Modification of benzoindenothiophene-based organic dye with fused thiophenes for efficient dye-sensitized solar cells.

Recently low-energy-gap benzoindenothiophene (BIT)-based organic dyes have been experimentally sensitized to dye-sensitized solar cells (DSSCs) with impressive 10.9% power conversion efficiency. This paper presents a computational study of the modification of BIT-based dyes with fused thiophene moieties to build novel low band gap sensitizers. Density functional theory (DFT), tight-binding DFT, and time dependent DFT (TDDFT) approaches are used to demonstrate the electronic and optical properties of the BIT dyes and dye/(TiO2)46 complexes. Our calculations show that the structural modification by using fused thiophenes can effectively lower the band gap of the BIT dyes by 0.07-0.12 eV and affect the optical properties of BIT dyes. Enlarging the thiophene unit in BIT with thienothiophene and dithienothiophene improves the oscillator strength by 14%-25%, while the lowest-energy absorption peak basically remains at 559 nm. The incorporation of cyclopentadithiophene unit leads to a significant 47 nm red-shift of absorption peak and a 25% enhanced oscillator strength, compared to the original BIT dye. Those fused thiophenes modified BIT dyes also demonstrate ideal molecular orbital distribution patterns and ultra-fast injection time at the dye/(TiO2)46 interface. Our calculations provide useful guidance for the molecular design of novel naphthalene-based dyes for DSSC optimizations.

Design of novel conjugated microporous polymers for efficient adsorptive desulfurization of small aromatic sulfur molecules.

This paper presents a computational study of the adsorptive desulfurization of small aromatic sulfur compounds by conjugated microporous polymers (CMPs). The density-functional tight-binding method augmented with an R-6 dispersion correction is employed to investigate the physisorption binding mechanism and electronic properties of the CMP-aromatic sulfur complexes. We show that the widely extended π conjugation in the CMP skeletons is favorable for the non-covalent adsorption of aromatic thiophene and dibenzothiophene via π-π, H-π, and S-π interactions. The average binding energies are calculated to be -6.2 âˆ¼ -15.2 kcal/mol for CMP- thiophene/dibenzothiophene systems. For the dibenzothiophene molecule with larger size and more extended conjugation, it binds more than twice stronger to CMP than the thiophene molecule. We show that the replacement of quinoline unit to the phenylene group in the network linker effectively enhances the average binding capacities by around 0.8-1.8 kcal/mol. Our calculations theoretically demonstrate that CMPs materials are kind of promising candidates for the adsorptive desulfurization of small aromatic sulfur compounds. This paper provides useful theoretical guidance for design of novel carbon-based adsorbents for adsorptive desulfurization.