Three-dimensional through-space/through-bond delocalization in cyclophane systems: a molecule-in-molecule approach

Electronic decoupling of a cyclophane from a metal surface

Electronic self-decoupling of an organic chromophore from a metal substrate is achieved using a naphtalenediimide cyclophane to spatially separate one chromophore unit of the cyclophane from the substrate. Observations of vibronic excitations in scanning tunneling spectra demonstrate the success of this approach. These excitations contribute a significant part of the tunneling current and give rise to clear structure in scanning tunneling microscope images. We suggest that this approach may be extended to implement molecular functions at metal surfaces.

Charge-Transfer Interactions in Organic Functional Materials

Our goal in this review is three-fold. First, we provide an overview of a number of quantum-chemical methods that can abstract charge-transfer (CT) information on the excited-state species of organic conjugated materials, which can then be exploited for the understanding and design of organic photodiodes and solar cells at the molecular level. We stress that the Composite-Molecule (CM) model is useful for evaluating the electronic excited states and excitonic couplings of the organic molecules in the solid state. We start from a simple polyene dimer as an example to illustrate how interchain separation and chain size affect the intercahin interaction and the role of the charge transfer interaction in the excited state of the polyene dimers. With the basic knowledge from analysis of the polyene system, we then study more practical organic materials such as oligophenylenevinylenes (OPV_n), oligothiophenes (OT_n), and oligophenylenes (OP_n). Finally, we apply this method to address the delocalization pathway (through-bond and/or through-space) in the lowest excited state for cyclophanes by combining the charge-transfer contributions calculated on the cyclophanes and the corresponding hypothetical molecules with tethers removed. This review represents a step forward in the understanding of the nature of the charge-transfer interactions in the excited state of organic functional materials.

Interchain interactions in organic conjugated dimers: a composite-molecule approach

A theoretical composite-molecule (CM) model is adopted for evaluating the electronic excited states and excitonic couplings of cofacial conjugated dimers where the contributions of charge-transfer (CT) exciton, unavailable by the commonly used supermolecular approach due to the inadequate basis set construction, can be unambiguously identified within this methodology. This method builds up with the basis set of individual molecules and then constructs combined electronic states for the dimer by considering intermolecular interactions including charge-transfer interactions. The dependences of the matrix elements on intermolecular distance and conjugation length are examined. At the short distance region between two of the polyene molecules in the dimer, the CT transitions are apparently mixing to both first and second excited states. Also, some of the matrix elements for the mixing of CT transitions with local transitions which related to the second excited state are found to be considerably larger than the exciton-type elements. An interesting finding is that with increasing the chain size the CT contribution to the second excited state reveals a minimum and indicates HOMO to LUMO charge transfer is not the major CT contribution to the second excited state in the face-to-face polyene dimer with larger chain size and interchain separation in the region of 3.6-4.0 A. A detail analysis reveals that HOMO-1 to LUMO and HOMO to LUMO+1 charge transfers are major CT contributions to the second excited state in the condition under study.