We assess how the utilization of different DFT functionals for obtaining the equilibrium geometries and vibrational frequencies affect the description of the thermochemistry and subsequent calculation of the optical properties of a dihydroazulene-vinylheptafulvene photoswitch. The assessment covers nine popular DFT functionals (BLYP, B3LYP, CAM-B3LYP, M06-L, M06, M06-2X, PBE, PBE0, and ωB97X-D) in conjugation with five different Pople style basis sets (6-31+G(d), 6-31++G(d,p), 6-311+G(d), 6-311++G(d,p), and 6-311++G(3df,3pd)). It is identified that only CAM-B3LYP, M06-2X, and PBE0 are able to quantitatively describe the correct trends in the thermochemical properties. The subsequent calculation of the optical properties using the CAM-B3LYP functional shows that there is little difference in whether the CAM-B3LYP, M06-2X, or PBE0 functionals have been used to calculate the equilibrium geometries. Utilizing the identified functionals, we investigate how the number of electron withdrawing cyano substituents influence the thermochemistry and optical properties of the molecular photoswitch.
We have investigated the effects of substituents on the properties of the dihydroazulene/vinylheptafulvene photoswitch. The focus is on the changes of the thermochemical properties by placing electron withdrawing and donating groups on the monocyano and dicyano structures of the parent dihydroazulene and vinylheptafulvene compounds. We wish to increase the energy storage capacity, that is, the energy difference between the dihydroazulene and vinylheptafulvene isomers, of the photoswitch by computational molecular design and have performed over 9000 electronic structure calculations using density functional theory. Based on these calculations, we obtain design rules for how to increase the energy storage capacity of the photoswitch. Furthermore, we have investigated how the activation energy for the thermally induced vinylheptafulvene to dihydroazulene conversion depends on the substitution pattern, and based on these results, we have outlined molecular design considerations for obtaining new desired target structures exhibiting long energy storage times. Selected candidate systems have also been investigated in terms of optical properties to elucidate how sensitive the absorption maxima are to the functionalizations.
The construction of open-system diabatic Hamiltonians relevant for the investigation of electron transfer processes is a computational challenge. Here all relevant parameters for Redfield propagations are extracted from ab initio computations.
Boron subphthalocyanines (SubPcs) are attractive as light harvesting materials in photovoltaic devices. Here we present the synthesis, optical and electrochemical properties, and device performances of a series of donor−acceptor‐functionalized SubPc derivatives incorporating a carboxylic acid for anchoring onto TiO2. Liquid‐ and solid‐state dye‐sensitized solar cells (DSCs) were prepared from three compounds, and a triad system consisting of two aniline donor moieties and a benzothiadiazole acceptor moiety was found to exhibit the highest power conversion efficiency (PCE) in the series (PCE=1.54 %; solid‐state device). The compounds were prepared by stepwise acetylenic coupling reactions. In addition, we present the synthesis and optical properties of a SubPc derivative incorporating three anilino‐substituted 1,1,4,4‐tetracyanobutadiene units, prepared by the [2+2] cycloaddition between three ethynyl units at the SubPc periphery and three tetracyanoethylene molecules followed by electrocyclic ring‐opening reactions.
Scheme 1. Rhodamine monomers and dimers and equilibria between closedand open isomers. All derivatives were obtained from R575 as precursor
Communications
Boron subphthalocyanines comprised of three isoindole units bridged by aza-linkages are attractive light harvesters on account of their intense low-energy absorptions. Herein, we present a class of related compounds, in which one or two isoindole units are substituted for thieno[3,4-c]pyrrole units - thieno-fused subporphyrazines. Such changes have remarkable consequences for the optical properties, as was revealed by combined experimental and theoretical studies. Thus, we find that the lowest-energy absorptions cover a much broader region with a significantly redshifted end-absorption and without compromising the absorption intensities. Thieno-fused subporphyrazines also underwent more readily oxidation and reduction, indicating an increased HOMO energy and decreased LUMO energy. In addition, they were found to readily co-crystallize with Buckminsterfullerene, C . Altogether, these findings render this new class of chromophores attractive candidates for light-harvesting applications.
Tweezer-like molecules comprised of two boron subphthalocyanine (SubPc) units were prepared by Sonogashira couplings and investigated using NMR spectroscopy for their ability to bind fullerenes (C and C). The preorganization of the tweezers provided association constants of ca. 10 M in toluene- d, while a SubPc monomer did not show any association. Nevertheless, the SubPc monomer crystallized with the fullerenes as 2:1 complexes, supporting the favorable tweezer-like design for complexation, which was further corroborated by computations.
Graphyne allotropes of carbon are fascinating materials, and their electronic properties are predicted to rival those of the “wonder material” graphene. One allotrope of graphyne, having rectangular symmetry rather than hexagonal, stands out as particularly attractive, namely 6,6,12-graphyne. It is currently an insurmountable challenge, however, to design and execute a synthesis of this material. Herein, we present synthesis and electronic properties of molecules that serve as model compounds. These oligomers, so-called radiaannulenes, are prepared by iterative acetylenic coupling reactions. Systematic optical and redox studies indicate the effective conjugation length of the radiaannulene oligomers is nearly met by the length of the trimer. The HOMO-LUMO gap suggested by the series of oligomers is still, however, higher than that expected for 6,6,12-graphyne from theory, which predicts two nonequivalent distorted Dirac cones (no band gap). Thus, the radiaannulene oligomers present a suitable length in one dimension of a sheet, but should be expanded in the second dimension to provide a unique representation of 6,6,12-graphyne.
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