Photophysical properties are the set of quantities that describe how a molecule or a material takes up light and disposes of the excitation energy, including absorption and emission spectra, fluorescence and phosphorescence quantum yields, excited-state lifetimes, and the rate constants of internal conversion, intersystem crossing and energy transfer. The quantum yield is the ratio of emitted to absorbed photons; it is usually measured against a standard or, for scattering and weakly emitting samples, in an integrating sphere, where reabsorption has to be corrected [1]. The luminescence of the sphere wall itself also biases the result unless it is subtracted [2]. Typical fluorescence lifetimes fall in the nanosecond range, and a yield below unity means that non-radiative channels compete with emission; which channel dominates depends on the gap between the excited states, the spin-orbit coupling and the rigidity of the environment [3]. Intersystem crossing into the triplet manifold can be quantified by quantum-chemical calculation of the spin-orbit matrix elements and competes with fluorescence on the picosecond-to-nanosecond scale [4]. Time-resolved methods, femtosecond transient absorption among them, follow the excited population directly and resolve the individual decay channels [5]. Reported values for one compound still scatter between laboratories, mostly because of reabsorption, oxygen quenching and the choice of standard [2].
- fluorescence quantum yield
- excited state
- intersystem crossing
- fluorescence lifetime
- transient absorption
- photoluminescence
References
- Gaigalas, A.K.; Wang, L.; Measurement of the fluorescence quantum yield using a spectrometer with an integrating sphere detector. Journal of Research of the National Institute of Standards and Technology 2008, 113, 17, 10.6028/jres.113.004.
- Valenta, J.; Photoluminescence of the integrating sphere walls, its influence on the absolute quantum yield measurements and correction methods. AIP Advances 2018, 8, 105123, 10.1063/1.5052601.
- Heldt, J.R.; Heldt, J.; Ston, M.; Diehl, H.A.; Photophysical properties of 4-alkyl- and 7-alkoxycoumarin derivatives. Absorption and emission spectra, fluorescence quantum yield and decay time. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 1995, 51, 1549-1563, 10.1016/0584-8539(95)01467-9.
- Daza, M.C.; Doerr, M.; Salzmann, S.; Marian, C.M.; Thiel, W.; Photophysics of phenalenone: quantum-mechanical investigation of singlet-triplet intersystem crossing. Physical Chemistry Chemical Physics 2009, 11, 1688, 10.1039/b815724c.
- Zhang, Y.; Beckstead, A.; Hu, Y.; Piao, X.; Bong, D.; Kohler, B.; Excited-State Dynamics of Melamine and Its Lysine Derivative Investigated by Femtosecond Transient Absorption Spectroscopy. Molecules 2016, 21, 1645, 10.3390/molecules21121645.