On the flexibility of carboranylalkylthio substituents in porphyrazines and its relevance to the photophysical properties

Abstract

Ultrafast transient absorption spectrometry and DFT/TDDFT calculations reveal that following photoexcitation, carboranyl- and carboranyl-free alkylthioporphyrazines deactivate by the pathway S₁(π,π*)→S_n(C_β-2p_z/S_l.p.,π*)→ground state. The presence of quenching singlet excited states with predominantly C_β-2p_z/S_l.p.,π* character immediately below the primarily photogenerated S₁(π,π*) state is a consequence of the electronic structure changes induced by the inherent flexibility of the alkylthio chains.