Porphyrin dimer as efficient optical thermometer: Experimental and computational evaluation of the barrier to torsional rotation

The photophysics of conjugated metal-linked oligomers of porphyrins has been investigated spectroscopically and by quantum chemical calculations. The influence of the conformation on the ground and first singlet excited states has been studied. The absorption spectra and quantum chemical calculations have revealed two different dimer conformations. The UV–vis spectra calculated by the TD-DFT method are quite comparable with the experimental spectra of the two species. The calculated value of the torsional energy barrier is ΔЕ = 3.4 kJ‧mol−1. Studies of the temperature dependence of the dimer fluorescence spectrum have shown the fundamental possibility of using it as a contactless luminescent temperature sensor. Information about the local temperature can be obtained from the calculated temperature dependence of FIR, which represents a monotonic pseudo-linear trend.