Synthesis, fluorescence properties and applications of two novel oxadiazole-based stilbene optical brighteners as UV protectants for insect baculovirus

• Two novel symmetrical stilbene optical brighteners were efficiently synthesized.
• The sodium sulfonate unit was successfully introduced into the molecular structure.
• The brighteners exhibited bright blue emission with high fluorescence quantum yields.
• Compound 3b displayed more obvious UV-protection and enhancement in SINPV system.

Two novel symmetrical stilbene optical brighteners based on 1,3,4-oxadiazole bearing sodium sulfonate unit were synthesized. The two target compounds were characterized by NMR and elemental analysis. The photophysical processes of the target compounds were investigated by UV–Vis absorption and fluorescence emission spectra in different solutions. The two optical brighteners were tested as radiation protectants for the Spodoptera litura nuclear polyhedrosis virus (SINPV) against 2nd-instar S. litura larvae. The results indicate that the two compounds exhibit strong blue fluorescence emission, and the fluorescence quantum yield in DMF is 0.86 and 0.75, respectively. The insecticidal effect of SINPV is increased by the addition of the two compounds and especially the compound 3b shows more obvious synergy effect.