Since DHP is a negative T-type photochrome the reversal was also expected in thermal conditions. The stability and the reversibility of the system at room temperature was studied. The thermal reversal (1o→1c) of the system was achieved with the regeneration of the colour when the solution of 1o (10M in CHCl3:CH3CN 1:1, purged with N2) was thermally heated at 70 o C (Figure ). The thermal 1o→1c reaction followed a first-order kinetics (k = 9.2 × 10 -2 min -1 ) (Figure ). Detailed analysis of the various thermodynamic parameters for the kinetics of thermal reversal was obtained from variable temperature spectroscopic studies which have been discussed in the supporting information (table ).