Cyanine dyes, which are important class of probes used extensively as antibody and other biomolecule labels, have been found to undergo photoconversion reaction resulting to the formation of species with different absorbance/emission wavelengths. A novel reaction involving the direct conversion of the simplest heptamethine cyanine to trimethine cyanine via the loss of a 4-carbon molecule along the polymethine chain is reported. A density functional (DFT)-supported model is proposed to describe this singlet oxygen (1O2)-mediated phototruncation reaction. The singlet oxygenation of heptamethine cyanine leads to an allene hydroperoxide intermediate which undergoes a retro-Diels-Alder process resulting to a subsequent 4-carbon loss to trimethine cyanine. The direct conversion process is supported experimentally with fluorescence and mass spectrometry results. This 4-carbon truncation reaction adds to growing body of cyanine reactivity and may provide an optical tool leading to a substantial blue-shift of ∼200 nm. We thank the National Science Foundation (CHE-2154133) and the Intramural Research Program of the National Institutes of Health, National Cancer Institute (NCI), Center for Cancer Research for funding. We also thank the San Diego Super Computer (SDSC) Expanse for the allocation provided to perform the DFT study.
No takes yet. Share an insight, caveat, or question.
Lapoot et al. (2024) studied this question.