Energy Gap between the Poly‑<i>p</i>‑phenylene Bridge and Donor Groups Controls the Hole Delocalization in Donor–Bridge–Donor Wires
Denan Wang
Marat R. Talipov
Maxim V. Ivanov
Rajendra Rathore
10.1021/jacs.6b09209.s003
https://acs.figshare.com/articles/journal_contribution/Energy_Gap_between_the_Poly_i_p_i_phenylene_Bridge_and_Donor_Groups_Controls_the_Hole_Delocalization_in_Donor_Bridge_Donor_Wires/4289981
Poly-<i>p</i>-phenylene wires are critically important
as charge-transfer materials in photovoltaics. A comparative analysis
of a series of poly-<i>p</i>-phenylene (<sup><i><b>R</b></i></sup><b>PP</b><sub><i><b>n</b></i></sub>) wires, capped with isoalkyl (<sup><i><b>iA</b></i></sup><b>PP</b><sub><i><b>n</b></i></sub>), alkoxy (<sup><i><b>RO</b></i></sup><b>PP</b><sub><i><b>n</b></i></sub>), and dialkylamino
(<sup><i><b>R2N</b></i></sup><b>PP</b><sub><i><b>n</b></i></sub>) groups, shows unexpected evolution
of oxidation potentials, i.e., decrease (−260 mV) for <sup><i><b>iA</b></i></sup><b>PP</b><sub><i><b>n</b></i></sub>, while increase for <sup><i><b>RO</b></i></sup><b>PP</b><sub><i><b>n</b></i></sub> (+100 mV) and <sup><i><b>R2N</b></i></sup><b>PP</b><sub><i><b>n</b></i></sub> (+350
mV) with increasing number of <i>p</i>-phenylenes. Moreover,
redox/optical properties and DFT calculations of <sup><i><b>R2N</b></i></sup><b>PP</b><sub><i><b>n</b></i></sub>/<sup><i><b>R2N</b></i></sup><b>PP</b><sub><i><b>n</b></i></sub><sup>+•</sup> further show that the symmetric bell-shaped hole distribution distorts
and shifts toward one end of the molecule with only 4 <i>p</i>-phenylenes in <sup><i><b>R2N</b></i></sup><b>PP</b><sub><i><b>n</b></i></sub><sup>+•</sup>, while shifting of the hole occurs with 6 and 8 <i>p</i>-phenylenes in <sup><i><b>RO</b></i></sup><b>PP</b><sub><i><b>n</b></i></sub><sup>+•</sup> and <sup><i><b>iA</b></i></sup><b>PP</b><sub><i><b>n</b></i></sub><sup>+•</sup>, respectively.
Availability of accurate experimental data on highly electron-rich
dialkylamino-capped <sup><i><b>R2N</b></i></sup><b>PP</b><sub><i><b>n</b></i></sub> together with <sup><i><b>RO</b></i></sup><b>PP</b><sub><i><b>n</b></i></sub> and <sup><i><b>iA</b></i></sup><b>PP</b><sub><i><b>n</b></i></sub> allowed
us to demonstrate, using our recently developed Marcus-based multistate
model (MSM), that an increase of oxidation potentials in <sup><i><b>R2N</b></i></sup><b>PP</b><sub><i><b>n</b></i></sub> arises due to an interplay between the electronic
coupling (<i>H</i><sub>ab</sub>) and energy difference between
the end-capped groups and bridging phenylenes (Δε). A
comparison of the three series of <sup><i><b>R</b></i></sup><b>PP</b><sub><i><b>n</b></i></sub> with
varied Δε further demonstrates that decrease/increase/no
change in oxidation energies of <sup><i><b>R</b></i></sup><b>PP</b><sub><i><b>n</b></i></sub> can
be predicted based on the energy gap Δε and coupling <i>H</i><sub>ab</sub>, i.e., decrease if Δε < <i>H</i><sub>ab</sub> (i.e., <sup><i><b>iA</b></i></sup><b>PP</b><sub><i><b>n</b></i></sub>),
increase if Δε > <i>H</i><sub>ab</sub> (i.e., <sup><i><b>R2N</b></i></sup><b>PP</b><sub><i><b>n</b></i></sub>), and minimal change if Δε
≈ <i>H</i><sub>ab</sub> (i.e., <sup><i><b>RO</b></i></sup><b>PP</b><sub><i><b>n</b></i></sub>). MSM also reproduces the switching of the nature
of electronic transition in higher homologues of <sup><i><b>R2N</b></i></sup><b>PP</b><sub><i><b>n</b></i></sub><sup>+•</sup> (<i>n</i> ≥
4). These findings will aid in the development of improved models
for charge-transfer dynamics in donor–bridge–acceptor
systems.
2016-11-23 00:00:00
Marcus-based multistate model
R PP n
iA PP n
R 2N PP n
electron-rich dialkylamino-capped R 2N PP n
RO PP n
Donor Groups Controls
oxidation potentials
bell-shaped hole distribution
DFT
MSM
energy gap Δε
H ab