Chemosensors with perylenediimide and naphthalenediimide based on photoinduced electron transfer

Abstract

Novel pH sensing compounds based on perlyenediimide and naphthalenediimide fluorophores were designed and synthesized from commercially available di-brominated reagents. Imidization with N,N-dimethylethylenediamine was carried out symmetrically on both fluorophores, and symmetric bay-substitution of the perylenediimide was carried out for the bromide atoms with 5 to 7-membered aliphatic rings of pyrrolidine, morpholine and azepane. Bay-substitution of the naphthalenediimide was accomplished with pyrrolidine. Four novel H+- driven YES logic gates of the model format “Receptor-Spacer1-Fluorophore-Spacer2-Rceceptor” were synthesized. The molecules are modulated by photoinduced electron transfer (PET) and internal charge transfer (ICT) mechanisms, and switched on in the presence of acid. The four compounds and the dibrominated intermediates were studied via UV-visible absorption and fluorescence emission spectroscopy. Through these techniques, the photophysical and logic characteristics of the compounds were investigated in different solvents, namely water, methanol, THF and chloroform. Solvachromaticity was seen in almost all cases, as evidenced by vibrant colour changes and fluorescence enhancements were seen to varying degrees in the different solvents on addition of acid. Notably, the newly synthesized compounds emit in the near infra-red (NIR) region, which could open up an array of future biological applications.