Series expansion of a scalable Hermitian excitonic renormalization method.

Utilizing the sparsity of the electronic structure problem, fragmentation methods have been researched for decades with great success, pushing the limits of ab initio quantum chemistry ever further. Recently, this set of methods has been expanded to include a fundamentally different approach called excitonic renormalization, providing promising initial results. It builds a supersystem Hamiltonian in a second-quantized-like representation from transition-density tensors of isolated fragments, contracted with biorthogonalized molecular integrals.

Searching the chemical space of hetero-atom bridged norbornadienes.

The efficient utilization of solar energy as renewable source is a central pillar of societal future energy production. So-called molecular solar thermal energy storage (MOST) systems have attracted considerable attention as storage solution and heat release on demand. Substituted norbornadiene/quadricyclane (NBD/QC) derivatives have been shown to be well suited for this task, in particular when substituted with electron donating and accepting functional groups.

Meta-Connected Oligo-Azobenzenes Outperform Their Para Counterparts.

Systems with multiple photoswitchable units in one molecule have attracted considerable attention in the past years as they are useful for a broad variety of possible applications. Especially, linked azobenzenes sharing one benzene ring are of high interest since their direct linkage introduces an additional photoswitchable unit at only small increase in molecular weight. In this spirit, linear oligo-azobenzenes had been synthesized, though their photochemical properties have only been investigated for short chain lengths.

Diels-Alder Reactivity of Triisopropylsilyl Ethynyl Substituted Acenes.

We investigated the Diels-Alder reaction of 6,13-bis(triisopropylsilylethynyl)pentacene (1) with small dienophiles such as (bridged) dihydronaphthalenes/cyclohexenes that yielded adducts at the central ring, the other dienophiles predominantly or exclusively attacked the unsubstituted off-center ring. The difference in regioselectivity was investigated by DFT calculations. Apart from dispersion interactions, it is due to the steric demand of the dienophiles, which need to fit in between the silylethynyl substituents to react at the central ring.

Breaking Strong Alkynyl-Phenyl Bonds: Poly(-phenylene ethynylene)s under Mechanical Stress.

Stronger chemical bonds withstand higher mechanical forces; thus, the rupture of single bonds is preferred over the rupture of double or triple bonds or aromatic rings. We investigated bond scission in poly(dialkyl--phenylene ethynylene)s (PPEs), a fully conjugated polymer. In a scale-bridging approach using electron-paramagnetic resonance spectroscopy and gel permeation chromatography of cryomilled samples, in combination with density functional theory calculations and coarse-grained simulations, we conclude that mechanical force cleaves the sp-sp bond of PPEs (bond dissociation energy as high as 600 kJ mol).