Nitrobenzene (≥99%
Sigma-Aldrich), cyclohexane (≥99% Sigma-Aldrich), acetonitrile
(≥99.8% Fisher Scientific), and methanol (≥99.8% Fisher
Scientific) were purchased and used without further purification.
UV–visible absorption spectra of nitrobenzene in deionized
water, methanol, acetonitrile, and cyclohexane were recorded using
a SHIMADZU UV-3600i Plus spectrophotometer.
Femtosecond TAS
experiments have been described previously.64 (link) Briefly, femtosecond laser pulses were generated from a regenerative
amplifier seeded by a Ti:sapphire oscillator (Coherent Astrella-HE-USP).
For UV excitation, tunable laser pulses were generated using an optical
parametric amplifier (OPA; Coherent OPerA Solo). Transient absorption
spectra were recorded using a commercial transient absorption spectrometer
(Ultrafast Systems HELIOS Fire) following photoexcitation at 355 nm
(3.49 eV) with pulse energies of 500 nJ at the sample. The broadband
probe beam was created via white-light generation by focusing a small
portion of the 800 nm fundamental beam into a calcium fluoride plate
to give a probing range of 350–650 nm. The relative polarizations
of the pump and probe beam were set at the magic angle of 54.7°.
Nitrobenzene solutions were flowed continuously at 10 mL min–1 through a Harrick flow cell using a liquid diaphragm pump (KNF,
SIMDOS 02). The concentrations and path lengths were selected to give
an absorbance of around 0.3 at 355 nm: 15 mM water (1000 μm),
104 mM cyclohexane (250 μm), 68 mM acetonitrile (250 μm),
and 102 mM methanol (250 μm). NMR studies indicate negligible
aggregation in 15 mM aqueous nitrobenzene. The instrument response
functions were determined by fitting them to solvent-only spectra.
Sigma-Aldrich), cyclohexane (≥99% Sigma-Aldrich), acetonitrile
(≥99.8% Fisher Scientific), and methanol (≥99.8% Fisher
Scientific) were purchased and used without further purification.
UV–visible absorption spectra of nitrobenzene in deionized
water, methanol, acetonitrile, and cyclohexane were recorded using
a SHIMADZU UV-3600i Plus spectrophotometer.
Femtosecond TAS
experiments have been described previously.64 (link) Briefly, femtosecond laser pulses were generated from a regenerative
amplifier seeded by a Ti:sapphire oscillator (Coherent Astrella-HE-USP).
For UV excitation, tunable laser pulses were generated using an optical
parametric amplifier (OPA; Coherent OPerA Solo). Transient absorption
spectra were recorded using a commercial transient absorption spectrometer
(Ultrafast Systems HELIOS Fire) following photoexcitation at 355 nm
(3.49 eV) with pulse energies of 500 nJ at the sample. The broadband
probe beam was created via white-light generation by focusing a small
portion of the 800 nm fundamental beam into a calcium fluoride plate
to give a probing range of 350–650 nm. The relative polarizations
of the pump and probe beam were set at the magic angle of 54.7°.
Nitrobenzene solutions were flowed continuously at 10 mL min–1 through a Harrick flow cell using a liquid diaphragm pump (KNF,
SIMDOS 02). The concentrations and path lengths were selected to give
an absorbance of around 0.3 at 355 nm: 15 mM water (1000 μm),
104 mM cyclohexane (250 μm), 68 mM acetonitrile (250 μm),
and 102 mM methanol (250 μm). NMR studies indicate negligible
aggregation in 15 mM aqueous nitrobenzene. The instrument response
functions were determined by fitting them to solvent-only spectra.
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