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 ν6a 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 Eb<1552 cm−1.