The samples
were irradiated at 293 K directly in the EPR resonator (High
Sensitivity Probe-head, Bruker), and the EPR spectra were recorded
in situ. The irradiation source was a UV LED monochromatic radiator
(lmax ¼ 365 nm or lmax ¼ 400 nm; Bluepoint LED, H€onle UV
Technology). The value of the irradiance (lmax ¼ 365 nm;
14 mW cm2) within the EPR cavity was determined using a UVX radiometer (UVP, USA).