Figure 2.

Mechanistic studies of cyanine phototruncation. (a) Products observed following irradiation of 2-d₃ or an equimolar ratio of 2 and 2-d₆ in PBS (100 μM, 1 mL, with 0.01% DMSO, pH = 7.4) with 630 nm LED at 0.2 W cm^–2 for 60 min and monitored by HRESIMS. (b) Evaluating the scope of cyanine phototruncation in PBS (100 μM, 1 mL, with 0.01% DMSO, pH = 7.4) upon irradiation of a heptamethine probe (1) with 740 nm LED (at 0.5 mW cm^–2, 30 min) and pentamethine probes (2 and 6) with 630 nm LED (at 0.2 mW cm^–2, 60 min). (c) Evaluating the truncation of 2 to 3 with independently generated ROS (see Methods for detailed experimental procedures). (d) Effect of pH on conversion of 2 (50 μM) to 3 in Britton–Robinson buffer (0.04 M boric acid, 0.04 M phosphoric acid, and 0.04 M acetic acid that has been titrated to the desired pH with 1 M sodium hydroxide) upon irradiation with 630 nm LED at 0.2 W cm^–2 for 60 min and monitored by UV–vis. Yields were calculated based on the absorption coefficients (ε) of 2 (230 400 M^–1 cm^–1) and 3 (150 000 M^–1 cm^–1) in water. Experiments were conducted in triplicate with the error expressed as the standard deviation of the mean.