Multiwavelength Control of Mixtures Using Visible Light Absorbing Photocages
Selective deprotection of functional groups using different wavelengths of light is attractive for materials synthesis as well as for achieving independent photocontrol over substrates in biological systems. However, wavelength-selective activation is difficult to achieve with common UV-absorbing photoremovable protecting groups (PRPGs) because it is difficult to separate the chromophore absorption profiles. Moreover, deep UV irradiation of photocages can result in cellular phototoxicity. Here, we investigated the ability of recently-developed visible light absorbing BODIPY-derived PRPGs and a coumarin-derived PRPG to undergo wavelength selective activation in order to identify well-behaved pairs of PRPGs that allow independent optical control over a mixture of photocaged substrates using more biologically benign long-wavelength light. The three pairs of PRPGs tested have complete selectivities for cleaving the longerwavelength absorbing photocage first, and fair to excellent selectivities for releasing the lower-wavelength absorbing PRPG first when mixtures were irradiated in solution. When the PRPGs are attached to the same substrate, irradiating the shorter-wavelength absorbing PRPG results in energy transfer, but the PRPGs can be cleaved in a sequential manner starting by deprotecting the longest wavelength absorbing photocage first and then removing the lower-wavelength absorbing PRPG. A mixture of the three photocages could be sequentially reacted using common red, green, and far-UV (365 nm) LED irradiation.