Electronic spectra and excited state dynamics of pentafluorophenol: Effects of low-lying πσ∗ states

Abstract

Multiple fluorine atom substitution effect on photophysics of an aromatic chromophore has been investigated using phenol as the reference system. It has been noticed that the discrete vibronic structure of the S1←S0 absorption system of phenol vapor is completely washed out for pentafluorophenol (PFP), and the latter also shows very large Stokes shift in the fluorescence spectrum. For excitations beyond S1 origin, the emission yield of PFP is reduced sharply with increase in excess vibronic energy. However, in a collisional environment like liquid hydrocarbon, the underlying dynamical process that drives the non-radiative decay is hindered drastically. Electronic structure theory predicts a number of low-lying dark electronic states of πσ(∗) character in the vicinity of the lowest valence ππ(∗) state of this molecule. Tentatively, we have attributed the excitation energy dependent non-radiative decay of the molecule observed only in the gas phase to an interplay between the lowest ππ(∗) and a nearby dissociative πσ(∗) state. Measurements in different liquids reveal that some of the dark excited states light up with appreciable intensity only in protic liquids like methanol and water due to hydrogen bonding between solute and solvents. Electronic structure theory methods indeed predict that for PFP-(H2O)n clusters (n = 1-11), intensities of a number of πσ(∗) states are enhanced with increase in cluster size. In contrast with emitting behavior of the molecule in the gas phase and solutions of nonpolar and polar aprotic liquids, the fluorescence is completely switched off in polar protic liquids. This behavior is a chemically significant manifestation of perfluoro effect, because a very opposite effect occurs in the case of unsubstituted phenol for which fluorescence yield undergoes a very large enhancement in protic liquids. Several dynamical mechanisms have been suggested to interpret the observed photophysical behavior.

Solvent reorganization triggers photo-induced solvated electron generation in phenol

“…The experimental spectrum in aqueous solution has a maximum at 4.59 eV 35,86 while the one in the gas phase possesses few vibronic transitions 35,85 around 4.6 eV (270 mm), indicating that the solvent barely affects the energy-range of the spectra. The calculated spectra show small shifts, depending on the model used, which are within the error of the method.…”

Preparation of Reactive Oligo(p‐Phenylene Vinylene) Materials for Spatial Profiling of the Chemical Reactivity of Intracellular Compartments

“…2016, 28, 3749-3754 www.advmat.de www.MaterialsViews.com The conjugation of the pentafl uorophenol group to π-conjugated molecular structures could affect the photophysical properties of the conjugates due to the perfl uoro effect as well as the π-electron structure of pentafl uorophenol moiety. [ 19 ] Therefore, it is expected that OPV-pfp will exhibit spectra changes followed by the departure of the pentafl uorophenol active ester group during condensation reactions with the amino group. This will make it possible to monitor the reaction process in situ with different biological species in living cells and also profi le the chemical reactivity in subcellular fractions.…”

“…The conjugation of the pentafluorophenol group to π‐conjugated molecular structures could affect the photophysical properties of the conjugates due to the perfluoro effect as well as the π‐electron structure of pentafluorophenol moiety . Therefore, it is expected that OPV‐pfp will exhibit spectra changes followed by the departure of the pentafluorophenol active ester group during condensation reactions with the amino group.…”

Effects of Ring Fluorination on the Ultraviolet Photodissociation Dynamics of Phenol

“…The effect of multiple fluorination of aromatic molecules, culminating in the perfluoro effect, has been the subject of research interest for many years. [41][42][43][44][45][46] The changes upon progressive fluorination of aromatic molecules manifest, among other ways, in the loss of detailed structure in UV absorption spectra, 42 in the reduction of fluorescence yields alongside shortened lifetimes, 43,45 and, in the case of phenol, in a significant increase in acidity. 44 One of the fundamental changes contributing to these effects is the preferential stabilization of σ orbitals relative to π orbitals by multiple fluorine substituents.…”

“…41 In pentafluorophenol (PFP), this leads to low-lying 1 πσ* states with C−F σ* character, which may fundamentally change the response of the molecule following absorption of UV light. 45 This paper reports new H Rydberg Atom Photofragment Translational Spectroscopy (HRA-PTS) results following photoexcitation of several different fluorophenols at many different UV wavelengths in the range 220    275 nm and draws comparisons between these molecules and with bare phenol itself. To study the effects of substituent location, the photodissociations of 2and 3-fluorophenol (2FP and 3FP respectively) have been investigated, and results compared with existing data on 4-fluorophenol (4FP).…”