The development of methods for the generation of site-selective interstrand crosslinks (ICLs) in synthetic oligonucleotides provides a platform for the study of ICL repair mechanisms and the stabilisation of DNA-based materials. Our group has previously reported on the use of a furan moiety as a masked reactive functionality for ICL generation and recently introduced the use of O as an efficient light-induced oxidant. Here, the use of porphyrin-based photosensitizers (PSs) has been explored for ICL generation. The efficiency of the ICL reaction has been investigated using PSs added into solution as well as attached to oligonucleotide probes. Interestingly, even a highly hydrophobic phthalocyanine was able to produce ICLs. Either in solution or conjugated to an ON, chlorin e6 was the most efficient ICL generator for the current purpose.

Singlet oxygen-induced DNA interstrand crosslinking was achieved at intracellularly relevant concentrations using a templated reaction setup. The target oligonucleotide serves as a template ensuring proximity between a "furan warhead"-containing probe and an activator probe containing a photosensitizer able to generate 1 O2. Visible light irradiation of this self-activating assembly allows to achieve highly selective interstrand crosslinking at concentration levels relevant for intracellular applications.