Enumerating Intramolecular Charge Transfer in Conjugated Organic Compounds

Charge
transfer across conjugated organic molecules is the functional
basis of many optoelectronic and semiconductor devices. The ability
to design such molecules to suit a given device application is highly
desirable; yet, realizing this prospect is impeded by the lack of
an algorithm that quantifies the extent of intramolecular charge transfer
(ICT) in absolute terms. In turn, an algorithm to describe ICT is
held back by a poor definition of one of its key dependent terms:
conjugation. Current equations assume that π-bonding operates
solely across two bonds, even though conjugation extends beyond these
limits, and such equations only yield relative measures of π-conjugation.
This work presents a four-step algorithm that enumerates ICT on an
absolute scale. The method is applied successfully to four types of
optoelectronic materials; results demonstrate the need to reconsider
certain fundamental chemical-bonding and ICT concepts for conjugated
molecules. These findings have implications for all optoelectronic
and semiconducting materials.