title: Energy Gap between the Poly-p-phenylene Bridge and Donor Groups Controls the Hole Delocalization in Donor-Bridge-Donor Wires.
abstract: Poly-p-phenylene wires are critically important as charge-transfer materials in photovoltaics. A comparative analysis of a series of poly-p-phenylene (RPPn) wires, capped with isoalkyl (iAPPn), alkoxy (ROPPn), and dialkylamino (R2NPPn) groups, shows unexpected evolution of oxidation potentials, i.e., decrease (-260 mV) foriAPPn, while increase forROPPn(+100 mV) andR2NPPn(+350 mV) with increasing number of p-phenylenes. Moreover, redox/optical properties and DFT calculations ofR2NPPn/R2NPPn+•further show that the symmetric bell-shaped hole distribution distorts and shifts toward one end of the molecule with only 4 p-phenylenes inR2NPPn+•, while shifting of the hole occurs with 6 and 8 p-phenylenes inROPPn+•andiAPPn+•, respectively. Availability of accurate experimental data on highly electron-rich dialkylamino-cappedR2NPPntogether withROPPnandiAPPnallowed us to demonstrate, using our recently developed Marcus-based multistate model (MSM), that an increase of oxidation potentials inR2NPPnarises due to an interplay between the electronic coupling (Hab) and energy difference between the end-capped groups and bridging phenylenes (Δε). A comparison of the three series ofRPPnwith varied Δε further demonstrates that decrease/increase/no change in oxidation energies ofRPPncan be predicted based on the energy gap Δε and coupling Hab, i.e., decrease if Δε < Hab(i.e.,iAPPn), increase if Δε > Hab(i.e.,R2NPPn), and minimal change if Δε ≈ Hab(i.e.,ROPPn). MSM also reproduces the switching of the nature of electronic transition in higher homologues ofR2NPPn+•(n ≥ 4). These findings will aid in the development of improved models for charge-transfer dynamics in donor-bridge-acceptor systems.
authors.affiliation: Department of Chemistry, Marquette University , P.O. Box 1881, Milwaukee, Wisconsin 53201-1881, United States.
authors.forename: Denan
authors.initials: D
authors.lastname: Wang
authors.affiliation: Department of Chemistry, Marquette University , P.O. Box 1881, Milwaukee, Wisconsin 53201-1881, United States.
authors.forename: Marat R
authors.identifier: 0000-0002-7559-9666
authors.initials: MR
authors.lastname: Talipov
authors.affiliation: Department of Chemistry, Marquette University , P.O. Box 1881, Milwaukee, Wisconsin 53201-1881, United States.
authors.forename: Maxim V
authors.identifier: 0000-0002-6171-9524
authors.initials: MV
authors.lastname: Ivanov
authors.affiliation: Department of Chemistry, Marquette University , P.O. Box 1881, Milwaukee, Wisconsin 53201-1881, United States.
authors.forename: Rajendra
authors.identifier: 0000-0001-7387-7936
authors.initials: R
authors.lastname: Rathore