High-throughput Virtual Screening of Existing Organic Chromophores for Materials Discovery

High-throughput virtual screening (HTVS) has, in recent years, become an extremely powerful tool in the discovery of novel organic optoelectronics due to advances in hardware and architecture, facile access to both experimental and high-level theoretical datasets and vast improvements to quantum chemical methods. We have already taken advantage of HTVS¹ by considering the Cambridge Structural Database,² where we have successfully predicted candidates for singlet fission,^3,4 thermally activated delayed fluorescence,⁵ non-fullerene electron acceptors⁶ and luminescent crystals which show superradiance or near-infrared emission.⁷ The main advantage of searching a database with known experimental structures, along with low bias, is the potential to source candidates and test them experimentally with no worry regarding synthetic feasibility; a serious downfall of any <i>de novo</i> study.<br/><br/>Our latest HTVS study considers the much larger ZINC database;⁸ a set of many millions of small-to-moderate organic compounds. With a quote of approximately 13 million structures that are ‘commercially available’ this unfeasibly large set forms the library of our study. With innovation in the form of conjugated core clustering, conformational analysis, accurate experimental calibration and rigorous protocol benchmarking, we are able to accurately assess, with TD-DFT, the electronic structures for the entire set of 13 million with the computation of approximately 150 thousand unique structures. This forms one of the largest quantum chemical datasets to date.<br/><br/>The ZINC database of commercially available compounds was chosen specifically for easy access to real compounds which can be ordered and tested in our own in-house laboratories. From of our wealthy database, we have verified our protocol experimentally and identified promising materials for both near-infrared and anti-Kasha dual emission by testing over thirty unique compounds using absorption and fluorescence-lifetime spectroscopy. These properties are extremely rare and coveted and have applications in a wide range of photonic devices.<br/><br/>An additional, extremely rare phenomenon that has been sought recently within our optoelectronic database is the violation of Hund’s rule in some molecules, or in other words, compounds that exhibit an inverted singlet-triplet gap⁹ due to atom-localised intramolecular charge transfer (<i>i.e.</i> lowering the exchange energy to degeneracy between S₁ and T₁ state) coupled with spin polarisation in the S₁ state due to large contributions from double excitations. This becomes invaluable for devices (e.g. OLEDs) which seek to harvest triplet excitons by making the reverse intersystem crossing energetically favourable. Promising theoretical results using high-level multireference wavefunction methods suggest totally new design rules beyond the known heptazine case due to the low bias in our datasets.<br/><br/><br/><b>References</b><br/><br/>1. Ö. H. Omar, T. Nematiaram, A. Troisi and D. Padula, <i>Sci. Data</i>, 2022, <b>9</b>, 54.<br/>2. C. R. Groom, I. J. Bruno, M. P. Lightfoot and S. C. Ward, <i>Acta Crystallogr. Sect. B Struct. Sci. Cryst. Eng. Mater.</i>, 2016, <b>72</b>, 171–179.<br/>3. D. Padula, Ö. H. Omar, T. Nematiaram and A. Troisi, <i>Energy Environ. Sci.</i>, 2019, <b>12</b>, 2412–2416.<br/>4. Ö. H. Omar, D. Padula and A. Troisi, <i>ChemPhotoChem</i>, 2020, <b>4</b>, 5223–5229.<br/>5. K. Zhao, Ö. H. Omar, T. Nematiaram, D. Padula and A. Troisi, <i>J. Mater. Chem. C</i>, 2021, <b>9</b>, 3324–3333.<br/>6. Z. W. Zhao, Ö. H. Omar, D. Padula, Y. Geng and A. Troisi, <i>J. Phys. Chem. Lett.</i>, 2021, <b>12</b>, 5009–5015.<br/>7. T. Nematiaram, D. Padula and A. Troisi, <i>Chem. Mater.</i>, 2021, <b>33</b>, 3368–3378.<br/>8. J. J. Irwin and B. K. Shoichet, <i>J. Chem. Inf. Model.</i>, 2005, <b>45</b>, 177–182.<br/>9. P. De Silva, <i>J. Phys. Chem. Lett.</i>, 2019, <b>10</b>, 5674–5679.