  Charge-transfer excitons possessing long radiative lifetime and net permanent
dipole moment are highly appealing for quantum dot (QD) based energy harvesting
and photodetecting devices, in which the efficiency of charge separation after
photo-excitation limits the device performance. Herein, using a hybrid
time-dependent density functional theory, we have demonstrated that the
prevailing rule of selecting materials with staggered type-II band alignment
for realization of charge-transfer exciton breaks down in epitaxially fused QD
molecules. The excitonic many-body effects are found to be significant and
distinct depending on the exciton nature, causing unexpected reverse ordering
of exciton states. Strikingly, twisting QD molecule appears as an effective
means of modulating the orbital spatial localization towards charge separation
that is mandatory for a charge-transfer exciton. Meanwhile, it manifests the
intra-energy-level splitting that counterbalances the distinct many-body
effects felt by excitons of different nature, thus ensuring the successful
generation of energetically favourable charge-transfer exciton in both
homodimer and heterodimer QD molecules. Our study extends the realm of
twistroincs into zero-dimensional materials, and provides a genuine route of
manipulating the exciton nature in QD molecules.
