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[Display omitted] • Two coumarin-based compounds with blue and green emission were prepared. • These compounds have the potential to be used as novel dual-state emitting luminogens. • Positive solvatochromism is found in these molecules. • These molecules exhibit Aggregation-Caused Red Shifted Emission. • Rewritable data storage has been demonstrated using the DSEgen molecule. The development of dual-state organic luminogens with high emission efficiency both in solution and solid phase is still a difficult task. Dual-state emissive fluorescent materials have proven to have a much broader application in several fields. Molecular design plays a significant role in fabricating switchable as well as tunable emissions. Nonetheless, the mechanism of dual-state emission needs to be studied further. Herein, two compounds, Blue-Yellow emissive material (BYEM) and Green-Red emissive material (GREM), have been designed and synthesized for a novel class of luminogens with dual-state emission (DSEgens) properties. These compounds emit luminously in solution state as well as solid state, with Aggregation Caused Red-Shifted Emission (ACRE) emission. Close-packed molecular structure and the steric hindrance effect can reduce the intramolecular rotation solution state, which accelerates the radiative transition of the compound in the solution state. On the contrary, in the solid state, the twisted structure and intermolecular C–H⋯π interactions can indorse the J -aggregation, which leads to the high fluorescence at the solid state. Significant red shift emission at solid state has been supported by theoretical calculations. On the other hand, by combining a partly shared donor–acceptor unit based on the twisted molecule, these compounds have shown good solvatochromic behavior. Gradual redshift emission has been observed as the solvent polarity is increased. These dual state highly emissive compounds can be applied in several industrial applications as well as the biomedical field. [ABSTRACT FROM AUTHOR]

[Display omitted] • Red emissive complexes with [Eu(TFFB) 3 L] stoichiometry were synthesized and investigated by spectroscopic studies. • Red emissive behavior of the complexes was characterized by photoluminescence study. • Photophysical characteristics of the mononuclear Eu(III) complexes were analyzed theoretically (JOES) and experimentally. • Probability amplitude distribution and the energy of HOMO and LUMO were estimated through DFT. Heteroleptic trivalent complexes of europium were prepared on reaction of EuCl 3 ·6H 2 O, fluorinated 1,3-diketone and 2,2′-bipyridine or its derivatives in the molar ratio of 1:3:1 respectively. Structural analysis of prepared complexes was done via spectral study. Luminescence features of synthesized complexes have been explored by the photoluminescence and decay spectral profile. Strong emission in the red spectral region was observed for Eu3+ ion corresponding to the electric dipole 5D 0 → 7F 2 hypersensitive transition. The radiative transition probabilities as well as the Judd-Ofelt parameters were computed and discussed. Complexes emit red light in the visible spectrum as illustrated by their CIE color coordinates are essential for creating effective display and lighting devices. [ABSTRACT FROM AUTHOR]

Abstract: The heteroatom effect on the radiative and reactive relaxations of E,E-1,2-distyrylbenzene (DSB) has been studied by stationary and time-resolved techniques on three compounds where the side phenyl (Ph) groups were replaced by 4′-pyridyl (4P), 2′-thienyl (2T) and 2′-furyl (2F) groups. Contrary to the case of the hydrocarbon, whose photoisomerization is accompanied by substantial degradation, the E,E → Z,E photoisomerization prevails in the hetero-analogues, particularly in the thienyl derivative. The lack of conjugation in these 1,2-substituted benzenes leads to a decrease in the fluorescence yield with respect to their 1,4 and 1,3 analogues (particularly in the presence of the heteroatoms), which is accompanied by an increase of the photoreaction quantum yield for the pyridyl- (significant) and thienyl- (very small) derivatives, whilst internal conversion is the prevalent deactivation pathway of the furyl derivative. [Copyright &y& Elsevier]

Abstract: The fluorescence behaviour of some new dyes based on the pyrazolo[3,4-b]quinoline (PQ) ring has been investigated. It was found that introduction of electron withdrawing and electron donating groups into pyrazolo[3,4-b]quinoline molecule causes an increase of the ground and excited state dipole moments but more important is introduction of the N,N-dimethylamine group directly into the pyrazolo[3,4-b]quinoline skeleton. Further introduction of the cyano groups in the peripheral phenyl rings brings about only minor changes in the transition dipole moments (absorption and fluorescence). Such compounds exhibit a CT fluorescence. The fluorescence of these compounds was investigated in terms of the radiative charge transfer transition to obtain the charge transfer parameters such as the energy gap between the charge transfer and the ground states, solvent reorganization energies and internal reorganization energy. The magnitude of these parameters was discussed in terms of a modern electron transfer theory and the parameters were used to calculate the rate constants for non-radiative CT transition. [Copyright &y& Elsevier]

• The temperature dependence of Trp fluorescence lifetime in solutions was studied. • A model was suggested of Trp molecules transition from the excited state to the CTS. • Reversal transition from the CTS to the excited state of Trp is considered. • Formation of the quasi-conductive band in the system of hydrogen bonds is considered. The temperature dependence of tryptophan fluorescence lifetime in an aqueous solution, aqueous solutions of glycerol (50 and 75 %, v/v) and dimethyl sulfoxide (DMSO) (50 and 75 %), and 1 M aqueous trehalose solution was studied in the range of –170 to +20 °C. In this temperature range, the fluorescence kinetics in all samples is best approximated by three exponential terms with characteristic times τ 1 ∼ 3 ns, τ 2 ∼ 4 ns, and τ 3 ∼ 15 ns at room temperature. Temperature dependences of fluorescence lifetimes for the fastest and medium components exhibited antisymbatic (antiphase) behavior in the temperature range of –60 to 10 °C. To explain this behavior, a model was suggested that takes into account the tryptophan (Trp) molecule transition from the excited state to the state with separated charges – charge transfer state (CTS), the transitions back to the excited state, and the radiative transitions of the CTS to the ground state. Mathematically, this model is equivalent to the model that we have suggested earlier in [Gorokhov et al. (2018) Biochemistry (Moscow) , 82 , 1615–1623] to describe the transitions between different rotamer forms of tryptophan. The obtained results can be used for interpreting the experimental temperature curves of tryptophan fluorescence lifetime in proteins. [ABSTRACT FROM AUTHOR]