A fundamental aspect in the study of the charge–transfer (CT) organic crystals with ionic or partially ionic ground states is the investigation of the spectroscopic effect of the electron–molecular vibration coupling. 7,7,8,8‐tetracyano‐2,3,5,6‐tetrafluoroquinodimethane (TCNQF4), an electron acceptor much stronger than TCNQ, is an outstanding component of many interesting CT systems. A thorough vibrational analysis of the title compound and of its monomeric radical anion is reported. The analysis is based on the Raman depolarization ratio measurements and on infrared data of solutions of both neutral and ionic species as well as on polarized infrared spectra of oriented crystals of the neutral molecule. The vibrational assignment, completed by a normal coordinate analysis (NCA), brings to the identification of the ionization frequency shifts and to the choice of the fundamentals (b1uν19 and b2uν33) whose frequencies are diagnostic of the degree of charge transfer for a TCNQF4 moiety partner of a CT system...

Charge–transfer organic crystals: Molecular vibrations and spectroscopic effects of electron–molecular vibration coupling of the strong electron acceptor TCNQF4

Atomic force microscopy (AFM) was used to measure the chemical binding force of discrete electron donor−acceptor complexes formed at the interface between proximal self-assembled monolayers (SAMs). Derivatives of the well-known electron donor N,N,N‘,N‘-tetramethylphenylenediamine (TMPD) and the electron acceptor 7,7,8,8-tetracyanoquinodimethane (TCNQ) were immobilized on Au-coated AFM tips and substrates by formation of SAMs of N,N,N‘-trimethyl-N‘-(10-thiodecyl)-1,4-phenylenediamine (I) and bis(10-(2-((2,5-cyclohexadiene-1,4-diylidene)dimalonitrile))decyl) disulfide (II), respectively. Pull-off forces between modified tips and substrates were measured under CHCl3 solvent. The mean pull-off forces associated with TMPD/TCNQ microcontacts were more than an order of magnitude larger than the pull-off forces for TMPD/TMPD and TCNQ/TCNQ microcontacts, consistent with the presence of specific charge-transfer interactions between proximal TMPD donors and TCNQ acceptors. Furthermore, histograms of pull-off forces ...

Direct detection by atomic force microscopy of single bond forces associated with the rupture of discrete charge-transfer complexes.

Reduced graphene oxide (rGO)/CuS/Au composite nanosheets were prepared herein via a two-step approach based on a simple hydrothermal reaction combined with an in situ reduction process. The rGO/CuS/Au composite nanosheets exhibited good peroxidase-like catalytic activity toward the oxidation of a peroxidase substrate 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H2O2. The rGO/CuS/Au composite nanosheets were also utilized as a new surface-enhanced Raman scattering (SERS) substrate, enabling monitoring of the peroxidase-like catalytic reaction on their active surface. The oxidized intermediate of TMB formed during the peroxidase-like reaction was captured and clearly identified by SERS spectroscopy, providing an avenue for quantitative in situ monitoring of the oxidation of TMB. This approach could also be used to directly detect H2O2 with a detection limit of about 2.1 μM.

Synthesis of bifunctional reduced graphene oxide/CuS/Au composite nanosheets for in situ monitoring of a peroxidase-like catalytic reaction by surface-enhanced Raman spectroscopy

The free radical cation of 1,4-diaminobenzene (p-phenylenediamine, PPD+.) has been generated in aqueous solution, wherein it is short-lived, by oxidation of the parent compound with bromine. The same PPD+. radical has also been produced by UV photolysis of the parent at 77 K in an ethanolic glassy matrix. Resonance Raman spectra of the radical and its parent are reported and analysed in detail with the aid of normal coordinate and molecular orbital calculations. Evidence is presented for (PPD+.)2 dimer formation in aqueous solution at room temperature.

Free radical studies by resonance Raman spectroscopy: Chemically and photochemically generated 1,4-diaminobenzene radical cation

The time‐resolved resonance Raman spectra of the first triplet state and the cw resonance Raman spectra of the radical cation are reported for various isotopic derivatives of the N,N,N′,N′‐tetramethyl‐p‐phenylenediamine (TMPD) and of the N,N,N′,N′‐tetraethyl‐p‐phenylenediamine (TEPD). Vibrational assignments and structural implications are discussed. The radical cation spectra are consistent with a semiquinoidal conformation of the ionized species. They are characterized by a significant frequency increase of the in‐phase ν(N–ring) mode with respect to the ground state spectra (Δν≥120 cm−1) and by the high resonance enhancement of various bands assigned to vibrations of the N(alkyl)2 groups, resulting from couplings of these vibrations with modes of the π chromophore. The triplet spectra display almost only bands due to vibrations of the N(alkyl)2 groups, implying that similar couplings take place in the T1 state. Two signals characterize the N–ring–N framework: one is assigned to the Wilson ring mode 9a ...

A. Grofcsik

Papers

Vibrational study of N,N,N′,N′-tetramethyl-p-phenylenediamine and its radical cation