Photophysical Properties and Ultrafast Excited-State Dynamics of a New Two-Photon Absorbing Thiopyranyl Probe

Comprehensive linear photophysical and photochemical characterization, two-photon absorption (2PA) properties, and femtosecond excited-state dynamics of a symmetrical fluorene derivative 2-(2,6-bis((E)-2-(7-(diphenylamino)-9,9-dihexyl-9H-fluoren-7-yl)vinyl)-4H-thiopyran-4-ylidene)malononitrile (1) are reported. The linear one-photon absorption (IPA), steady-state fluorescence, excitation, and excitation anisotropy spectra of 1 were investigated in organic solvents of different polarities at room temperature, exhibiting rather complex absorption and emission behavior. The relatively strong 2PA of thiopyranyl 1 was investigated by the open aperture femtosecond Z-scan technique in the main long wavelength IPA contour with maxima cross sections up to 600-700 GM. Femtosecond dynamics of the excited-state absorption (ESA) and gain processes in 1 exhibited fast complicated relaxation phenomena with a strong dependence on solvent polarity and a weak dependence on excitation wavelength. The nature of the observed transient absorption kinetics was explained based on the short-lived ESA bands of 1 and solvate relaxation phenomena. Quantum chemical calculations, based on density functional theory, were employed for additional analysis of the IPA and 2PA properties of 1.