We identified molecular fragments that determine high maximum oscillator strength. To discover bigger and more diverse molecular fragments, we extracted information from the RF results using ECFP6 with 16384 bits. To confirm that the oscillator strength distribu- tions of the identified fragments are statistically higher than the average, the p-value of the distribution was calculated by the Wilcoxon rank sum test. The fragments satisfying the following conditions were selected for further analysis; 1) the p-value is lower than 0.0001, 2) the mean oscillator strength of molecules containing the fragment is over 0.3, and 3) the number of molecules containing the fragment is over 10. The eight fragments satisfying the above criteria were retrieved from the PubchemQC database. These fragments are presented in the ascending order of p-value, descending order of statistical significance (Figure ). Overall, it is identified that nitrogen-containing heterocycles are playing important roles in inducing high oscillator strength of a molecule. The first six statistically significant fragments have one or more nitrogen atoms inside a ring structure. The most statistically significant fragment contains an indazole-like structure, the fragment c(cc)(c(c)c)n(C)n (Figure ). The 69 molecules containing the indazole-like structure have the lowest pvalue of 1.158*10 -28 and the second highest mean oscillator strength, 0.415 (Figure ).