Triplet quantum yield determination with noncollinear double pulse fluorescence applied to a new class of cationic free-based porphyrins

Abstract

Accurate and simple determination of key photophysical parameters, such as triplet quantum yield and intersystem crossing rate, holds significant technological importance for a series of modern biological, optical, and photonics applications. Techniques such as double- or multi-pulse fluorescence (DPF or MPF) have flexible requirements on the photophysical parameters of the samples and allow for the measurement on nanosecond timescales of the triplet quantum yield. Here, we present a novel noncollinear DPF configuration that facilitates the implementation of DPF setups for ultrafast pulsed laser systems with different divergences, beam profiles and wavelengths. We develop a framework for performing DPF experiments in both collinear and noncollinear geometries using two models, which consider either a flat-top or a Gaussian beam profile and calibration samples. In both models, a novel correction procedure for imperfect spatial overlap is implemented, which is a necessity for noncollinear DPF and most of the collinear DPF setups available. We demonstrate that the noncollinear configuration produces results equivalent within 5% relative difference to the traditional collinear setups when the flat-top beam profile model is used. Furthermore, treating the beam profile as Gaussian allowed triplet quantum yield determination at 50% lower laser fluence values due to the closer proximity to the experimental conditions. The new setup was demonstrated on a new class of recently synthesized cationic porphyrins, for which no previous photophysical characterization has been made. The triplet quantum yields of the porphyrins range between (25 ± 2)% and (35 ± 3)% and the accuracy of the technique is sufficient for the application to compounds with significant (>10%) triplet quantum yields.