mmetry breaking charge transfer and charge separation
(SBCT and SBCS) are processes in which a pair of identical
chromophores (dimer) absorb a photon and use its energy to
transfer an electron from one chromophore to the other,
breaking the symmetry of the chromophore in the dimer.0–00
This excited state phenomenon is rationalized to occur in the
photosynthetic reaction center enabling the efficient formation
of charge-separated states that are ultimately utilized in the
synthesis of adenine triphosphate (ATP).00 The concept of SBCT
and SBCS has also been successfully exploited for developing
photocatalytic and photovoltaic systems operating with
minimal energy loss.00,00 Also, it has been successfully employed
in light-to-electricity converting optoelectronic devices.00,00 In
symmetric molecular dimers, upon photoexcitation, the weakly
coupled dimers form an excited state that dynamically localizes
on one of the chromophore units of the dimer, rapidly
producing a localized excited state (LE). Fluctuations in the
local solvent environment surrounding the dimer create an
asymmetry in the two units and are mainly responsible for
driving charge transfer (SBCT) and solvent-stabilized charge
separation (SBCS) with the radical cation and radical ion
species. This mechanism of producing radical pairs is different
from the asymmetric donor–acceptor (D–A) systems where the
electron (or hole) transfer is energetically dictated to be
a vectorial process producing Dc
+
–Ac
− species through differences in redox potentials. Experimentally, the emission properties of the charge transfer state produced in the dimer are
used to distinguish SBCT and SBCS. SBCT is oen an emissive
state, while SBCS is known to produce charge-separated states
decaying nonradiatively. In SBCS the electron and holes are
fully decoupled and behave independently while in SBCT electron–hole pairs are weakly coupled, oen referred to as charge
transfer excitons.0–00