Dataset Information

Excited-State Proton Transfer of Phenol Cyanine Picolinium Photoacid.

ABSTRACT: Steady-state and time-resolved fluorescence techniques as well as quantum-mechanical calculations were used to study the photophysics and photochemistry of a newly synthesized photoacid-the phenol cyanine picolinium salt. We found that the nonradiative rate constant k _nr of the excited protonated form of the photoacid is larger than that of the excited-state proton transfer (ESPT) to the solvent, k _ESPT. We estimate that the quantum efficiency of the ESPT process is about 0.16. The nonradiative process is explained by a partial trans-cis isomerization reaction, which leads to the formation of a "dark" excited state that can cross to the ground state by nonadiabatic coupling. Moreover, the ESPT process is coupled to the photo-isomerization reaction, as this latter reaction enhances the photoacidity of the studied compound, as a result of photoinduced charge transfer. To prevent trans-cis isomerization of the cyanine bridge, we conducted experiments of PCyP adsorbed on cellulose in the presence of water. We found that the steady-state fluorescence intensity increased by about a factor of 50 and the lifetime of the ROH band increased by the same factor. The fluorescence intensity of the RO^- band with respect to that of the ROH band was the same as in aqueous solution. This explains why inhibiting the photo-isomerization reaction by adsorbing the PCyP on cellulose does not lead to a higher ESPT rate.

SUBMITTER: Pinto da Silva L

PROVIDER: S-EPMC6641337 | biostudies-literature | 2018 Feb

REPOSITORIES: biostudies-literature

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Publications

Excited-State Proton Transfer of Phenol Cyanine Picolinium Photoacid.

Pinto da Silva Luís L Green Ori O Gajst Oren O Simkovitch Ron R Shabat Doron D Esteves da Silva Joaquim C G JCG Huppert Dan D

ACS omega 20180221 2

Steady-state and time-resolved fluorescence techniques as well as quantum-mechanical calculations were used to study the photophysics and photochemistry of a newly synthesized photoacid-the phenol cyanine picolinium salt. We found that the nonradiative rate constant k nr of the excited protonated form of the photoacid is larger than that of the excited-state proton transfer (ESPT) to the solvent, k ESPT. We estimate that the quantum efficiency of the ESPT proc ...[more]

PMID: 31458515

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Project description:Fluorescent probes that exhibit solvatochromic or excited-state proton-transfer (ESPT) properties are essential tools for the study of complex biological or chemical systems. Herein, the synthesis and characterization of a novel fluorophore that reveals both features, 5-isocyanonaphthalene-1-ol (ICOL), are reported. Various solvatochromic methods, such as Lippert-Mataga and Bilot-Kawski, together with time-dependent density functional theory (TD-DFT) and time-resolved emission spectroscopy (TRES), were applied to gain insights into its excited-state behavior. To make comparisons, the octyloxy derivative of ICOL, 5-isocyano-1-(octyloxy)naphthalene (ICON), was also prepared. We found that internal charge transfer (ICT) takes place between the isocyano and -OH groups of ICOL, and we determined the values of the dipole moments for the ground and excited states of both ICOL and ICON. Furthermore, in the emission spectra of ICOL, a second band at higher wavelengths (green emission) in solvents of higher polarities (dual emission), in addition to the band present at lower wavelengths (blue emission), were observed. The extent of this dual emission increases in the order of 2-propanol < methanol < N,N-dimethylformamide (DMF) < dimethyl sulfoxide (DMSO). The presence of the dual fluorescence of ICOL in these solvents can be ascribed to ESPT. For ICOL, we also determined ground- and excited-state pKa values of 8.4 ± 0.3 and 0.9 ± 0.7, respectively, which indicates a considerable increase in acidity upon excitation. The TRES experiments showed that the excited-state lifetimes of the ICOL and ICON spanned from 10.1 ns to 5.0 ns and from 5.7 ns to 3.8 ns, respectively. In addition, we demonstrated that ICOL can be used as an effective indicator of not only the critical micelle concentration (cmc) of ionic (sodium lauryl sulfate (SLS)) and nonionic surfactants (Tween 80), but also other micellar parameters, such as partition coefficients, as well as to map the microenvironments in the cavities of biomacromolecules (e.g., BSA). It is also pointed out that fluorescence quenching by pyridine can effectively be utilized for the determination of the fractions of ICOL molecules that reside at the water-micelle interface and in the interior spaces of micelles.

Dataset Information

Excited-State Proton Transfer of Phenol Cyanine Picolinium Photoacid.

Publications

Excited-State Proton Transfer of Phenol Cyanine Picolinium Photoacid.

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