Communication: Trapping upconverted energy in neat platinum porphyrin films via an unexpected fusion mechanism.

ABSTRACT

Direct observation of an unexpected product from excited state fusion of two excited triplet states in platinum octaethylporphyrin is reported. Transient spectroscopy was used to identify the product as a metal centered (d, d) state that decays slowly compared with the rate of fusion. The reaction was demonstrated to be second order with a rate coefficient of k(TTF) = (5.4 ± 0.4) × 10(-10) cm(3) · s(-1). The results contrast with the common assumption that fusion proceeds directly to annihilation via rapid non-radiative deactivation of the products. Following visible photo-excitation, the fusion process results in energetic upconversion of the incident photons stored in the higher energy (d, d) state at irradiances below the threshold for multi-photon absorption.