Total Internal Reflection Fluorescence Spectroscopy for Investigating the Adsorption of a Porphyrin at the Glass/Water Interface in the Presence of a Cationic Surfactant Below the Critical Micelle Concentration

Electrochemical monitoring of the fluorescence emission of tetrazine and bodipy dyes using total internal reflection fluorescence microscopy coupled to electrochemistry

A very sensitive technique where an electrochemical cell is coupled to a total internal reflection fluorescence microscopy setup is described and applied for the first time to the electrochemical monitoring of the fluorescence of organic dyes in solution. It is shown that this setup basically allows both spatial and time resolution for the recorded fluorescence signal as a function of the electrode potential: indeed the variations of the emission intensity are recorded within the diffusion layer for a classical cyclic voltammetry or chronoamperometry experiment inducing the redox conversion of an emissive form into a non emissive one (and conversely). Simultaneously, the variations of the emissive state lifetime are measured to discriminate between a mechanism involving only the conversion into a non emissive form from one involving a quenching between the emitter and the electrogenerated species. The results concerning the investigation of the electrochemical monitoring of the fluorescence properties for two types of original dyes are presented, demonstrating the possibility to switch on and off the emission in a fully reversible way and to investigate in depth the mechanisms associated to this switch.

Excited state structural dynamics and Herzberg-Teller coupling of tetraphenylporphine explored via resonance Raman spectroscopy and density functional theory calculation

Resonance Raman spectra of free-base tetraphenylporphine (TPP) were obtained with 397.9, 416, and 435.7nm excitation wavelengths and density functional calculations were done to elucidate the electronic transitions and the resonance Raman spectra (RRs) of TPP. The RRs indicate that the Franck-Condon region photodynamics for S(0)-->S(4) electronic state is predominantly along the C(m)-ph stretch while that for S(0)-->S(3) electronic state is predominantly along the porphin ring C(beta)C(beta) stretch. Non-totally symmetric vibrational modes were regularly presented in resonance Raman spectra: the shorter the excitation wavelengths were, the stronger intensity the modes had, which can be interpreted in terms of electric dipole transition moments caused by Franck-Condon and Herzberg-Teller coupling. Four non-total symmetry vibrational mode upsilon(52,)upsilon(64), upsilon(97) and upsilon(130) in A(2) irreducible representative of TPP were observed in 397.9, 416 and 435.7nm resonance Raman spectrum. With the shorter wavelength laser excitations at 416 or 397.9nm, the A(2) vibrational modes show more enhanced Raman intensity by comparison with those in the TPP spectrum excited at 435.7nm.