Computational Chemistry & Theoratical Molecular Physics
External Funding

Computational Chemistry & Theoretical Molecular Physics

Molecular orbital assistance in the design of intramolecular and photoinduced electron transfer systems

Conventional DFT and TDDFT implementations are not very successful when applied to charge-transfer states. For photoinduced electron transfer the excited absorbing state is in resonance with the charge-transfer state

A great deal of insight can be gained for charge-transfer systems from simple molecular orbital energy diagrams of the separate donor and acceptor moieties  and this can be of great value for nano-hybrids where quantitative information on the charge-transfer states is still an impossible task.

Example1:  a PET sensor for OP nerve agents
In terms of orbital diagrams the photoinduced charge transfer (or electron transfer) is indicated by the existence of degeneracy between the D→D* and D→A*  excitations: (I. D. Petsalakis et al.  J. Mol. Struct. (THEOCHEM) 867 (2008) 64

Figure 2: Orbital levels for the tertiary amine-pyrene sensor

A theoretical approach has been proposed  for the design of donor-acceptor ICT systems and for photoinduced electron transfer (PET) hybrids of fullerene, based on orbital level diagrams of the separate donor and acceptor moieties.  , (I. D. Petsalakis and G. Theodorakopoulos, Chemical Physics Letters 525–526 (2012) 105–109)

Minimization of the HOMO-LUMO gap in ICT systems translates to a requirement for near degeneracy of the HOMO of the donor and LUMO of the acceptor

Figure 3. Orbital level diagram for the TCBD-TTF model system

Similarly, near degeneracy of the LUMO of the donor and LUMO of the acceptor indicates the possibility of PET in the combined hybrid

Figure4: Orbital energies of CN-substituted pyrene and comparison with the levels of C60 fullerene







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