The photochromism of 1 can also be followed using IR spectroscopy. Magnetic studies DC magnetic properties of 1 and 2 before and after irradiation DC (direct current) magnetic measurements for 1, 1UV and 1vis as well as for 2 and 2UV were performed using a SQUID magnetometer. For 1, 1UV and 1vis, the temperature dependence was recorded in the 2-140 K range (limited due to the freezing point of pentane) and the external DC field of 0.1 T (Figure ) while for 2 and 2UV a typical 2-300 K range could be used (Figure ). The magnetic field dependence at a constant temperature of 1.8 K was recorded in the 0 -7 T range for both systems (insets in Figures and).