No abstract

We have investigated eleven density functionals, including LDA, PBE, mPWPW91, TPSS, B3LYP, X3LYP, PBE0, O3LYP, B97-1, MPW1K, and TPSSh, for their performances on describing hydrogen bond (HB) interactions. The emphasis has been laid not only on their abilities to calculate the intermolecular hydrogen bonding energies but also on their performances in predicting the relative energies of intermolecular H-bonded complexes and the conformer stabilities due to intramolecular hydrogen bondings. As compared to the best theoretical values, we found that although PBE and PBE0 gave the best estimation of HB strengths, they might fail to predict the correct order of relative HB energies, which might lead to a wrong prediction of the global minimum for different conformers. TPSS and TPSSh did not always improve over PBE and PBE0. B3LYP was found to underestimate the intermolecular HB strengths but was among the best performers in calculating the relative HB energies. We showed here that X3LYP and B97-1 were able to give good values for both absolute HB strengths and relative HB energies, making these functionals good candidates for HB description.

The performance of donor–acceptor (D–A) conjugated polymer-based photocatalyts for solar hydrogen production is severely limited by poor charge mobility and weak reactive sites. Here, a series of D–A conjugated polymers with electronegative fluorine atoms on the backbone is presented and the influence of fluorination on charge transfer and catalytic site activity is investigated. Theoretical calculation reveals that sequential fluorination on the A unit benzothiadiazole will activate the catalytic site, and the photocatalytic H2 generation process could be illustrated by a proton-coupled electron-transfer mechanism. Two series of fluorinated polymers were synthesized, and accelerated charge transfer was also verified. Among them, linear B-FOBT-1,4-E and porous B-FOBT-1,3,5-E with simultaneous electron-donating CH3O– and electron-withdrawing F-substitution show a H2 evolution rate that is 3.1 and 28.8 times higher than that of nonfluorinated counterparts, respectively, and the apparent quantum yield of 5.7% at 420 nm is obtained for B-FOBT-1,4-E. The results provide reciprocal understanding of the activation nature of substituent-regulating polymers.