IR Carbonyl Research Articles

PdZn/ZrO2+SAPO-34 bifunctional catalyst for CO2 conversion: Further insights by spectroscopic characterization

The present work aims at further investigating a previously studied PdZn/ZrO2+SAPO-34 bifunctional catalyst for CO2 conversion. High activity and selectivity for propane was proved and the results obtained by NAP-XPS measurements and CO adsorption at liquid-nitrogen temperature (LNT) followed by FT-IR spectroscopy are shown. After reduction, we confirmed the formation of PdZn alloy. At LNT, Pd carbonyl IR band shows a peculiar behavior linked to an intimate interaction between PdZn particles, ZnO and ZrO2. The combined system was characterized as fresh, used and regenerated. On the fresh PdZn/ZrO2+SAPO-34 the characteristic features of the two components do not appear perturbed by the mixing. As for the used system, the absence of Pd carbonyls and the decrease of CO on SAPO-34 Brønsted acid sites are correlated to organic species revealed by ssNMR. Regeneration in oxygen restores catalytic sites, although new Pd2+/Zn2+ carbonyls appear due to ion exchange into SAPO-34 framework.

Heterometallic Ru–Ir carbonyl clusters as catalyst precursors for hydrogenation and hydrogen transfer reactions

Heterometallic Ru–Ir hydride carbonyl clusters were synthesized and tested as catalyst precursors for hydrogenation of 4-fluoroacetophenone and trans-cinnamaldehyde.

Spectroscopic and electrochemical comparison of [FeFe]-hydrogenase active-site inspired compounds: Diiron monobenzenethiolate compounds containing electron-donating and withdrawing groups

The novel compounds [Fe2(μ-SC6H4-p-NO2)2(CO)6] (1), [Fe2(μ-SC6H4-p-tBu)(μ-SC6H4-p-NO2)(CO)6] (2), [Fe2(μ-SC6H4-p-tBu)2(CO)6] (3), [Fe2(μ-SC6H4-p-tBu)(μ-SC6H4-p-CF3)(CO)6] (4) and [Fe2(μ-SC6H4-p-OCH3)(μ-SC6H4-p-CF3)(CO)6] (5) have been characterized by 1H NMR, FTIR, elemental analysis, and cyclic voltammetry. X-ray crystallography of compounds 1 and 2 reveal an anti (ax,eq) S-aryl ligand orientation in the solid state. Carbonyl IR spectra and reduction potentials correlate strongly with Hammett constants of the electron donating/withdrawing groups. Evaluation for electrocatalytic formation of dihydrogen from acetic acid indicates a low overpotential of activity of 0.26 V for compound 5.

RETRACTED ARTICLE: Revisiting the Evolution of IR Spectra of CO Adsorbed on Au Nanoparticles Supported on Non-reducible Supports

Gold surfaces and nanoparticles have commonly been investigated by IR spectroscopy using carbon monoxide as a molecular probe. An evolution of the IR spectra with time under CO was reported in some cases and tentatively assigned to geometrical effects (e.g. surface reconstruction or particle restructuring) or electronic effects, e.g. gold becoming negatively charged following support reduction. We report here an investigation of the evolution of the IR spectrum of CO adsorbed at 50 °C in the case of Au nanoparticles supported on non-reducible silica and alumina supports. The evolution of the carbonyl IR band signal, proposed to arise mostly from Au particle restructuring, was clearly observed. In addition, the formation of hydrogenocarbonates species on the alumina reemphasized that Au nanoparticles are somewhat active for CO dissociation via Boudouard reaction near room temperature, leading to some deposition of carbon. Water could not prevent restructuring, while O2 prevented irreversibly the reconstruction, which could even be reversed when O2 was introduced on an already restructured sample. It is hypothesized that the role of O2 would be to remove the deposited elemental carbon that otherwise stabilize reconstructed Au. These results emphasize the complexity of the parameters affecting the restructuration of Au surfaces induced by CO and the difficulty in interpreting IR spectra of CO adsorption on Au-based materials.

Cyclic (Aryl)(Amido)Carbenes: NHCs with Triplet‐like Reactivity

AbstractThe synthesis and study of a library of cyclic (aryl)(amido)carbenes (CArAmCs), which represent a class of electrophilic NHCs that feature low calculated singlet‐triplet gaps (ΔEST=19.9 kcal mol−1; B3LYP/def2‐TZVP) and exhibit reactivity profiles expected from triplet carbenes, are described. The electrophilic properties of the CArAmCs were quantified by analyzing their respective selenium adducts, which exhibited the largest downfield 77Se NMR chemical shifts (up to 1645 ppm) measured for any NHC derivative known to date, as well as their Ir carbonyl complexes, from which large Tolman electronic parameter (TEP) values (up to 2064 cm−1) were ascertained. The CArAmCs were found to engage in reactions that are typically observed with triplet carbenes, including C−H insertions, [2+1] cycloadditions with alkenes as well as alkynes, and spontaneous oxidation upon exposure to oxygen.

Cyclic (Aryl)(Amido)Carbenes: NHCs with Triplet-like Reactivity.

The synthesis and study of a library of cyclic (aryl)(amido)carbenes (CArAmCs), which represent a class of electrophilic NHCs that feature low calculated singlet-triplet gaps (ΔEST =19.9 kcal mol-1 ; B3LYP/def2-TZVP) and exhibit reactivity profiles expected from triplet carbenes, are described. The electrophilic properties of the CArAmCs were quantified by analyzing their respective selenium adducts, which exhibited the largest downfield 77 Se NMR chemical shifts (up to 1645 ppm) measured for any NHC derivative known to date, as well as their Ir carbonyl complexes, from which large Tolman electronic parameter (TEP) values (up to 2064 cm-1 ) were ascertained. The CArAmCs were found to engage in reactions that are typically observed with triplet carbenes, including C-H insertions, [2+1] cycloadditions with alkenes as well as alkynes, and spontaneous oxidation upon exposure to oxygen.

Conformational analysis and electronic interactions of some 2-[2’-(4′-substituted-phenylsulfinyl)-acetyl]-5-methylfurans

A conformational study of some 2-[2’-(4′-substituted-phenylsulfinyl)-acetyl]-5-methylfurans 1–4 (OMe1, Me 2, H 3, Cl 4) was performed using IR carbonyl stretching and analysis supported by Natural Bond Orbital (NBO) and Polarisable Continuum Model (PCM) calculations at the B3LYP-D3/aug-cc-pVDZ level, and X-ray diffraction (for 2 and 4). The computational results indicated the existence of four stable conformations with variable degrees of folding (stacking) between the phenyl and the furanyl rings, in the following order of stability: sc(anti)1≫ac(syn)>sc(anti)2 >sc(syn).The PCM data showed that the mean abundance of the most stable lowest frequency sc(anti)1 conformer in vacuum decreases progressively as the solvent permittivity increases, and, concomitantly, the population of the highest νCO frequency sc(anti)2 conformer increases in the same direction. Close inspection to the PCM νCO frequencies and populations of the sc(syn) and ac(syn) conformers suggests that their IR lines should be missed due to their low intensities or hidden under the intense lowest νCO component of the sc(anti)1 conformer. The IR experimental trend observed for the components of the doublet carbonyl band in all solvents just matches the computational results and allows ascribing the most intense lowest νCO frequency and the least intense highest νCO frequency components in CCl4, to the sc(anti)1 and sc(anti)2 conformers, respectively.The appropriate Sδ+(4) … Oδ–(1) short contacts stabilise the four conformers to different extents, while the quasi-parallel Cδ+ = Oδ– and Sδ+ = Oδ– dipole orientations strongly destabilise electrostatically only the sc(anti)2 conformer. This Repulsive Field Effect is also responsible for the increase in its νCO stretching frequency with respect to the other conformers. The suitable β and γ dihedral angles of the anti conformers favour the close proximity of the centroids of the furan and the phenyl rings and the stabilising O(9)[furan] … C(10) [phenyl] short contacts. In contrast, the appropriate geometry adopted by the ac(syn) conformer gives rise to the Oδ–(26) … Hδ+(18) short contact and the LPO(26)→σ*C6–H18 orbital delocalisation (hydrogen bond), which significantly stabilise this conformer with respect to the sc(syn) form.The sum of the delocalisation energies in the NBO analysis does not match the calculated stability of the four conformers for series 1–4. The closeness of the mean delocalisation energy values found for all the conformers suggests that the computed order of stability is controlled mainly by the relevant short contacts and the coulombic repulsions between the negatively charged carbonyl, sulfinyl and furyl oxygen atoms.In particular, the strong electrostatic short contact Oδ–(CO) … Oδ–(SO) repulsion and the half as intense Oδ–(CO) … Oδ–(fur) repulsion destabilise to different extents the sc(anti)2 and the pair of syn conformers, respectively. Therefore, the calculated order of stability of the four conformers for 1–4 results from the overall balance of the orbital and electrostatic interactions. X-ray single crystal analysis of 2 and 4 revealed that the molecules assume an unfolded (stretched) geometry with a sc(syn) conformation, and that they are stabilised through centrosymmetrical C–H(o-Ph) …. O(co) and C–H(m-Ph) …. Cg1(fur) interactions (for 2) and C–H(o-Ph) … O(co) and CPh–Cl … Cg2(Ph) interactions (for 4).

Preparation of hypercrosslinked amine modification resin and its adsorption properties for nitroaromatics

A nitrosation-reduction method had been applied for the modification of DCE-4h. It was a kind of non-polar hypercrosslinked resin and synthesized by our group. The functional resin, NR-07, exhibited good adsorption performance for NACs (Nitroaromatics). The adsorption capacity of NR-07 for p-nitrobenzoic acid was almost 1.3 times as much as that of H-103 in 24h. The adsorption rate of NR-07 calculated by the kinetic function was 1.6 times as much as that of DCE-4h. According to the EA analysis and IR spectrum, the amine and carbonyl group were introduced onto the polymer chains of NR-07. These hydrophilic chemical groups of NR-07 contributed to a higher liquid-film diffusion rate than that of DCE-4h. Besides, the pore volume within 0.46~4.3nm increased after the modification process, which had a positive effect on the intra-particle diffusion process.

Effect of charged and ortho substituents on 17O NMR chemical shifts of substituted phenyl tosylates in DMSO

AbstractThe 17O nuclear magnetic resonance chemical shifts for 31 ortho‐substituted, para‐substituted, and meta‐substituted phenyl esters of 4‐methylbenzenesulfonic acid (phenyl tosylates, 4‐CH3‐C6H4SO2OC6H4‐X) with the neutral and charged substituents in phenoxy part were measured in DMSO‐d6 at 50°C. The chemical shifts, δ(17O), of the sulfonyl (SO2) and single‐bonded phenoxy (O─Ph) oxygens for para and meta derivatives in the case of neutral substituents showed a good correlation with the Taft σI and σ°R substituent constants. The influence of the ortho substituents on the δ(17O) chemical shifts of the sulfonyl oxygens and single‐bonded phenoxy oxygens was found to be described well with the Charton equation: δ(17O)ortho = δ(17O)H + ρI σI + ρRσ°R + δEBs when the data treatment was performed separately for electron‐donating +R substituents and electron‐withdrawing −R substituents. The substituent constants, σ°X±, for the charged substituents (4‐N+(CH3)3I−, 3‐N+(CH3)3I−, 2‐N+(CH3)3I−, 4‐COO−N+Bu4, 3‐COO−N+Bu4, 2‐COO−N+Bu4) calculated from the δ(17O) chemical shifts for phenyl tosylates in DMSO prove that in DMSO, the compounds involving charged substituents are predominantly in ion pair form and not dissociated into free ions. The same conclusion was drawn recently from the carbonyl IR stretching frequencies, νCO, and the carbonyl carbon 13C chemical shifts for substituted phenyl benzoates, C6H5CO2C6H4‐X, in DMSO. It was shown that for ion pairs of the charged substituents in DMSO and concentrated aqueous salt solution, the same substituent constant, σ°X±, could be used.

Conformational analysis of some 4′-substituted 2-(phenylselanyl)- 2-(methoxy)- acetophenones

A conformational study of some 4′-substituited 2-(phenylselanyl)-2-(methoxy)-acetophenones (OMe 1, H 2, and Cl 3) was performed using IR carbonyl stretching band analysis supported by NBO and PCM calculations at the B3LYP/6-31 + G (d,p) level for 1–3 and using X-ray diffraction for 1 and 2. The computational results indicated the existence of three stable conformers for the series (c2, c3, and c1 in order of decreasing stability), whose relative abundance changes with solvent permittivity. The experimental trend observed for the components of the triplet carbonyl band in all solvents matches well with computational results and thus allows for their assignment to distinct conformers. The relative population of the c1 conformer increases in more polar solvents, becoming the most stable conformer in the highest permittivity solvent, acetonitrile, as indicated by IR spectra and PCM calculations. These findings are related to the quasi parallel geometry assumed by the Cδ+ = Oδ− and Cδ+-Oδ- dipoles, which favour stronger solvation. NBO analysis shows that the sum of the energies (ΣE) of the relevant orbital interactions stabilizes the c3 conformer of 1–3 slightly, likely due to the minor contribution of the LPO5→σ*C3Se10 interaction. However, only the c1 conformer is significantly destabilized by the Oδ−(1)CO … Oδ−(5)OMe short contact electrostatic repulsion, which is also responsible for its highest νCO frequency. In addition, the LPO5→ σ*C2C3 orbital interaction accounts for the lowest νCO frequency of c3 conformer. X-ray single crystal analysis of compounds 1 and 2 indicates that in the solid state they assume the least stable c1 conformation found in the gas phase. Molecules of these compounds are stabilized in the crystal through a series of CH⋯O and CH … π intermolecular interactions.

Spectroscopic and theoretical studies of some 2-(2′-haloacetyl)-5-substituted: 1-Methylpyrrole, furan and thiophene

The conformational study of some 2-(2′-haloacetyl)-5-substituted five-membered heteroaromatic compounds Z-CH2C(O)(C4H2X)Y bearing a halogen (Z = Cl or Br) at the 2′-position and (Y = NO2, H, Me or Cl) substituents at the 5-position of the heteroaromatic ring for X = NMe, O and S was performed by IR carbonyl stretching band (νCO) analysis supported by the harmonic frequency, NBO and PCM calculations on the minima and saddle-point structures obtained at the M05-2X/aug-cc-pVTZ level. The computational results predicted the presence of four stable conformers, classified by the orientation of the Xring–CCO (syn/anti) and the OCC–Z (anticlinal/ synperiplanar) moieties as ac(syn), sp(syn), ac(anti) and sp(anti). The anti/syn equilibrium controls the relative stabilities of the conformers to a large extent while the anticlinal/synperiplanar accounts for the observed trend of the IR carbonyl band components. The computed νCO frequencies and the PCM trend of the relative abundance in solvents of increasing permittivity allowed the pairs of ac(syn)/ac(anti) and sp(syn)/sp(anti) conformers to be assigned to the lower and higher νCO frequency IR carbonyl doublet components, respectively. The PCM data failed to reproduce the experimental carbonyl triplet found in chloroform. However, the additional component could be justified by assuming the formation of complexes constituted by one chloroform molecule hydrogen bonded to the conformers in a PCM chloroform continuum.The NBO and short contact analysis suggested that the syn/anti conformational equilibrium is governed mainly by electrostatic interactions, while the anticlinal/synperiplanar depends to different extents on both orbital and electrostatic interactions.

One-Step Synthesis of Mesoporous Silica Thin Films Containing Available COOH Groups.

Inorganic–organic hybrid mesoporous silica thin films with covalently bonded carboxylic acid groups were synthesized in a one-step procedure, using carboxylic-derivatized alkoxysilanes obtained by photochemical radical thiol-ene addition (PRTEA). The organosilanes were synthesized by clicking mercaptosuccinic or mercaptoacetic thioacids with vinyltrimethoxysilane, using benzophenone as the photoradical initiator. The films were synthesized by evaporation-induced self-assembly of a sol containing a mixture of tetraethoxysilane and different quantities of the organosilanes, without any further treatment after the PRTEA reaction. Two nonionic surfactants were used as templates to produce different pore sizes. Different aging times were also applied. Structural characterization with electron microscopy, porosimetry measurements, and small angle X-ray scattering with two-dimensional detection demonstrated the obtention of mesoporous phases whose degree of ordering depended on the amount of added organosilane. The incorporation of the functional silanes was shown by X-ray photoelectron spectroscopy, and the presence of the COOH groups was confirmed by Fourier transform infrared (FTIR). Finally, the availability of the COOH groups for further chemical modification was demonstrated by FTIR by following the changes in the typical carbonyl IR bands during proton exchange and metal complexation. The proposed simple methodology allows obtaining COOH-modified silica thin films in one step, without the need of hard reaction conditions or deprotection steps. Functionalization with carboxyl groups brings a pH-dependent switch-ability to the pore surface that can be used for multifunctional mesoporous materials design.

Isolation and Elucidation of 15-Acetylguanacone from Soursop (<i>Annona muricata</i> Linn) Fruit and Molecular Docking Experiments

Annona muricata (Soursop) has attracted attention due to its content of annonaceous acetogenins, a large family of naturally occurring polyketides isolated from various species of the genus Annonaceae. The ethyl acetate fraction of Annona muricata was subjected to standard isolation protocol-gradient and isocratic silica gel column chromatography- to obtain three waxy and whitish amorphous compounds, 002/A1, 002/A2 and 002/C. The structure of compound 200/A2 was elucidated using 1H-NMR spectroscopy, infrared spectroscopy and electron impact (EI+) mass spectroscopy. The molecular weight of 200/A2 was determined as 662 by EI-MS ([M+H]+ : m/z = 662.1) leading to the molecular formula C39H66O8 as obtained using high resolution MS. The existence of an α, β-unsaturated γ-lactone moiety, non-hydroxylated at the C-4 position, was suggested by an IR carbonyl absorption at 1735.9 cm-1 and 1662.7 cm-1; the IR also gave signal for hydroxyl group at 3339.0 cm-1. The presence of a characteristic vinyl proton δ 7.24 (H-35, d), which is characteristic for α, β- unsaturated γ-lactone was confirmed by the 1H-NMR spectrum. The compound was thus elucidated to be 15-acetyl guanacone, an acetogenin. This acetogenin has not been reported in Annona muricata previously. The compound was subsequently subjected to molecular docking experiments which revealed that it targets and binds to vascular endothelial growth factor 2, VEGF2 (-8.5kcal/mole) and α1 β2 integrin (-6.8kcal/mole), This thus suggests that 15-acetyl guanacone prevents metastasis and invasion by cancer cells, and ultimately initiates apoptosis.Key words: VEGF2; Integrin; Cancer; Acetogenins; Apoptosis; Soursop.

Rotational barriers in five related amides

Interest in the low carbonyl IR frequency of 2-hydroxy-N,N-bis(2-hydroxyethyl)acetamide (2) initially prompted our interest in the amide rotational barrier of this molecule and four related amides that present a variety of hydrogen-bonding possibilities. In the course of this study, a previously incorrect structural assignment was established as N,N-bis[2-(acetyloxy)ethyl]-acetamide (6). In acetonitrile-d3, the carbonyl IR frequencies of the five amides were all essentially normal amide frequencies. Despite very different hydrogen-bonding possibilities in the five amides, no clear trends emerged in the comparison of the rotational barriers (ΔG‡), and the rotational barriers were essentially normal for amides. The rotational barrier of 2 did not vary over one order of magnitude difference in concentration.

New Acetylenic Amine Derivatives of 5,8-Quinolinediones: Synthesis, Crystal Structure and Antiproliferative Activity

Acetylenic amine derivatives of the 5,8-quinolinedione were synthesized and characterized by the 1H and 13C NMR, IR spectroscopy and MS spectra. Additionally, the 6- and 7-substituted allylamine-5,8-quinolinediones were synthesized for comparison purposes. The crystal structure was determined for the 6-chloro-7-propargylamine-5,8-quinolinedione and 7-chloro-6-propargylamine-5,8-quinolinedione. Additionally, the IR spectral analysis supplemented by the density functional theory (DFT) calculations were carried out. It was found that different positions of the propargylamine side chain had a distinct influence on crystal structure, formation of H-bonds and the carbonyl stretching IR bands. Correlation between the frequency separation Δν of the carbonyl IR bands and the position of the 6- and 7-substituents was found. The 7-substituted derivatives exhibited a higher frequency separation Δν. The observed correlation could provide an opportunity to use the IR spectroscopy to study substitution reactions. Cytotoxic activities against three human cancer cell lines for the 5,8-quinolinedione derivatives with different amine substituents, i.e., propargylamine, N-methylpropargylamine, 1,1-dimethylpropargylamine, allylamine and propylamine were also analysed with respect to their molecular structure.

Hydrogen Addition to (pincer)IrI(CO) Complexes: The Importance of Steric and Electronic Factors

(POCOP)IrI(CO) [POCOP = κ3-C6H3-2,6-(OPR2)2 for R = tBu, iPr] and (PCP)IrI(CO) [PCP = κ3-C6H3-2,6-(CH2PR2)2 for R = tBu and iPr] complexes can add hydrogen via two distinct pathways. When R = tBu, (POCOP)Ir(CO) and (PCP)Ir(CO) complexes only add hydrogen via a proton-catalyzed pathway due to steric effects, yielding trans-dihydride complexes. For R = iPr, both systems oxidatively add hydrogen to give cis-dihydride complexes which thermally isomerize to more thermodynamically favorable trans-dihydride species, consistent with previous reports. Proton-catalyzed hydrogen addition pathways are also observed for both iPr-substituted (pincer)Ir(CO) complexes. (PCP)Ir(CO) complexes add hydrogen under milder conditions than the analogous POCOP species. Intermediate hydrido-pyridine Ir(III) carbonyl complexes from the proton-catalyzed pathway have been synthesized and characterized. This is the first report of a series of complexes shown to add hydrogen via concerted oxidative addition or a proton-catalyzed pathwa...

Developing a Modern Approach To Account for Steric Effects in Hammett-Type Correlations.

The effects of aryl ring ortho-, meta-, and para-substitution on site selectivity and enantioselectivity were investigated in the following reactions: (1) enantioselective Pd-catalyzed redox-relay Heck reaction of arylboronic acids, (2) Pd-catalyzed β-aryl elimination of triarylmethanols, and (3) benzoylformate decarboxylase-catalyzed enantioselective benzoin condensation of benzaldehydes. Through these studies, it is demonstrated that the electronic and steric effects of various substituents on selectivities obtained in these reactions can be described by NBO charges, the IR carbonyl stretching frequency, and Sterimol values of various substituted benzoic acids. An extended compilation of NBO charges and IR carbonyl stretching frequencies of various substituted benzoic acids was used as an alternative to Hammett values. These parameters provide a correlative tool that allows for the analysis of a much greater range of substituent effects because they can also account for proximal and remote steric effects.

Insight into the stereoelectronic parameters of N-triphos ligands via coordination to tungsten(0).

A series of new N-triphos tungsten complexes have been synthesised and structurally characterised. The coordination behaviour of a range of N-triphos (N(CH2PR2)3, NP3(R)) ligands, and a mixed-arm diphosphine-pyridyl (PPN(Cyh)) ligand were explored. The steric and electronic parameters of five N-triphos ligands: NP3(Ph), NP3(iPr), NP3(Cyp), NP3(Cyh) and NP3(PhF2), and the carbon-centred triphos ligand, CH3C(CH2PPh2)3 (MeCP3(Ph)), were established. Steric parameters were evaluated by analysing the cone angles calculated from X-ray crystal structures, whilst the electron-donating ability of the ligands was determined from (31)P-(77)Se NMR coupling constants of selenium derivatives and the IR carbonyl stretching frequencies across a series of tungsten-carbonyl complexes. In general, electron-rich phosphines formed bidentate complexes while less electron-rich ligands coordinated in a tridentate mode, regardless of steric bulk. An indirect interaction between the apical nitrogen of the ligand and metal centre is implicated for tridentate complexes and is supported through DFT calculations and analysis of N-protonated complexes. Complexes 1, 3, 4, 6-8 and 10 were characterised by single-crystal X-ray crystallography.

Diverse Cation-Promoted Reactivity of Iridium Carbonyl Pincer-Crown Ether Complexes

Several new iridium(I) and iridium(III) carbonyl complexes supported by aminophosphinite pincer ligands have been prepared and characterized. A surprising diversity of reaction pathways was encountered upon treatment of Ir carbonyl complexes with Li+, Na+, Ca2+, and La3+ salts. Iridium(III) hydridocarbonyl chloride complexes underwent either halide abstraction or halide substitution reactions, whereas iridium(I) carbonyl complexes underwent protonative oxidative addition reactions. When the nitrogen donor of the pincer ligand is an aza-crown ether macrocycle, cation–macrocycle interactions could be supported, leading to divergent reactivity in some cases.

Photochemical stability of dicyano‐substituted poly(phenylenevinylenes) with different side chains

ABSTRACTThe photodegradation mechanism study has been conducted on poly(2,5‐dioctyl‐1,4‐phenylene‐1,2‐dicyanovinylene) (C8‐diCN‐PPV) and poly[2,5‐bis(decyloxy)−1,4‐phenylene‐1,2‐dicyanovinylene] (ROdiCN‐PPV) to understand the reason behind the faster photodegradation of C8‐diCN‐PPV which has a lower LUMO. In both polymers, radical superoxide anion mechanism, which is responsible for electron‐rich RO‐PPVs, is found to be energetically unfavorable for both diCN‐PPVs due to diCN substitution. The IR analysis results confirm this and suggest that singlet oxygen (O2) is the main culprit for photodegradation of both polymers, which cleaves the CC bonds into carboxylic acids. The rates of MW reduction (by GPC) and increase in carbonyl IR absorption intensity are in excellent agreement for both polymers. Phosphorescence study indicates that the faster photodegradation of C8‐diCN‐PPV is due to intersystem crossing, which helps generate singlet O2 upon photoexcitation. No phosphorescence was detected in RO‐diCN‐PPV, suggesting that inefficient intersystem crossing makes RO‐diCN‐PPV photochemically more stable. This work shows that a small difference in side chain structure can lead to a significant difference in photochemical stability. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 2820–2828