state properties of three (neutral, weak and strong) acceptor-substitute carotenoids (b-carotene) are studied theoretically with the methods of two-dimensional (2D) and three-dimensional (3D) real-space analysis. The influences of different (neutral, weak and strong) function groups attached to the polyene chain to the excited state property of the carotenoids are discussed. By the 3D real-space analysis, the charge and energy transfer of the three acceptor-substitute carotenoids after vertical absorption are studied with the transition density and charge difference density. By the 2D real-space analysis, the electron–hole coherences and excitation delocalization of the three acceptor-substitute carotenoids are studied with the transition density matrix. Ó 2004 Elsevier B.V. All rights reserved. 1. Introduction Carotenoids are ubiquitous in plants, animals and bacteria. Light harvesting by carotenoids is a fundamen- tal part of the earliest reaction in photosynthesis [1–3]. Light energy that is absorbed by carotenoids is rapidly and efficiently transferred to the chlorophylls, thereby allowing photosynthesis to harvest energy over a wider range of wavelengths than would be possible with chlo- rophyll alone [4]. The excited state properties of the carotrnoids are largely determined by their polyene backbone and the functional groups attached to the polyene chain, and play an important role in the func- tional photochemistry of photosynthetic organisms [1–3]. Experimentally, photosynthetic light harvesting by carotenoids [4], photophysical properties of carote- noids [3,5], third-order optical nonlinearities in polar- ized carotenoids [6], ultrafast carotenoid band shifts upon excitation of nearby bacteriochlorophyll [7], and the carotenoid-to-chlorophyll energy transfer [2,8–10] have attracted intense interest and been studied. Theo- retically, the excited state properties of the carotenoids [11–14] and intermolecular hydrogen bonding between carotenoid and bacteriochlorophyll in LH2 [15] were studied. Recently, several elaborate theoretical ap- proaches have been used to inspect visually all molecular orbital contributing to the excitation for large conju- gated carotenoids and polymers. One is the 2D real- space analysis of transition density matrix, representing the electronic transition between the ground state and the electronically excited state [16–19], which is used to analyze the electron–hole coherence and the excitation deodorization of conjugated molecule. Another one is the 3D real-space analysis of transition density and charge difference density [20–22], which has been used to analyze the charge and energy transfer in several con- jugated polymers. The different (neutral, weak and strong acceptor) functional groups influence strongly the ground and excited state properties of cartenoids [1–3,6,11–14]. For example, the strong acceptors increase extent of intramolecular charge transfer (ICT) from the polyenic chain to the acceptor moiety in the ground state [6]. 0009-2614/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.cplett.2004.11.074 * Corresponding author. E-mail address: mengtao.sun@chemphys.lu.se (M. Sun). www.elsevier.com/locate/cplett Chemical Physics Letters 401 (2005) 558–564