Method of determination of emission properties of very weakly emitting species ensuring elimination of emission of impurities

Spectral and photophysical properties of cytisine in acetonitrile - Theory and experiment

Spectral and photophysical properties of (-)-cytisine that is used as a smoking cessation aid, and which derivatives are promising tools in a treatment of neurological diseases, were investigated in acetonitrile, non-specifically interacting solvent with a polarity similar to water. The two chair conformers of cytisine were found the most stable in the ground state S₀ and the lowest excited singlet state S₁(π,π*), wherein axial one was characterized by a significantly larger abundance, fluorescence lifetime 0.15 ns and fluorescence quantum yield 0.008. The S₁(π,π*) excited state of both cytisine conformers deactivated almost exclusively via internal conversion.

Spectral and Photophysical Behavior of Cytisine in n-Hexane. Experimental Evidence for the S1(n,π*) → S0 Fluorescence

Spectral and photophysical properties of (-)-cytisine (the compound used as a smoking cessation aid and a potential drug in Alzheimer's and Parkinson's diseases) were investigated. The two conformers of cytisine, whose presence in the S₀ state has been earlier proved by the NMR and IR methods as well as in theoretical calculation, in nonpolar n-hexane show a rarely observed prompt fluorescence from the S₁(n,π*) excited state. This observation is unambiguously evidenced by very small radiative rate constants of these two emitting conformers, k_F = 7.4 × 10⁵ and 3.0 × 10⁵ s^-1. Their lifetimes in the S₁(n,π*) state are relatively long, τ_S1 = 1.9 and 6.7 ns; therefore, their fluorescence quantum yield is relatively high ϕ_F ∼ 10^-3. The long-wavelength band in the cytisine absorption originates from the excitation to the S₂(π,π*) state, while the S₁(n,π*) state is not observed in this spectrum. Thus, the excited state S₂(π,π*) is manifested only in the absorption spectrum, while the excited state S₁(n,π*) is seen only in the fluorescence spectrum, so cytisine in n-hexane is characterized by close lying (n,π*) and (π,π*) excited singlet states.

The application of a UHPLC system to study the formation of various chemical species by compounds undergoing efficient self-aggregation and to determine the homodimerization constants (KDM) with values in the high range of 106–1010 M−1

This work demonstrates a new concept for the use of UHPLC method for identification of the species formed by a self-aggregating compound depending on its concentration and solvent used and to determine homodimerization constants, K_DM = 10⁶–10¹⁰ M⁻¹.

Hydrogen-bonded 4H-1-benzopyrane-4-thione–water complexes properties in the S2 excited state: the mechanism and dynamics of deactivation

Unexpected results of spectral emission and photophysical study of S₂-excited 4H-1-benzopyrane-4-thione (BPT) in water solution were explained by intermolecular hydrogen bonding.

Standards for photoluminescence quantum yield measurements in solution (IUPAC Technical Report)

The use of standards for the measurement of photoluminescence quantum yields (QYs) in dilute solutions is reviewed. Only three standards can be considered well established. Another group of six standards has been investigated by several independent researchers. A large group of standards is frequently used in recent literature, but the validity of these is less certain. The needs for future development comprise: (i) confirmation of the validity of the QY values of many commonly used standard materials, preferably in the form of SI traceable standards; (ii) extension of the set of standard materials to the UV and near-IR spectral ranges; and (iii) good standards or robust protocols for the measurements of low QYs.