The photophysics and photochemistry of weakly bound dimers of s-tetrazine

Abstract

Energy redistribution within the excited states of the planar and T‐shaped dimers of s‐tetrazine was monitored by dispersed emission following selective vibronic excitation. When the dimer contained excess vibrational energy above the electronic origin, three processes were observed: (1) energy transfer from the initially populated ν_6a vibration (in‐plane stretch) to low frequency dimer vibrations involving motion of one monomer subunit with respect to the other; (2) electronic energy transfer from the high energy ring (∥ polarized) to the low energy ring (⊥ polarized) in the T‐shaped dimer; and (3) photodissociation of the T‐shaped dimer into monomer subunits. Simultaneously observed fluorescence from the initially populated state allows us to estimate the rates at which these processes occur. The observation of photodissociation (τ=38 ps) of the T‐shaped dimer with an input of 1595 cm⁻¹ of excess vibrational energy yields an estimate for the binding energy in the ground state E_b−¹.