Substituent Effect on the Photoreduction Kinetics of Benzophenone

Abstract

The kinetics of the photoreduction of four benzophenone derivatives by isopropyl alcohol was examined in acetonitrile, namely tetra-meta-trifluoromethyl-, di-para-trifluoromethyl-, di-paramethoxy benzophenone and for comparison the unsubstituted molecule itself. The basic spectroscopic (absorption and phosphorescence spectra) and photophysical (quantum yields, excited state energies) properties were established, and the key kinetic parameters were determined by the laser flash photolysis transient absorption technique. The rate coefficients of both the primary and secondary photoreduction reaction show remarkable dependence on ring substitution. This substantial effect is caused by the considerable change in the activation energy of the corresponding process. The experimental results as well as DFT quantum chemical calculations clearly indicate that these benzophenone derivatives all react as n-π* excited ketones, and the rate as well as the activation energy of the reduction steps change parallel with the reaction enthalpies, the determining factor being the stability of the forming aromatic ketyl 2 radicals. The secondary photoreduction of benzophenones by the aliphatic ketyl radical formed in the primary step occurs via a hydrogen bonded complex. The binding energy of the hydrogen bonded complex between the aliphatic ketyl radical reactant and a solvent molecule is a critical parameter influencing the observable rate of the secondary photoreduction.

Daylight-driven rechargeable antibacterial and antiviral nanofibrous membranes for bioprotective applications

“…As shown in Fig. 2I , the T 1 states of BA-RNM, BD-RNM, and BDCA-RNM exhibited obvious electron deficiency character on the oxygen atom in the carbonyl group compared with the ground state, implying the high tendency for hydrogen abstraction ( 35 , 41 ). In contrast, a slight increase of ESP in carbonyl oxygen was observed for CA-RNM, resulting in the inactive T 1 states.…”

“…The BA-RNM shows an obvious absorption peak shift from 262 to 252 nm, characteristic of the formation of reduced moieties in diphenylmethanol (DPM) form (fig. S11) ( 41 ). Meanwhile, besides the DPM formation, a distinct absorption increase was observed at 420 nm for BD-RNM, indicating the formation of a metastable transient photoproduct that was previously referred as the light-absorbing transient (LAT) moieties (fig.…”

First Steps in Photophysics. I. Fluorescence Yield and Radiative Rate Coefficient of 9,10-Bis(phenylethynyl)anthracene in Paraffins

“…5 with Bakhshiev 16 cavity field correction results practically the same datum while other models lead to quite different numbers (see Table 3). 33 , 9,10-dicyanoanthracene (DCNA), 9,10-dimethylanthracene (DMeA), 9,10-dimethoxyanthracene (DMeOA), 9,10-diphenylanthracene (DPhA), ) c small changing value…”

“…In complex processes, such as ours, however, there is no single barrier and the Arrhenius or empirical activation energy can be negative. Yet, this quantity is often used for comparison and interpretation of reactions in related systems 33 ).…”

Direct grafting-from of PEDOT from a photoreactive Zr-based MOF – a novel route to electrically conductive composite materials

“…Usually, iron(III) salts or other oxidizing agents are used for the oxidative polymerization of EDOT. 67 However, the photo-oxidative potential of irradiated benzophenone is well-known in literature [68][69][70] and presents a possible route to oxidative polymerization of EDOT to PEDOT without the necessity for other oxidizing agents (which are not present in our system). The polymerization of EDOT in its neat state without prior attachment to the MOF surface cannot be ruled out, but the resulting polymer chains would not be covalently bonded to the MOF crystals and should be removed by the extended extraction performed on the samples.…”