  We present a detailed study of charge transfer (CT) excited states for a
large number of structural conformations in a light-harvesting
Carotenoid-diaryl-Porphyrin-C60 (CPC60) molecular triad. The molecular triad
undergoes a photoinduced charge transfer process exhibiting a large excited
state dipole moment, making it suitable for application to molecular-scale
opto-electronic devices. An important consideration is that the conformational
flexibility of the CPC 60 triad impacts its dynamics in solvents. Since
experimentally measured dipole moments for the triad of ~110 Debye (D) and ~160
Debye strongly indicate a range in conformational variability for the triad in
the excited state, studying the effect of conformational changes on the CT
excited state energetics furthers the understanding of its charge transfer
states. We have calculated the lowest CT excited state energies for a series of
14 triad conformers, where the structural conformations were generated by
incrementally scanning a 360 degree torsional (dihedral) twist at the
C60-porhyrin linkage and the porphyrin-carotenoid linkage. Additionally, five
different CPC60 conformations were studied to determine the effect of
pi-conjugation and particle-hole Coulombic attraction on the CT excitation
energies. Our calculations show that structural conformational changes in the
triad show a variation of ~0.4 eV in CT excited state energies in the
gas-phase. The corresponding calculated excited state dipoles show a range of
88 D - 188 D.
