Molecules which display two optical emission bands are very rare as they violate Kasha’s rule, which states that fluorescence is normally observed only from the lowest energy excited state (S1) due to efficient internal conversion from higher states after excitation. Here, we develop a combined virtual and experimental screening workflow to find new anti-Kasha emitters among those with a large energy gap between S1 and S2; a condition that favours optical emission from the higher excited state because of a reduced internal conversion rate. 140,000 chemically diverse and commercially available molecules are filtered through a computational funnel based on their computed S1-S2 gap, transition intensities and structural rigidity before being ranked by cost and purity from up-to-date information from the chemical supply chain. The absorption and fluorescence spectra of a number of candidates has been measured for 19 potential candidates. Seven of them display anti-Kasha emission (five displaying single emission from S2 and two displaying dual emission). The approach exemplifies the great potential of virtual screening approaches that take into account chemical availability and lead to an immediate validation of the predictions.
Omar et al. (Wed,) studied this question.