fromage : A library for the study of molecular crystal excited states at the aggregate scale

2021

J. Mater. Chem. C

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Section: Methodsmentioning

confidence: 99%

Excited state mechanisms in crystalline carbazole: the role of aggregation and isomeric defects

Hernández

2021

J. Mater. Chem. C

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“…To simulate the excited states in the molecular crystal, we created cluster models of Cz and applied the QM-QM' ONIOM schemes implemented in fromage [23,24].…”

Section: Methodsmentioning

confidence: 99%

Excited State Mechanisms in Crystalline Carbazole: The Role of Aggregation and Isomeric Defects

Hernández¹,

2021

Preprint

The molecule of Carbazole (Cz) is commonly used as a building block in organic materials for optoelectronic applications, acting as light-absorbing, electron donor and emitting moiety. Crystals from Cz and derivatives display ultralong phosphorescence at room temperature. However, different groups have reported inconsistent quantum efficiencies for the same compounds. In a recent experimental study by Liu et al. (Nature Materials 2021, 20, 175-180), the ultralong phosphoresce properties of Cz have been associated with the presence of small fractions of isomeric impurities from commercially available Cz. In this paper, we use state-of-the-art computational approaches to investigate light-induced processes in crystalline and doped Cz. We revisit the role of aggregation and isomeric impurities on the excited state pathways and analyse the mechanisms for exciton, Dexter energy transfer and electron transport based on Marcus and Marcus-Levich-Jortner theories. Our excited state mechanisms provide a plausible interpretation for the experimental results and support the formation of charge-separated states at the defect/Cz molecular interface. These results contribute to a better understanding of the factors enhancing the excited state lifetimes in organic materials and the role of doping with organic molecules.

“…The principal axis was defined as the vector tracing the longest interatomic distance and the secondary axis its perpendicular vector on the averaged plane. 7 This process is represented for a dimer of the 3P crystal in Figure 2. All molecules have rotational symmetry about both of the axes when defined this way apart from HBT which has an inherent orientation.…”

Section: Computational Detailsmentioning

confidence: 99%

The role of conical intersections on the efficiency of fluorescent organic molecular crystals

Rivera¹,

Stojanović²,

2020

Preprint

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Organic molecular crystals are attractive materials for luminescent applications due to their promised tunability. However, the link between chemical structure and emissive behaviour is poorly understood due to the numerous interconnected factors which are at play in determining radiative and non-radiative behaviours at the solid state level. In this study, we investigate thirteen luminescent molecular crystals and apply newly implemented tools to study their geometric properties and constituent dimer excitonic coupling values. We then focus on the excited state decay pathways of five of the molecules. The competition between radiative and nonradiative processes was used to rationalise the different fluorescence quantum yields across systems. We found that due to the prevalence of sheet and herringbone packing in organic molecular crystals, the conformational diversity of crystal dimers is limited. Additionally, similarly spaced dimers have exciton coupling values of similar order within a 50 meV interval. Finally, we found that the accessibility of conical intersection geometries was a robust indicator of the role of nonradiative decay in the excited state mechanism of most molecules. The conical intersections all displayed a measure of rotation and puckering, where purely rotational conical intersections in vacuum lead to high energy puckered conical intersections in the crystal phase.