Building block (chemistry) | EPFL Graph Search

Building block is a term in chemistry which is used to describe a virtual molecular fragment or a real chemical compound the molecules of which possess reactive functional groups. Building blocks are used for bottom-up modular assembly of molecular architectures: nano-particles, metal-organic frameworks, organic molecular constructs, supra-molecular complexes. Using building blocks ensures strict control of what a final compound or a (supra)molecular construct will be. Building blocks for medicinal chemistry In medicinal chemistry, the term defines either imaginable, virtual molecular fragments or chemical reagents from which drugs or drug candidates might be constructed or synthetically prepared. Virtual building blocks Virtual building blocks are used in drug discovery for drug design and virtual screening, addressing the desire to have controllable molecular morphologies that interact with biological targets. Of special interest for this purpose are the buil

FB-REDA: fragment-based decomposition analysis of the reorganization energy for organic semiconductors

Kun-Han Lin

We present a fragment-based decomposition analysis tool (FB-REDA) for the reorganisation energy (lambda). This tool delivers insights on how to rationally design low-lambda organic semiconductors. The contribution of the fragment vibrational modes to the reorganization energy is exploited to identity the individual contributions of the molecular building blocks. The usefulness of the approach is demonstrated by offering three strategies to reduce the reorganization energy of a promising dopant-free hole transport material (TPA1PM, lambda = 213 meV). A reduction of nearly 50% (TPD3PM, lambda = 108 meV) is achieved. The proposed design principles are likely transferable to other organic semiconductors exploiting common molecular building blocks.

ROYAL SOC CHEMISTRY2020

Rational Design of Hole Transport Materials: Tools and Structure-Packing-Property Relationships

Kun-Han Lin

The growing demand for low-cost, large-scale and flexible electronics has led to a boost in research on organic semiconductors (OSC). Understanding structure-packing-property relationships (SPPR) and the role of molecular building blocks in charge transport enables the development of effective rational design strategies, which helps in accelerating the search of promising of OSCs. Therefore, the original work presented in this thesis addresses these two aspects, with a focus on organic hole transport materials (HTM) utilized in perovskite solar cells. In the first part of this thesis, we place emphasis on revealing the SPPR of triphenylamine (TPA)-based HTMs utilizing multi-scale simulations involving molecular dynamics, density-functional theory and kinetic Monte-Carlo techniques. In the first example, we investigated the role of heteroatoms, presence of hexyl chains and substitution positions on charge transport for truxene derivatives. In particular, the impact of the presence of hexyl chain on hole mobility (ÃÅ) was identified, where hexyl-substituted truxene compounds possess hole mobilities an order of magnitude lower than those of their bare-core counterparts. The lower mobility originates primarily from the steric effect of hexyl chains, which prevents the truxene dimer from adopting a face-to-face arrangement. Due to the crucial role of the hexyl chain, we further investigated the effect of alkyl chain length on charge transport. As the alkyl chain is elongated, the reorganization energy (Î») remains unchanged, while the electronic coupling (V) and energetic disorder (ÃÂ) decrease simultaneously. Since V decreases much faster than ÃÂ does, ÃÅ gradually decreases with increasing alkyl chain length. Finally, we reveal the underlying mechanism of the multiarm effect on ÃÅ. By increasing the number of carbazole arms substituted on the TPA core, all transport parameters are decreased, which overall leads to an increase in ÃÅ. The second part focuses on the development of a fragment-based decomposition scheme for reorganization energy (FB-REDA) and electronic coupling (FB-ECDA). The total ÃÂ» of a molecule is partitioned into fragment reorganization energies utilizing local fragment vibrational modes. We demonstrate the usefulness of FB-REDA by successfully reduce the ÃÂ» of a dopant-free HTM (TPA1PM, ÃÂ» = 213 meV) by nearly 50% (TPD3PM, ÃÂ» = 108 meV) using rational design strategies based on the FB-REDA results. Similarly, the total V between two molecules in a dimer was decomposed into fragment-fragment electronic coupling terms using FB-ECDA. Combined with percolation and dimer composition analysis, we successfully established the relationship between molecular packing and electronic coupling for two series of molecules.

EPFL2020

FB-ECDA: Fragment-based Electronic Coupling Decomposition Analysis for Organic Amorphous Semiconductors

Kun-Han Lin

We present a fragment-based decomposition analysis tool (FB-ECDA) for the electronic coupling of charge transfer processes. This tool provides insight on the sophisticated relationship between molecular packing, electronic coupling, and the molecular transport network present in organic amorphous semiconductors. On the basis of atomic orbitals, FB-ECDA decomposes the total electronic coupling into individual electronic coupling terms arising from each molecular building blocks in a straightforward manner. The usefulness of this approach is demonstrated by revealing the structure-packing-property relationships for two series of molecules differing by the number of arm substituents and acene core length. Overall, we provide insight on the design of organic semiconductors exhibiting efficient charge transport network through achieving a subtle balance between molecular packing and electronic structure. We expect FB-ECDA to be a valuable tool for understanding sophisticated charge transfer processes in amorphous systems and guiding the rational design of organic semiconductors.

AMER CHEMICAL SOC2020

Rational Design of Hole Transport Materials: Tools and Structure-Packing-Property Relationships

Kun-Han Lin

EPFL2020