Diphenyl Polyenes Research Articles

The Photophysics of Diphenyl Polyenes Analyzed by Their Solvatochromism

The solvent-dependent intensity changes in the first UV/Vis absorption band of the three polyenes DPH, DPHb, and ttbP3 dissolved in a hydrocarbon solvent with temperature allow for the conclusion that, at temperatures above 233 K, the two phenyl groups of DPH are rotated out-of-plane to yield a non-coplanar molecular structure. This leads to the conclusion that DPH becomes increasingly less coplanar as the temperature rises above 233 K. When the phenyl groups rotate out-of-plane, the polarizability decreases, and the energy of the first electronic transition increases by an extra value. Therefore, below 233 K, the correlation lines between the absorption energy of the 0–0 component of the UV/Vis absorption band and the solvent polarizability, as measured by the SP values, show bilinear behavior. The unexpected behavior shown by DPH dissolved in tetrachloro- and dichloromethane is discussed. We dedicate this research as a tribute to the very important contribution to the solvent effect made by Prof. Christian Reichardt and also to his generous and altruistic scientific help that he has always shown.

Comparison of two diphenyl polyenes as acid-sensitive additives during the biodegradation of a thermoset polyester polyurethane coating.

Biochemical hydrolysis and chemical catalysis are involved in the successful biodegradation of polymers. In order to evaluate the potential separation between biochemical and chemical catalysis during the biodegradation process, we report the use of two diphenylpolyenes (DPPs), all trans-1,4-diphenylbutadiene (DPB) and all trans-1,6-diphenylhexatriene (DPH), as potential acid-sensitive indicators in polymers. 1,4-Diphenylbutadiene and DPH (0.1% w/w) were melt-cast successfully with poly(ethylene succinate) hexamethylene (PES-HM) polyurethane (thermoset polyester polyurethane) coatings above 80℃. When these two DPP/PES-HM coatings were exposed to a concentrated supernatant with significant esterase activity resulting from the growth of a recently isolated and identified strain of Tremellomycetes yeast (Naganishia albida 5307AI), the DPB coatings exhibited a measurable and reproducible localized decrease in the blue fluorescence emission in regions below where hydrolytic biodegradation was initiated in contrast with DPH blended coatings. The fluorescence changes observed in the biodegraded DPB coating were similar to exposing them to concentrated acids and not bases. Our experiments resulted in (1) a method to blend DPP additives into thermoset coatings, (2) the first report of the biodegradation of polyester polyurethane coating by N.albida, and (3) demonstration that hydrolytic supernatants from this strain generate acidic region within degrading polyester coatings using DPB as the indicator. Our experiments confirm that N.albida is an active polyester degrader and that DPB is a promising acid sensitive polymer coating additive.

On the first electronic transitions in molecular spectra of conjugated diphenylpolyenes: A reappraisal

The first UV/Vis absorption band of the diphenylpolyenes (DPPn) from one (DPP1) to seven (DPP7) conjugated double-bonds, dissolved in 2-methyltetrahydrofuran, was recorded by slowly lowering down the temperature from 338 to 138 K. By analyzing these spectra under conditions of constant concentration with the aid of the Mulliken-Rieke rule, it is concluded that the molecular structure of these compounds changes significantly when temperature increases.Unlike trans-stilbene (DPP1) and 1,4-diphenylbutadiene (DPP2), which keep up the onset wavelength for the first peak absorption on going from 338 to 77 K, the longer-chain polyenes miss it and generate a weak absorption with an onset that shows up at a longer wavelength – ca. 700 cm−1 to the red. These new onsets cancel out the energy gap between the absorption and emission for these conjugated diphenylpolyenes.

Effect of polyene chain length on the parameters of intra- and intermolecular interactions between all-trans diphenyl polyenes

The parameters of Franck–Condon and Herzberg–Teller interactions that form the fine-structure spectra of all-trans diphenyl polyenes in n-paraffin solutions at 4.2 K are analyzed. The effect the length of a polyene chain has on the emergence of benzene fragment bands is considered for four all-trans-diphenyl polyene compounds that differ by the number of π-conjugated bonds in the polyene chain.

DFT Modeling of Sandwich Complexes Involving Cationic Palladium Chains and Polyenic or Polycyclic Aromatic Hydrocarbons

DFT calculations are reported on a series of one-dimensional palladium complexes with general formula [Pd(m)(C(2n)H(2n+2))(2)](2+) (m = 2-4, n = 2-8, n > or = m), in order to model and analyze the bonding in the series of organometallic sandwich compounds recently reported by the group of T. Murahashi and H. Kurosawa. The bonding interactions are elucidated, and the frontier orbitals involved are described as a function of the haptotropic conformation of the metal atoms, either di-hapto or tri-hapto. In both cases, the driving force to the complex organization is a strong donation interaction from the pi system of the hydrocarbons to an orbital with appropriate phase and composition, delocalized over the metal chain, and depopulated by the double oxidation process. No net bonding interaction can be characterized along the metal string, and the metal-metal distances are mainly governed by the hapticities of adjacent atoms. The energy associated with the formation of a complex is calculated with respect to its fragments, assumed either isolated or solvated. The results emphasize the stabilizing role of a large delocalization of the positive charge transferred to the hydrocarbons. This delocalization extends to the hydrocarbon regions not directly in contact with palladium and highlights the importance of these "inactive" regions in complexes made from diphenyl polyenes or polycyclic aromatic hydrocarbons. Finally, the bonding pattern deduced from calculations has been utilized to consider the feasibility of novel sandwich architectures, whose computed energy balance eventually proves similar to that of already existing compounds.

Dyes included in channels: effects of the confinement on the photoexcited triplets: A TR-EPR study

The photoexcited triplet states of different π-conjugated organic dyes, included in segregating matrices of organic hosts with channel-like cavities, have been studied by time resolved-EPR. The dyes have been studied also in glassy phases and the triplet spectra in different matrices have been compared with each other to study the effects of the confinement on the guest molecules. We studied some nitro-substituted diphenyl polyenes and oligothiophenes as guests in self-assembling inclusion compounds with perhydrotriphenylene or tris-o-phenylenedioxicyclotriphosphazene. We observed three possible effects of the inclusion on the conformations of the guests: a reduced number of conformations due to the geometrical constraints; an increased number of conformations due to the stabilizing host–host interactions; peculiar conformations determined by head-to-tail interactions with the neighbours along the channel.

Calculation of the vibronic spectra and structure of methylstyrene in the excited state by the parametric method

Calculations of the excited-state structure and of the absorption and radiation spectra of trans-β-methylstyrene are performed by the parametric method for models of the first and second approximations. Only three of the parameters, being constant in a series of related compounds, are used for molecular fragments. In the calculation, the main regularities observed in electronic spectra are reproduced, and an analysis and interpretation of their fine vibrational structure are carried out. The use of the model of the second approximation with a single additional parameter allows more accurate reproduction of angular deformations of the molecule under excitation and of the characteristic changes observed in the low-frequency spectral region in the series of diphenyl polyenes, stilbene, styrene, and methylstyrene molecules. It is shown that the parameters of the second approximation (just as of the first one) possess the transference property in the homological series of molecules. In modeling complex molecules in excited states and their vibronic spectra, the parametric method is more efficient than the ab initio one.

Rotational Diffusion and Trans-cis Isomerization of Substituted Diphenyl Polyenes in the Compressible Region of Supercritical Fluids.

We examine rotational diffusion and trans-cis isomerization of two diphenyl polyenes, diphenylbutadiene (DPB) and hydroxymethyl-stilbene (HMS) in supercritical fluid CO2 and ethane. The results of density dependent rotational diffusion measurements are interpreted using a model which we have recently developed for rotational diffusion in compressible fluids. Comparison of DPB and HMS fluorescence lifetimes indicate that the rate of the isomerization reaction of DPB is nearly independent of density while HMS exhibits a strong density dependence in CO2. Analysis of the HMS data using Kramers theory indicates that the density dependence is the result of solvent-solute frictional interactions.

Towards a quantitative characterization photoisomerization rates

Abstract

Ground and excited state hyperpolarizabilities of cis trans and diphenyl polyenes

Calculations of ground- and excited-state polarizabilities and hyper-polarizabilities of cis-, trans- and diphenyl-polyenes have been carried out by means of cubic response theory implemented at the random-phase approxi mation level. The length, frequency and conformational dependences of these quantities are predicted and discussed.

Electron Transfer Reactions within Zeolites: Radical Cation from Benzonorbornadiene

Zeolites are being used as solid acid catalysts in a number of commercial processes. Occasionally zeolites are also reported to perform as electron transfer agents. Recently, we observed that radical cations of certain olefins and thiophene oligomers can be generated spontaneously within ZSM-5 zeolites. We noticed that these radical cations generated from diphenyl polyenes and thiophene oligomers were remarkably stable (at room temperature) within ZSM-5 and can be characterized spectroscopically at leisure. We have initiated a program on electron transfer processes within large pore zeolites. The basis of this approach is that once a cation radical is generated within a large pore zeolite, it will have sufficient room to undergo a molecular transformation. Our aim is to identify a condition under which electron transfer can be routinely and reliably carried out within large pore zeolites such as faujasites. To our great surprise, when benzonorbornadiene A and a number of olefins were included in divalent cation exchanged faujasites. they were transformed into products very quickly (<15 min). This observation allowed us to explore the use of zeolites as oxidants. Results of our studies on benzonorbornadiene are presented in this communication. 16 refs., 1 fig.

Isomerization of Diphenyl Polyenes. Part VIII. Absorption and Fluorescence Properties of l-Phenyl-4-diphenylthiophosphinyl Butadiene in Poly (vinyl alcohol) Film

Abstract The effect of temperature (from 296 to 423 K) upon the absorption and fluorescence of l-phenyl-4-diphenylthiophosphinyl butadiene (PDPB) and of the direct irradiation on the absorbance were investigated in poly(vinyl alcohol) film. It was found that for PDPB in PVA film the transition from cis to trans configuration is only possible as a result of thermal isomerization due to the softening of PVA polymer, whereas photoisomerization results in both cis-to-trans and trans-to-cis transitions. Similar as with 1,4-diphenyl-1,3-butadiene in PVA, the luminescence is due to two, trans-trans and cis-trans, PDPB conformers.

Multiple luminescence from ‘push-pull’ diphenyl polyenes revealed by picosecond spectroscopy. Evidence for TICT and bicimer states

Picosecond time-resolved spectroscopy has been used to study the emission behavior of 1-( p-N,N-dimethylaminophenyl)-4-( p-cyanophenyl)-1,3-butadiene (DCB) and 1-( p-N,N-dimethylaminophenyl)-6-( p-cyanophenyl)-1,3,5-hexatriene (DCH) in different solvents and experimental conditions (temperature, concentration, excitation intensity). At low concentrations ( c < 10 −4 M) in polar solvents, we clearly resolved two emission bands: the first one is attributed to the planar conformer and is the direct precursor of the second one attributed to the emission of a TICT state. At higher concentration ( c > 10 −4 M) and higher excitation intensity a third emission appears, assigned to a ‘bicimer’ species, as observed previously in stilbene derivatives. This βicimer’ species is formed by the association of at least two excited molecules. Under certain experimental conditions, laser action can be observed from the bicimer emission.

Isomerization of Diphenyl Polyenes. Part VII. The effect of Daylight and Direct Irradiation on the Photoisomerization of Ph-(CH = CH)n-Ph for n = 2, 3, 4 in Poly(vinyl alcohol) Films

Abstract Photoisomerization of 1,4-diphenyl-1,3-butadiene (DPB), 1,6-diphenyl-1,3,5-hexatriene (DPH) and 1,8-diphenyl-1,3,5,7-octatetraene (DPO) in poly(vinyl alcohol) (PVA) films was studied unter daylight and direct irradiation. The most efficient photoisomerization occurs in the DPB molecule, the smallest among the compounds investigated. For the greatest, DPO, molecule no distinct isomerization was observed in daylight and only a temperature effect was noted. Therefore, the DPO molecule in the PVA film heated to 423 K may serve as a fluorescence standard.

ChemInform Abstract: Isomerization of Diphenyl Polyenes. Part 4. Evidence for Two Luminescent Conformers of 1,4‐Diphenyl‐1,3‐butadiene in Poly(vinyl alcohol) Films.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Isomerization of Diphenyl Polyenes. Part V. The Origin of Fluorescence of l,6-Diphenyl-1,3,5-hexatriene in Poly (vinyl alcohol) Films

Abstract The effect of temperature on the absorption and fluorescence spectra of l,6-diphenyl-1,3,5-hexatriene (DPH) was investigated in three different polymer films: polyvinyl chloride) (PVCh), polyvinyl formal) (PVF) and polyvinyl alcohol) (PVA) in the temperature range 296-423 K. Anomalous behaviour of the fluorescence intensity was observed only for DPH in non-heated PVA film. The intensity distribution in the fluorescence band of DPH in both non-heated and heated PVCh and PVF films was found to be independent of the excitation light wavelength, λexc . The behaviour of DPH is similar in the PVA film heated to 423 K. For these samples, single exponential fluorescence decay was observed. The behaviour of non-heated DPH samples in PVA is quite different, the intensity distribution and the fluorescence band position depending strongly on λexc and the fluorescence decay being double exponential. It can be inferred that the fluorescence of DPH in a non-heated PVA sample consists of two components, the first originating from the all-trans conformer and the second from the ground-state s-cis conformer.

Effects of two-photon absorption on degenerate four-wave mixing in solutions of diphenyl polyenes

We have observed double-peaked phase-conjugate pulses in the degenerate four-wave mixing of nanosecond laser pulses in solutions of diphenyl polyenes. We attribute this to the superposition of fast and slow gratings, where the slow grating is due to two-photon absorption. This is supported by the results of time delay and polarization experiments as well as evidence of a second spatial harmonic grating.

Comparison of bipolaron-like charge state generation in the oxidative doping of α,ω-dithienyl and α,ω-diphenyl polyenes stabilized by methoxy and methylthio substituents

Several α,ω-dithienyl and diphenyl polyenes substituted with mesomerically interactive methylthio substituents have been synthesized by Wittig condensation. These polyenes can be oxidatively doped with SbCl5 in solution to yield stable bipolaron-like charge states. The methylthio-substituted bipolaron spectra are considerably more red-shifted in the diphenyl polyene series than the methoxy-substituted counterparts, or the methylthiothienyl series. The potential of these states for enhanced non-linear optical response is presented.

Optical limiting in solutions of diphenyl polyenes

The optical-limiting behavior of a series of trans-alpha, omega-diphenyl polyene compounds was observed in solutions of chloroform. The influence of planarity, the substitution of donor and acceptor groups, and the extent of pi-electron delocalization on the nonlinear thresholds of the diphenyl polyenes in an optical-limiting geometry were examined. A saturation effect of optical-limiting nonlinear thresholds, consistent with the theoretical work, was observed at 10-11 pi-electron bonds. The temporal profiles of the transmitted laser pulses and the power dependence of the nonlinear thresholds as a function of spot size and wavelength were examined. These examinations led to the conclusion that the predominant nonlinear mechanism was quasi-steady-state self-focusing. Nonlinear thresholds an order of magnitude lower, and thus effective n(2) and X(3) values an order of magnitude higher, than the well-known self-focusing medium CS(2) were observed. Our studies demonstrate that this series of polyenes consists of efficient broadband nonresonant optical-limiting materials.

Isomerization of Diphenyl Polyenes

We describe an unusual temperature dependence of 1,8-diphenyl-1,3,5,7-octatetraene absorption in poly(vinyl alcohol) films. Upon heating above 80 °C, the optical density (in the long wavelength region) of this compound increases rapidly. A sample heated to 150 °C has a nearly twenty times higher optical density than a non-heated sample. This effect is not reversible: Once the sample is heated it retains its absorbance on cooling to room temperature. In our opinion, the effect has its origin in changes of the chromophore molecules from cis to trans conformation at the high temperature. Possible applications of these unique material properties should be improved temperature sensors, optical data storage, non-developed high resolution photography or typing, etc.