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A comprehensive experimental and theoretical study of linear photophysical properties, such as excited-state relaxation, two-photon absorption, and stimulated emission spectra of the symmetrical fluorene derivative 2,2′-((1E,1′E)-(9,9-diethyl-9H-fluorene-2,7-diyl)bis(ethene-2,1-diyl))bis(1-methyl-1H-pyrrole) (1), is presented. The steady-state absorption, fluorescence, excitation, and excitation anisotropy spectra of 1 in organic solvents of different polarities are investigated experimentally and modeled. The fluorescence solvatochromism of 1 suggests the occurrence of symmetry breaking in the first excited state. The nature of fast relaxation processes in the excited state of 1, with the characteristic times of several picoseconds, is investigated by transient absorption femtosecond pump–probe spectroscopy. The spectral properties of 1 are satisfactorily described by an essential-state model that, accounting for electron–vibration coupling and for polar solvation, addresses spectroscopic features not on...

The electronic nature of 4-hydroxy-1H-pyrrolo[3,4-c]pyridine-1,3,6(2H,5H)-trione (HPPT) was comprehensively investigated in liquid media at room temperature using steady-state and time-resolved femtosecond transient absorption spectroscopic techniques. The analysis of the linear photophysical and photochemical parameters of HPPT, including steady-state absorption, fluorescence and excitation anisotropy spectra, along with the lifetimes of fluorescence emission and photodecomposition quantum yields, revealed the nature of its large Stokes shift, specific changes in the permanent dipole moments under electronic excitation, weak dipole transitions with partially anisotropic character, and high photostability. Transient absorption spectra of HPPT were obtained with femtosecond resolution and no characteristic solvate relaxation processes in protic (methanol) solvent were revealed. Efficient light amplification (gain) was observed in the fluorescence spectral range of HPPT, but no super-luminescence and lasing phenomena were detected. The electronic structure of HPPT was also analyzed with quantum-chemical calculations using a DFT/B3LYP method and good agreement with experimental data was shown. The development and investigation of new pyrrolo[3,4-c]pyridine derivatives are important due to their promising fluorescent properties and potential for use in physiological applications.