Dye-sensitized solar cells using a chlorophyll a derivative (PPB a der.) as the sensitizer and carotenoids having different conjugation lengths as redox spacers was studied experimentally. In this Letter, the excited state properties of the neurosporene & PPB a der. complex are investigated theoretically with quantum chemistry method. The 2D real space analysis with the transition density matrix reveals that some excited states are locally excited states, and some is the intermolecular charge transfer (ICT) state. The 3D real space analysis reveals: (1) that the orientation and the strength of the dipole moment from transition density, and (2) the orientation and result of ICT in Neurosporene & PPB a der. complex from charge difference density. (c) 2005 Elsevier B.V. All rights reserved.