Ground-state Amine Research Articles

Synthesis, characterization and fluorescence study of new polyacrylates containing stilbene

A new urethane acrylic monomer with stilbene in its structure, trans-4-(2-methacryloyloxyethylcarbamoyloxymethyl)stilbene (SUM), was synthesized to be further free radically copolymerized with methyl methacrylate (MMA). The structures of SUM and the resulting copolymer, trans-4-(2-methacryloyloxyethylcarbamoyloxymethyl)stilbene-co-methyl methacrylate (SUMMA) were characterized by 1H NMR, UV–vis and FTIR spectroscopy, differential scanning calorimetry (DSC), TGA and fluorescence spectroscopy. From the 1H NMR spectrum of the formed copolymer, a composition of about 1:2.6 (SUM/MMA) was determined. The photochemical behavior of the stilbene moieties in polymer was investigated in solution (DMF) and in film state comparatively to that of SUM, following the decreasing under UV irradiation of the π–π∗ absorption band characteristic to the trans-isomer in the UV spectra. Morphologic changes in the surface of the polymeric film during the photoisomerization were visualized by means of atomic force microscopy (AFM) and it is proposed that the new formed cone-shaped structures from the irradiated surface to be attributed to J-aggregates. Analysis of fluorescence shows that the stilbene derivatives showed both monomer emission at 358 (SUM) and 357 nm (SUMMA), and excimer (aggregate) emission at 391 and 412 nm (SUM), and at 374 and 398 nm (SUMMA) in solution. Quenching of the active species (SUMMA) by aliphatic amines shows that this process involves an electron transfer from the ground-state amine to excited stilbene, more efficiently being triethylamine.

Dynamics and equilibrium for the formation of fluorescent Lewis acid-base exciplexes and triplexes between 9-aminophenanthrene and aliphatic amines.

The excited singlet states of 9-aminophenanthrene and its N-aminoalkyl derivatives are strongly fluorescent in cyclohexane. Addition of low concentrations of Et(3)N, Pr(2)NH, or PrNH(2) results in a red shift of the emission maximum and moderately decreased fluorescence intensity. Analysis of the fluorescence behavior using a combination of singular value decomposition with self-modeling and kinetic analysis provides evidence for the sequential formation of 1 : 1 (exciplex) and 1 : 2 (triplex) complexes between the excited 9-aminophenanthrene and ground-state alkylamine, both of which are strongly fluorescent. Both the formation and decay of the exciplex and triplex are dependent upon the extent of amine N-alkylation. Rate constants and equilibrium constants for complex formation follow the order 1 degree approximately 2 degree > 3 degree, analogous to that for the formation of ground-state complexes between amines and the soft Lewis base HgBr(2). Similarly, N-aminoalkyl derivatives of 9-aminophenanthrene form intramolecular exciplexes. Excited-state complex formation is attributed to a Lewis acid-base interaction between the excited aminophenanthrene (lone-pair acceptor) and ground-state amine (lone-pair donor). The factors which determine the stability of excited-state Lewis acid-base complexes are characteristic of the specific excited-state acceptor. No universal scale of lone-pair donor strength can be expected to describe the formation of such complexes.

Primary process for the photochemistry of 9,10-dibromoanthracene yielding 9-bromoanthracene in cyclohexane-amine (triethylamine or N, N-dimethylaniline) studied by picosecond laser photolysis

Picosecond laser photolysis of 9,10-dibromoanthracene (DBA) in cyclohexane-amine (triethylamine or N, N-dimethylaniline) leads to the formation of a DBA-amine exciplex between the lowest excited singlet state of DBA and ground state amine. However, during the decrease in the exciplex absorption with time, no accompanying appearance of an absorption band attributable to the DBA radical anion (DBA .−) can be seen. Nanosecond laser photolysis of DBA in cyclohexane-amine also reveals no existence of an absorption band attributable to DBA .−, but its absorption band is clearly seen in acetonitrile-amine (cf. K. Hamanoue, S. Tai, T. Hidaka, T. Nakayama, M. Kimoto and H. Teranishi, J. Phys. Chem., 88 (1984) 4380, K. Hamanoue, T. Nakayama, K. Ikenaga, K. Ibuki and A. Otani, J. Photochem. Photobiol. A: Chem., 69 (1993) 305). In accordance with this, the rate of DBA → 9-bromoanthracene debromination on steady state photolysis in cyclohexane-amine is extremely slow compared with that in acetonitrile-amine. On the basis of these results, it can be concluded that the intermediaate in the amine-assisted DBA → 9-bromoanthracene debromination is DBA .−, but the decomposition of the DBA-amine exciplex into DBA .− and the amine radical cation is strongly affected by the dielectric constant of the pure solvent.

Solvent Effects on the Formation and Decay of an Exciplex between the Lowest Excited Singlet State of 9,10-Dibromoanthracene and Ground-State Amine (N,N-Dimethylaniline or Triethylamine)

Picosecond laser photolysis reveals the formation of an exciplex between the lowest excited singlet state [DBA*(S1)] of 9,10-dibromoanthracene (DBA) and ground-state amine in acetonitrile (CH3CN) and ethanol (EtOH) containing N,N-dimethylaniline (DMA) [and n-heptane (HP) containing DMA or triethylamine (TEA)]. Only in CH3CN−DMA, however, can decomposition of the DBA−DMA exciplex into the DBA radical anion (DBA•-) and the DMA radical cation be seen, indicating very small generation of DBA•- from the DBA−amine exciplex formed in EtOH−DMA and HP−amine (DMA or TEA). Interestingly, no DBA−TEA exciplex is formed in CH3CN and EtOH containing TEA but nanosecond laser photolysis reveals the existence of DBA•- in the former solvent. Furthermore, the rate of DBA → 9-bromoanthracene debromination upon steady-state photolysis in CH3CN−TEA is 1 order of magnitude smaller than that in CH3CN−DMA but 2 or 3 orders of magnitude greater than those in EtOH and HP containing amine. This suggests that diffusion-controlled quenching of DBA*(S1) by TEA in CH3CN and EtOH gives rise to the formation of a nonemissive short-lived encounter complex or ion pair. It thus be concluded that generation of DBA•- from the DBA−amine exciplex or the encounter complex (or the ion pair) is affected by the dielectric constant of a pure solvent.

Electron transfer induced stereoselective cyclization of 2,2-disubstituted dibenzoylmethane to anti-1,2-cyclopropanediol

Irradiation of 2,2-dimethyl-1,3-diphenyl-1,3-propanedione in the presence of triethylamine gave anti-2,2-dimethyl-1,3-diphenyl-1,3-cyclopropanediol as a major product. On the basis of the results obtained, the mechanism involving single electron transfer between the excited diketone and the ground state amine followed by the anion radical rearrangement was proposed. The same cyclized product was also obtained for the reaction with samarium diiodide.

Photopolymerization of Methyl Methacrylate Using 1-(N,N-Bis-Benzoylamino)-4,5-Diphenyl-1,2,3-Triazole as Photoinitiator

Abstract l-(N,N-Bis-benzoylamino)-4,5-diphenyl-1,2,3-triazole (1) was used as the photoinitiator for the polymerization of methyl methacrylate in bulk and in solution. Polymerization in bulk follows the usual free-radical kinetics. The initiation is believed to occur via hydrogen abstraction from monomer or solvent caused by the excited state of 1. Polymerization was found to be remarkably enhanced by the addition of a small amount of triethylamine. This was attributed to the formation of an electron transfer complex between photoactivated 1 and a ground-state amine.

電子移動を経由するフリルの光環元反応におよぼす溶媒効果

Furil underwent an efficient photoreduction to selectively afford furoin in benzene and acetonitrile containing triethylamine. A thermodynamic analysis of the reaction suggests the operation of an electrontransfer mechanism. Small steric effects of tertiary amines used on the quantum yields for the formation of furoin was explained in terms of a loose radical ion pair formed by an electron transfer from the ground-state amine to the excited singlet-state furil. A pronounced charge transfer-type interaction between the amine radical cation and benzene molecules in the solvent cage was proposed to interpret a high reactivity of furil in the nonpolar solvent, benzene.

Amine-assisted photochemical dehalogenation of haloanthracenes (9-halo and 9,10-dihalo compounds) and their triplet formation

Steady-state photolysis of haloanthracenes (XA; 9,10-dichloro, 9,10-dibromo, 9-chloro and 9-bromo compounds) in acetonitrile-amine (triethylamine or N,N-dimethylaniline) causes the consecutive reactions; 9,10-dihalo compounds→9-halo compounds→ anthracene. Although both the lowest excited singlet [1XA(S1)] and triplet [3XA(T1)] states of XA are quenched by amine, the appearance of absorption spectra due to the haloanthracene radical anions (XA-) within the duration of nanosecond pulse excitation indicates that the intermediates for dehalogenation of XA are XA- produced by a diffusion-controlled reaction of1XA(S1) with the ground-state amine yielding the singlet exciplexes [1(XA-amine)*] which decompose rapidly into XA- and the amine radical cations. Moreover, an amine-assisted formation of3XA(T1) has been attributed to the intersystem crossing from1(XA-amine)* to the triplet exciplexes [3(XA-amine)*] followed by decomposition into3XA(T1) and ground-state amine.

Reinvestigation of photochemical debromination of 9,10-dibromoanthracene and 9-bromoanthracene by amine (triethylamine or N,N-dimethylaniline) studied by nanosecond laser photolysis in acetonitrile at room temperature

Abstract From measurements of the fluorescence and triplet—triplet absorption spectra of bromoanthracenes (XA; the 9, 10-dibromo and 9-bromo compounds) in acetonitrile—amine (triethylamine or N,N -dimethylaniline) at room temperature, the lowest excited singlet states [ 1 XA(S 1 )] of XA are found to be quenched by amine with rate constants of the order for that of a diffusion-controlled reaction. Although the lowest excited triplet states [ 3 XA(T 1 )] of XA are also quenched by amine, the triplet quenching rate constants (4.9 × 10 4 -1.1 × 10 5 dm 3 mol −1 s −1 ) are much smaller than those (1.6 × 10 9 –6.2 × 10 9 dm 3 mol −1 s −1 ) obtained with azulene and ferrocene. Since the decrement in reactant absorptions during steady-state photolysis is not affected upon addition of azulene and ferrocene (1 × 10 −4 mol dm −3 ), the appearance of absorption spectra due to the bromoanthracene radical anions (XA .− ) within the duration of nanosecond pulse excitation and their decay rate constants of 2.4 × 10 5 -1.8 × 10 6 s −1 indicate that the intermediates for debromination are XA .− produced by a diffusion-controlled reaction of 1 XA(S 1 ) with ground-state amine yielding the singlet exciplexes [ 1 (XA—amine)*] followed by the decomposition into XA .− and the amine radical cations. Although 1 (XA—amine)* intersystem cross to the triplet exciplexes [ 3 (XA—amine)*] giving rise to an additional formation of 3 XA(T 1 ), no evidence supporting the participation of 3 (XA—amine)* in the debromination as proposed by Soloveichik et al., High Energy Chem., 23 (1989) 281, translated from Khim. Vys. Energii, 23 (1989) 351 is obtained.

Dechlorination of meso-substituted chloroanthracenes (9,10-dichloro and 9-chloro compounds) via their radical anions produced by a diffusion-controlled reaction of the lowest excited single states of chloroanthracenes with ground-state amine (triethylamine or N,N-dimethylaniline) in acetonitrile at room temperature

Steady-state photolysis of XA (9,10-dichloroanthracene and 9-chloroanthracene) in acetonitrile-amine (triethylamine or N,N-dimethylaniline) causes the consecutive reactions (DCA→CA→anthracene), but the rate of dechlorination is not affected upon addition of azulene and ferrocene in spite of quenching of the lowest excited triplet states [ 3 XA(T ) ] of XA by these additives with quenching rate constants of the order for that of a diffusion-controlled reaction

Formation and decay of styrene-amine exciplexes

The formation and decay of the fluorescent exciplexes formed between two styrenes ( trans-1-phenylpropene and trans-1-(4-cyanophenyl)propene) and two trialkylamines (triethylamine and diisopropylethylamine) were investigated using steady state and transient fluorescence measurements. The standard exciplex kinetic scheme has been expanded for the first time to include quenching of a reversibly-formed exciplex by ground state amine. Analysis of the data for the four exciplex systems provides examples of the four possible modes of exciplex formation (reversible and irreversible) and decay (quenched and unquenched). An anticipated, an increase in the driving force for exciplex formation leads to a decrease in the rate constant for exciplex dissociation, while an increase in the steric bulk of the amine leads to a decrease in the rate constant for exciplex quenching by ground state amine.

Picosecond-nanosecond laser photolysis studies on the photochemical reaction of excited benzophenone with 1,4-diazabicyclo[2.2.2]octane in acetonitrile solution: proton abstraction of the free benzophenone anion radical from the ground state amine

Picosecond and nanosecond dynamics of the ion pair produced by the electron transfer reaction between the triplet state benzophenone ( 3BP*) and 1,4-diazabicyclo[2.2.2]octane (DABCO) was investigated by means of transient absorption spectroscopy and laser-induced photoconductivity measurement. It has been revealed that the solvated free anion radical of BP, produced by the rapid ionic dissociation of the ion pair within 2 ns, abstracts proton from the neutral DABCO giving benzophenone ketyl radical, competing with the charge recombination reaction at encounter with DABCO +, decomposition and/or impurity scavenging processes.

PHOTOCATALYSIS, PHOTOREDUCTION, PHOTOOXIDATION AND PHOTOREDOX HYDROGEN TRANSFER REACTIONS OF METALLOPORPHYRINS

Abstract— Hydrogen transfer from tertiary amines to nitroaromatics is photocatalysed by SnIV and GeIV complexes of tetraphenylporphyrin. There are two photochemical steps, one involving hydrogen transfer to the catalyst, and the second being a hydrogen donation from the intermediate formed. The photoredox properties of para‐substituted tin tetraphenyl porphyrin dichlorides can be correlated with the one electron oxidation‐reduction potentials of the porphyrins and of the reduced intermediates. The steady‐state concentration of intermediate and rate of product formation depend also on the electron donor and acceptor properties of, respectively, the amine and nitro‐compound. Fluorescence results indicate that in both photochemical steps excited singlet states of porphyrins are involved and there is evidence for exciplex formation with ground state amine. Acetic anhydride has a cocatalytic effect but does not influence the quenching of porphyrin fluorescence by amine or the quertchirjg of the fluorescence of the intermediate by nitrobenzene.

QUENCHING OF INTRAMOLECULAR AMINE‐HYDROCARBON EXCIPLEX FLUORESCENCE BY WATER

Abstract— The quenching of intramolecular exciplex fluorescence in 2,6‐bis(methylamino)naphtha]ene, (II), 2,6‐bis(/V‐methyl, methylamino)naphthalene, (III) and 2,6‐bis(N‐dimethy], methylamino)naphthalene, (IV) by water was investigated. Exciplex fluorescence intensity decreased continuously with increase in water concentration; while monomer fluorescence intensity remained constant up to 25% of water, followed by a rapid increase in intensity.Absorption spectra showed that specific interaction occurred between water and ground state amine molecules at high concentrations (25% by volume) of water. These observations were interpreted in terms of a static quenching involving the interaction of water with the ground‐state amine and a dynamic quenching involving the interactions of water with the exciplex. Our observations explain the greater efficiency of exciplex‐fluorescence quenching by protic polar solvents.