  Intermolecular charge transfer reactions are key processes in physical
chemistry. The electron-transfer rates depend on a few system's parameters,
such as temperature, electromagnetic field, distance between adsorbates and,
especially, the molecular reorganization energy. This microscopic greatness is
the energetic cost to rearrange each single$-$molecule and its surrounding
environment when a charge is transferred. Reorganization energies are measured
by electrochemistry and spectroscopy techniques as well as at the
single-molecule limit using atomic force microscopy approaches, but not from
temperature$-$dependent charge transport measurements nor in a
monolithically$-$integrated molecular device. Nowadays self$-$rolling
nanomembrane (rNM) devices, with strain$-$engineered mechanical properties,
on$-$a$-$chip monolithic integration, and operable in distinct environments,
overcome those challenges. Here, we investigate the charge transfer reactions
occurring within a ca. 6 nm thick copper$-$phthalocyanine (CuPc) film employed
as electrode-spacer in a monolithically integrated nanocapacitor. Employing the
rNM technology allows us to measure the molecules' charge$-$transport
dependence on temperature for different electric fields. Thereby, the CuPc
reorganization energy is determined as (930 $\pm$ 40) meV, whereas density
functional theory (DFT) calculations support our findings with the atomistic
picture of the CuPc charge transfer reaction. Our approach presents a
consistent route towards electron transfer reaction characterization using
current$-$voltage spectroscopy and provides insight into the role of the
molecular reorganization energy when it comes to electrochemical nanodevices.
