Comprehensive review of photophysical parameters (ε, Φf, τs) of tetraphenylporphyrin (H2TPP) and zinc tetraphenylporphyrin (ZnTPP) – Critical benchmark molecules in photochemistry and photosynthesis

Abstract Tetraphenylporphyrin (H2TPP) and zinc tetraphenylporphyrin (ZnTPP) are widely used benchmark molecules in diverse photochemical studies given facile synthetic access, rich visible-region spectra, and broad structural analogy to chlorophylls. Yet the literature values for each key photophysical parameter – the molar absorption coefficient (e), fluorescence quantum yield (Φf), and also singlet excited-state lifetime (τS) – vary over an astonishing range. Here, a comprehensive literature review (∼1940–present) encompassing 871 publications is reported for these essential parameters. Each parameter is determined by measurement with distinct instrumentation and suffers idiosyncratic sources of error. The best values for H2TPP are e = 460,000 cm―1·M―1, Φf = 0.090, and τS =12.8 ns in Ar-purged toluene (Φf = 0.070, τS =9.9 ns in toluene in air); the best values for ZnTPP are e = 560,000 cm―1·M―1, Φf = 0.030, and τS =2.1 ns in Ar-purged toluene (Φf = 0.029, τS =2.0 ns in toluene in air). The choice of values for such parameters has far-reaching consequences in photochemistry ranging from fluorescence (or Forster) resonance energy transfer (FRET) processes to assessments of molecular brightness.