The Number-Average Lifetime of Nonexponential Fluorescence Decays Is a Most Reliable Parameter

This study challenges the 40 year-old consensus that no quantitative information can be retrieved by fitting a nonexponential fluorescence decay (NEFD) with a sum of exponentials (SoE) due to the well-accepted understanding that such analyses are unreliable. This challenge is mounted by demonstrating that as long as simple precautions are adhered to, the number-average lifetime (⟨τ⟩) and the molar fraction (fNQ) of dyes that are not undergoing a photophysical process are most reliable parameters, despite being calculated from the unreliable pre-exponential factors and decay times retrieved from the SoE analysis of NEFD. Consequently, this study validates and justifies the use of ⟨τ⟩ and fNQ for the characterization of the many photophysical processes resulting in NEFD.