INFORMATION ENTROPY OF CHEMICAL REACTIONS: A NOVEL METHODOLOGY FOR DIGITAL ORGANIC CHEMISTRY

The development of the computational methodology of structural descriptors, which are the basic concept of mathematical and digital chemistry, involves expanding the field of their application. In particular, the development of methods for calculating descriptors relating to the structure of the ensembles of particles is an urgent task. Information entropy is widely used to describe the chemical structures of molecules but its application to molecular assembles and chemical reactions is limited. We have proposed a new approach to calculating the information entropy of a molecular ensemble: besides the contributions of individual molecules, it takes into account the corporative entropy arising when molecules form an ensemble. This approach provides a fresh view on calculating the change in information entropy in chemical reactions approximated as the transformation of one ensemble (reactants) into another (molecular ensemble of products). The new method of calculation allows separate assessing the contributions to a chemical reaction associated with a change in the molecular structure and molecule size.

Study of a carbazole-bromobenzothiadiazole derived fluorescent molecular rotor: crystal structure, redox activity, and solvatofluorochromic effects

This work investigated the properties of a four-component molecular ensemble, in which a carbazole (CBz) donor and a benzothiadiazole (BTD) acceptor are connected through a phenylthiophene (PT) bridge. The multiple...

Multiphoton Excitation of Organic Molecules in a Cavity – Superradiance as a Measure of Coherence

<div>Coherent excitation of a molecular ensemble coupled to a common radiation mode can lead to the collective emission of radiation known as superradiance. This collective emission only occurs if there is an entanglement between the molecules in their ground and excited state and can therefore serve as a macroscopic measure of coherence in the ensemble. Reported here are wave packet propagations for various pyrazine models of increasing complexity and molecular ensembles thereof. We show that ensemble coherence upon photoexcitation can prevail up to relatively long time scales, although the effect can diminish quickly with increasing ensemble size. Coherence can also build up over time and even reemerge after the molecules have passed through a conical intersection. The effect of the pump-pulse characteristics on the collective response of the molecular ensemble is also studied. A broad-band pulse imprints a large amount of initial coherence to the system, as compared to a longer pulse with a smaller spread in the frequency domain. However, the differential effects arising from a different pulse duration and coherent bandwidth become less prominent if the emission of light from the ensemble takes place after a non-adiabatic decay process.</div>

Multiphoton Excitation of Organic Molecules in a Cavity – Superradiance as a Measure of Coherence

<div>Coherent excitation of a molecular ensemble coupled to a common radiation mode can lead to the collective emission of radiation known as superradiance. This collective emission only occurs if there is an entanglement between the molecules in their ground and excited state and can therefore serve as a macroscopic measure of coherence in the ensemble. Reported here are wave packet propagations for various pyrazine models of increasing complexity and molecular ensembles thereof. We show that ensemble coherence upon photoexcitation can prevail up to relatively long time scales, although the effect can diminish quickly with increasing ensemble size. Coherence can also build up over time and even reemerge after the molecules have passed through a conical intersection. The effect of the pump-pulse characteristics on the collective response of the molecular ensemble is also studied. A broad-band pulse imprints a large amount of initial coherence to the system, as compared to a longer pulse with a smaller spread in the frequency domain. However, the differential effects arising from a different pulse duration and coherent bandwidth become less prominent if the emission of light from the ensemble takes place after a non-adiabatic decay process.</div>

Graphene transistors for real-time monitoring molecular self-assembly dynamics

Mastering the dynamics of molecular assembly on surfaces enables the engineering of predictable structural motifs to bestow programmable properties upon target substrates. Yet, monitoring self-assembly in real time on technologically relevant interfaces between a substrate and a solution is challenging, due to experimental complexity of disentangling interfacial from bulk phenomena. Here, we show that graphene devices can be used as highly sensitive detectors to read out the dynamics of molecular self-assembly at the solid/liquid interface in-situ. Irradiation of a photochromic molecule is used to trigger the formation of a metastable self-assembled adlayer on graphene and the dynamics of this process are monitored by tracking the current in the device over time. In perspective, the electrical readout in graphene devices is a diagnostic and highly sensitive means to resolve molecular ensemble dynamics occurring down to the nanosecond time scale, thereby providing a practical and powerful tool to investigate molecular self-organization in 2D.