Quantum Yield In Solution Research Articles

The synthesis and the solvent and substituent effect on the spectroscopic characteristic of 3-ethyl -2-( p-substitued styryl)benzothiazolium iodides

The photophysical and photochemical properties of p-substitued 2-styryl-ethylbenzothiazolium iodides, possessing different electron-withdrawing or electron-donating groups are described. The dyes were prepared by the condensation of 3-ethyl-2-methylbenzothiazole salts with p-substituted benzaldehydes. The synthesis of suitable substrates is presented as well. We describe here the absorption, emission spectra and the luminescence quantum yield of hemicyanine dyes (SH) measured in 11 different organic solvents of varying polarity. Molecular structure of the synthesized dyes was established by 1H NMR, electronic absorption and fluorescence spectrometry. The spectral data confirmed that all the compounds exist in E-configuration of their styryl residues. The planar molecular conformation is typical for the compounds with five-membered side aromatic moieties (for example benzothiazole). The compounds possessing N-alkyl substituent in phenyl ring, in contrast to the compounds with other substituents, exhibit low fluorescence quantum yield in THF solution. This indicates that for N-alkyl derivatives the non-radiative processes are much more effective than the radiative ones. The electronic absorption and fluorescence emission spectra of tested dyes demonstrate high sensitivity to the nature of substituent introduced into the aromatic ring.

High Tg blue emitting materials for electroluminescent devices

A series of 2′,7′-di-tert-butyl-9,9′-spirobifluorene derivatives (flu) incorporating arylamines at the 2- and/or 7-positions were synthesized. These compounds possess a high glass transition temperature ranging from 135 to 215 °C. Incorporation of spirobifluorene was found to be beneficial for raising the glass transition temperature (Tg) of the molecules. Most of the compounds are blue emitting with good solution quantum yields. Blue-emitting double-layer devices with narrow full width at half-maximum (fwhm < 68 nm) were constructed using these materials as the hole-transporting and emitting layer, and TPBI (1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene) as the electron-transporting layer (device I). In double-layer devices of the configuration ITO/flu (40 nm)/Alq3 (40 nm)/Mg : Ag (Alq3 = tris(8-hydroxyquinoline)aluminium) (device II), flu functioned mainly as a hole-transporting layer, and the green light characteristic of Alq3 was detected. Two of the devices of type I have very promising performance, and one of them emits pure blue light (CIE (x,y) = (0.15, 0.09)). One of the compounds was found to be an efficient hole-injection material.

Synthesis and characterisation of soluble aluminium complex dyes based on 5-substituted-8-hydroxyquinoline derivatives for OLED applications

Some new 5-substituted 8-hydroxyquinoline derivatives and their Al(III) complex dyes (Al( 2) 3–Al( 9) 3) have been synthesised. The compounds were characterized by 1H, 13C, mass and elemental analysis. The aluminium complexes retain the spectroscopic properties of the parent compound, namely, tris(8-hydroxyquinolinato) aluminium (III) (AlQ 3). In dichloromethane solution, these aluminium complexes show absorption maxima in the range of 390–395 nm, strong green luminescence in the range 527–536 nm and aluminium complexes show high fluorescence quantum yield in solution and thin films. The fluorescence decay in solution as well as in thin film is fitted to biexponential with τ av ranging from 3 to 9 ns. Electroluminescence (EL) of the spin-cast film of Al( 3) 3 ( 3 = 5-(2-ethylhexyloxymethyl)-8-hydroxyquinoline) as the emitting layer was performed and the turn-on voltage for the EL device is about 11 V.

Arylethynyl Substituted 9,10-Anthraquinones: Tunable Stokes Shifts by Substitution and Solvent Polarity

2-Arylethynyl- and 2,6- and 2,7-diarylethynyl-substituted 9,10-anthraquinones were synthesized via Sonogashira coupling reactions of 2-bromo-, 2,6-dibromo-, and 2,7-dibromo-9,10-anthraquinone with para-substituted phenylacetylenes. While the redox properties of those compounds are almost insensitive to substitution, their absorption maxima are linearly related to the Hammett constants with different slopes for electron donors and electron acceptors. All compounds are photoluminescent both in solution (quantum yields of emission ≤6%), and as solids. The emission spectra have the characteristics of charge-transfer bands with large Stokes shifts (100−250 nm). The charge-transfer character of the emitting state is supported by large dipole moment differences between the ground and the excited state as concluded on the basis of molecular modeling and Lippert−Mataga correlations of the Stokes shifts with solvent polarity. Maximum Stokes shifts are attained by both electron-donating and -withdrawing groups. This...

1,3,6,8‐Tetraphenylpyrene Derivatives: Towards Fluorescent Liquid‐Crystalline Columns?

AbstractTetraphenylpyrene has been selected as a discotic core to promote liquid‐crystalline fluorescent columns in view of its high fluorescence quantum yield in solution and ease of substitution by flexible lateral side chains. The synthesis and characterization of ten new derivatives of pyrene have been carried out; the pyrene core has been substituted at the 1,3,6,8‐positions by phenylene rings bearing alkoxy, ester, thioether, or tris(alkoxy)benzoate groups on the para position; the compounds have been characterized by mass spectrometry and 1H NMR and UV‐vis spectroscopies. In order to generate liquid‐crystalline phases, the nature, number, and size of the side chains as well as the degree of polarity around the tetraphenylpyrene core have been varied. However, the desired liquid‐crystalline behavior has not been observed. The supramolecular order together with the absorption and emission properties in solution and the solid state are discussed and compared to theoretical predictions. Quantum‐chemical calculations rationalize the high solid‐state fluorescence of a tetraphenylpyrene derivative for which the crystal structure has been determined.

Probing of micellar and biological systems using 2-( p-dimethylaminostyryl)benzoxazole : An intramolecular charge transfer fluorescent probe

A new and highly sensitive molecular probe namely, 2-( p-dimethylaminostyryl)benzoxazole (DMASBO) has been employed to follow the micellar aggregation of three commonly used anionic, cationic and neutral surfactants. These are sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB) and Triton X-100 (TX-100), respectively. From the fluorescence characteristics of DMASBO in dioxane–water mixtures and different surfactant concentrations, the effective polarity of micelle–water interfaces (expressed as dielectric constant and E T (30)) and critical micelle concentrations (cmc) have been measured. In addition, the viscosity of the DMASBO’s environment has been determined from comparison of the fluorescence quantum yield in micellar solutions and methanol–glycerol mixtures. The effect of micelles on the protonation constants of both the ground and excited state has also been studied. The spectral studies in micelles as well as in human serum albumin (HSA) reveal that the intramolecular charge transfer emission of DMASBO is an efficient tool for monitoring and exploring the properties of micelles and the hydrophobic interactions in HSA. The location and orientation of DMASBO probe in micelles and HSA have been discussed.

Highly Branched Polyphenylenes with 1,3,5-Triphenylbenzene Fragments via Cyclocondensation of Acetylaromatic Compounds and Ni0-Catalyzed Dehalogenation: Synthesis and Light Emission

Highly branched photoluminescent polyphenylenes (PP) containing 1,3,5-triphenylbenzene (TPB) fragments were prepared via combination of cyclocondensation of acetylaromatic compounds and Ni0-catalyzed dehalogenation. To develop optimal conditions for cyclocondensation of acetylaromatic compounds, we studied a model reaction of 1,3,5-triphenylbenzene formation using different solvents and catalysts. The maximum 85% yield of TPB was achieved using H2SO4 as a catalyst in ethanol−toluene medium at 50 °C for 5 h. Cyclocondensation polymerization of 4,4‘-diacetyl diphenyl ether or 4,4‘-diacetylbenzene in the presence of equimolar amounts of acetophenone (in the optimal conditions with respect to the soluble polymer yield) did not produce photoluminescent PP due to various defects in the polymer chain. Defect-free PP with starlike fragments were synthesized using Ni0-catalyzed polymerization of aromatic bromides obtained by modification of 1,3,5-tri(p-bromophenyl)benzene. The molecular weights of the polymers were 6700 and 8600 Da. The maximum photoluminescence in solution (quantum yield of 96%) was obtained for the highly branched polymer with starlike TPB fragments, bearing no Br or acetyl groups. The PP of this kind also show very bright fluorescence in the solid state under UV irradiation at 360 nm so they can be considered as promising materials for OLED applications.

The role of sidechains in the luminescence of an electroactive polymer

We report here results of luminescence studies on a series of poly(2,5-dialkoxy-1,4-phenylene vinylene) derivatives incorporating an oxadiazole moiety in the conjugated backbone. While there is no difference in the photoluminescence (PL) quantum yield in solution, the photoluminescence intensity of thin films of the polymers shows a strong dependence on the length of the linear dialkoxy sidechains as it is varied from hexyloxy to dodecyloxy. We attribute this to differences in the packing of the chains and the interchain spacings in the polymers. The side group determines the spacing between the conjugated backbones and thereby, its luminescence efficiency. While there is a direct correlation between chain spacing and PL efficiency, the correlation with electroluminescence (EL) efficiency is subtler. A wider separation between the backbone chains, while suppressing formation of bound polaron pairs and thus aiding luminescence, may hinder interchain charge transport, carrier injection or carrier balance. Hence the actual dependence of EL efficiency on the sidechain is an interplay between these two opposing factors.

Photolysis of ozone in aqueous solutions in the presence of tertiary butanol.

The ozone decomposition quantum yield (phi) in millimolar and higher-concentration aqueous tertiary butanol solution is 0.64 +/- 0.05 (observed over a wavelength range from 250 to 280 nm) and rises toward lower tertiary butanol concentrations (phi approximately 1.5 at 10(-5) M at pH 2) on account of the onset of the well-known *OH-radical-induced chain reaction. The destruction of the organic is initiated by hydrogen-atom abstraction through OH radicals which are produced via the reaction of the photolytically generated O(1D) with the solvent water at a quantum yield of phi(*OH) of about 0.1. There is no decomposition of ozone in the dark on the time scale of the photolysis experiment. The efficiency of tertiary butanol destruction with respect to ozone consumption ([O3]0 = 3 x 10(-4) M), defined by the ratio delta[t-BuOH]/delta[O3], termed eta(t-BuOH), is 0.26 at millimolar tertiary butanol concentrations, determined at the stage of essentially complete ozone consumption. It diminishes toward lower tertiary butanol concentrations (delta[t-BuOH]/delta[O3] approximately 0.17 at [t-BuOH]0 = 1 x 10(-4) M). Part of the effect of the ozone, apart from being a source of *OH radicals, rests on the intervention of HO2*/O2*- which is produced in the course of the peroxyl-radical chemistry of the tertiary butanol in this dioxygen-saturated environment and converted into further *OH radical by reaction with ozone. Moreover in this system, organic free radicals and peroxyl radicals react with the ozone. On the basis of the experimental and mechanistic-simulation data, the quantum yield of direct (by hv) ozone cleavage in aqueous solution is estimated at about 0.5.

Sulfonated phthalocyanines: aggregation and singlet oxygen quantum yield in aqueous solutions

The influence of sulfonation degree (n) and central atom nature on singlet oxygen quantum yield (ΦΔ) were studied for a series of sulfonated phthalocyanine metal complexes MPcS n mix . It was found that in DMSO, where the studied dyes exist as monomers, ΦΔ values are independent of number and position of the sulfogroups and are equal to 0.11 ± 0.02, 0.19 ± 0.03, 0.37 ± 0.05, 0.38 ± 0.05 and 0.68 ± 0.10 for the metal-free and Mg , Gd , Al and Zn complexes, correspondingly. However, in aqueous solutions, aggregation of the dyes determines their photochemical activity. Substitution in adjacent to macrocycle 3 and 6 benzene positions interferes with aggregation compared to 4 and 5 positions, presumably due to enhanced steric hindrances in the former case. In the ZnPcS n mix series (n varied from 2 to 4), as an example, the linear relationship between degree of aggregation and ΦΔ indicates that only the monomer fraction of the dye is responsible for singlet oxygen production. For less sulfonated samples the order of activity of the dyes in water is as follows: H 2 PcS n mix &lt; M II PcS n mix &lt; M III PcS n mix which is in contrast to their tendencies to form aggregates.

A novel extended covalent tripod for assembling triple-helical nine-co-ordinated lanthanide(iii) podates: the rational design of a single conformerElectronic supplementary information (ESI) available: tables of molecular peaks obtained by ESI-MS (Table S1), elemental analyses (Table S2), structural data for the lanthanide co-ordination sphere in [Eu(L13)](ClO4)3 (19, Table S3) and paramagnetic 1H NMR shifts (Table S4). Figures showing views of [Eu(L13)]3+ along

The connection of a methyl group to the apical carbon atom of a semi-rigid extended tripod provides the novel podand 1,1,1-tris-{2-[2-(6-diethylcarbamoyl-pyridin-2-yl)-1-ethyl-1H-benzoimidazol-5-ylmethoxy]-ethyl}-ethane (L13). Reaction with lanthanide(III) in acetonitrile produces stable and dynamically inert C3-symmetrical podates [Ln(L13)]3+ (Ln = La–Lu) in which LnIII is nine-co-ordinate in a pseudo-tricapped trigonal prismatic site. Electron-induced nuclear relaxation in the paramagnetic complex [Nd(L13)]3+ shows that the capping carbon atom adopts the exo conformation with the methyl group pointing outside the cavity of the podand. The crystal structure of [Eu(L13)](ClO4)3 confirms the exclusive formation of the exo conformer, which contrasts with the mixture of two endo conformers reported for the non-methylated analogue. Structural analysis combined with photophysical data in [Ln(L13)](ClO4)3 (Ln = La, Eu, Gd, Tb) point to negligible mechanical coupling mediated by the flexible four-atoms aliphatic chains between the apical carbon atom and the unsymmetrical tridentate binding units. However, the exo conformation of the tripod in [Eu(L13)]3+ removes some interactions between the high-frequency CH oscillators and the metal-centred excited electronic levels, thus leading to larger lifetime and improved quantum yield in solution.

Star-like Aromatic Conjugated Polymers and Dendrimers for OLEDs

ABSTRACTHighly branched photoluminescent polyphenylenes (PP) containing 1,3,5-triphenylbenzene (TPB) fragments were prepared via combination of cyclocondensation of acetylaromatic compounds and Ni0-catalyzed dehalogenation. Defect free PP with star-like fragments were synthesized using Ni0-catalyzed polymerization of aromatic bromides obtained by modification of 1,3,5-tri(p-bromophenyl)benzene. The molecular weights of the polymers were 6700, 8600, and 15300 Da. The maximum photoluminescence in solution (quantum yield of 96%) was obtained for the highly branched polymer with star-like TPB fragments, bearing no Br or acetyl groups. The PP of this kind show also very bright fluorescence in a solid state under UV irradiation at 360 nm so they can be considered as promising materials for OLED applications.

2,7-Carbazole-Based Conjugated Polymers for Blue, Green, and Red Light Emission

Light-emitting 2,7-carbazole-based homopolymers and copolymers were prepared by Yamamoto or Suzuki cross-coupling reaction. Poly(N-(2-ethylhexyl)-2,7-carbazole) (PEHC), poly(N-octadecyl-2,7-carbazole) (PODC), and poly(N-(2-ethylhexyl)-2,7-carbazole-alt-4-heptyl-2,5-pyridine) (PCPy) emit blue light while poly(N-(2-ethylhexyl)-2,7-carbazole-alt-2,3-diheptyl-5,8-quinoxaline) (PCQ) and poly(N-(2-ethylhexyl)-2,7-carbazole-alt-3,3‘,4‘ ‘‘,3‘ ‘‘ ‘-tetramethyl-3‘ ‘,4‘ ‘-dihexyl-2,2‘:5‘,2‘ ‘:5‘ ‘, 2‘ ‘‘:5‘ ‘‘,2‘ ‘‘ ‘-quinquethiophene-1‘ ‘, 1‘ ‘-dioxide) (PCPTO) emit green and red light, respectively. The fluorescence quantum yield in chloroform solution ranges from 25% for PCPTO to 83% for PCQ. All these 2,7-carbazole-based polymers do not show any evidence of excimer formation in the solid state. Most of these polymers exhibit a glass transition at ca. 60−70 °C with a degradation temperature above 385 °C. These new polymeric materials should allow the development of efficient blue-, green-, and red-light-emitting ...

The triplet-state lifetime of indole in aqueous and viscous environments: significance to the interpretation of room temperature phosphorescence in proteins.

The interpretation of room temperature phosphorescence studies of proteins requires an understanding of the mechanisms governing the tryptophan triplet-state lifetimes of residues fully exposed to solvent and those deeply buried in the hydrophobic core of proteins. Since solvents exposed tryptophans are expected to behave similarly to indole free in solution, it is important to have an accurate measure of the triplet state lifetime of indole in aqueous solution. Using photon counting techniques and low optical fluence (J/cm(2)), we observed the triplet-state lifetime of aqueous, deoxygenated indole and several indole derivatives to be approximately 40 micros, closely matching the previous reports by Bent and Hayon based on flash photolysis (12 micros; Bent, D. V.; Hayon, E. J. Am. Chem. Soc. 1975, 97, 2612-2619) but much shorter than the 1.2 ms lifetime observed more recently (Strambini, G. B.; Gonnelli, M. J. Am. Chem. Soc. 1995, 117, 7646-7651). However, we have now been able to reproduce the long lifetime reported by the latter workers for aqueous indole solutions and show that it likely arises from geminate recombination of the indole radical cation and solvated electron, a conclusion based on studies of the indole radical cation in water (Bent and Hayon, 1975). The evidence for this comes from a fast rise in the phosphorescence emission and measurements of a corresponding enhanced quantum yield in unbuffered solutions. This species can be readily quenched, and the corresponding fast rise disappears, leaving a monoexponential 40 micros decay, which we argue is the true indole triplet lifetime. The work is put in the context of room temperature phosphorescence studies of proteins.

The study of rate improvement of trichloroethene (TCE) decay in UV system with hydrogen source

The photosensitization of trichloroethene (TCE) in the presence of hydrogen source of surfactant and photosensitizer was investigated. Photolysis experiments were conducted with a Rayonet RPR-200 merry-go-round photoreactor at 253.7 nm. Solutions containing fixed amount of TCE and surfactant Brij 35 were exposed to UV illumination with different concentrations of acetone (ACE). Quantum yield in solution with surfactant Brij 35 and optimum ACE dosage is about 25 times higher than that in Brij 35 alone. However, with an excess ACE dosage, it would act as a light barrier which attenuates the light intensity for TCE photodegradation. A mathematical model is therefore developed for the prediction of TCE photodegradation in Brij 35 solution containing various ACE concentrations, in which the remaining fraction of TCE (C/C0) in the system can be determined. Apart from the direct photodegradation, photosensitization is postulated to be another major pathway contributing to the overall decay.

Synthesis and Properties of Soluble, Strongly Fluorescent Poly(m-Phenylene)s with Pendant Stilbene-Based Chromophores

The nickel-catalyzed dehalogenative coupling of substituted m-dichlorobenzenes afforded a new series of poly(m-phenylene)s with pendant 2,6-bisstilbenyl-N-alkylpyridinium tetrafluoroborate groups. Characterization of polymers was accomplished by viscosimetry, GPC, FT-IR, NMR, X-ray, differential scanning calorimetry, thermomechanical analysis, UV-vis, and luminescence spectroscopy. The polymers were amorphous and showed an excellent solubility being readily soluble at room temperature in THF, chloroform, and chlorobenzene. Their T g values ranged from 96 to 148°C. The polymers with pendant stilbene-based chromophores were strongly fluorescent both in solution and in solid state. Their photoluminescence (PL) spectra showed maxima at 391-410 nm and 445-532 nm in solution and in thin film, respectively. The structure of the alkyl attached to the pyridinium nitrogen influenced remarkably the PL quantum yield of polymers. The most efficient fluorescent polymers obtained were those bearing long chain aliphatic group on this nitrogen. Their PL quantum yield in THF solution was up to 0.65.

A Series of Thienylene/Phenylene-Based Polymers Functionalized with Electron-Withdrawing or -Donating Groups: Synthesis and Characterization

A series of polymers comprising alternating phenylene and thienylene repeating units and with electron-donating or -withdrawing groups attached on thienylene units, i.e., poly[1,4-bis(3-X-2,5-thienylene)phenylene-alt-2,5-dioctyl-1,4-phenylene] (PBTX, X = OMe, H, Cl, Br, CN), has been synthesized and characterized. These polymers are highly fluorescent, among which PBTH shows the highest solution quantum yield, up to 94% relative to quinine sulfate. The absorption and emission peak wavelengths of PBTOMe are bathochromically shifted and band gap (Eg) is lowered by the presence of electron-donating OMe group, in comparison with PBTH. The influence of electron-withdrawing groups, Br, Cl, and CN, on the absorption peak wavelength and Eg, on the other hand, is not so great. Nevertheless, the film of PBTCN shows an emission maximum near to that of PBTOMe due to the strong interchain interactions. The band structures as deduced from electrochemistry give information supporting the optical measurements. The IP of ...

Highly phosphorescent bis-cyclometalated iridium complexes: synthesis, photophysical characterization, and use in organic light emitting diodes.

The synthesis and photophysical study of a family of cyclometalated iridium(III) complexes are reported. The iridium complexes have two cyclometalated (C(**)N) ligands and a single monoanionic, bidentate ancillary ligand (LX), i.e., C(**)N2Ir(LX). The C(**)N ligands can be any of a wide variety of organometallic ligands. The LX ligands used for this study were all beta-diketonates, with the major emphasis placed on acetylacetonate (acac) complexes. The majority of the C(**)N2Ir(acac) complexes phosphoresce with high quantum efficiencies (solution quantum yields, 0.1-0.6), and microsecond lifetimes (e.g., 1-14 micros). The strongly allowed phosphorescence in these complexes is the result of significant spin-orbit coupling of the Ir center. The lowest energy (emissive) excited state in these C(**)N2Ir(acac) complexes is a mixture of (3)MLCT and (3)(pi-pi) states. By choosing the appropriate C(**)N ligand, C(**)N2Ir(acac) complexes can be prepared which emit in any color from green to red. Simple, systematic changes in the C(**)N ligands, which lead to bathochromic shifts of the free ligands, lead to similar bathochromic shifts in the Ir complexes of the same ligands, consistent with "C(**)N2Ir"-centered emission. Three of the C(**)N2Ir(acac) complexes were used as dopants for organic light emitting diodes (OLEDs). The three Ir complexes, i.e., bis(2-phenylpyridinato-N,C2')iridium(acetylacetonate) [ppy2Ir(acac)], bis(2-phenyl benzothiozolato-N,C2')iridium(acetylacetonate) [bt2Ir(acac)], and bis(2-(2'-benzothienyl)pyridinato-N,C3')iridium(acetylacetonate) [btp2Ir(acac)], were doped into the emissive region of multilayer, vapor-deposited OLEDs. The ppy2Ir(acac)-, bt2Ir(acac)-, and btp2Ir(acac)-based OLEDs give green, yellow, and red electroluminescence, respectively, with very similar current-voltage characteristics. The OLEDs give high external quantum efficiencies, ranging from 6 to 12.3%, with the ppy2Ir(acac) giving the highest efficiency (12.3%, 38 lm/W, >50 Cd/A). The btp2Ir(acac)-based device gives saturated red emission with a quantum efficiency of 6.5% and a luminance efficiency of 2.2 lm/W. These C(**)N2Ir(acac)-doped OLEDs show some of the highest efficiencies reported for organic light emitting diodes. The high efficiencies result from efficient trapping and radiative relaxation of the singlet and triplet excitons formed in the electroluminescent process.

Synthesis and characterization of a novel polyester derived from substituted terfluorene

Poly(1,6-hexane-9,9,9′,9′,9″,9″-hexahexyl-7,2′;7′,2″-terfluorene-2,7″-dicarboxylate) (PTFHHC6) has been synthesized and characterized. This polymer exhibits strong emission in the blue range, both in solution (quantum yield of 76%) and in the solid state. Moreover, PTFHHC6 presents some advantages over other polyfluorene derivatives since its solid-state fluorescence spectrum does not show any excimer formation and does not vary upon thermal treatment. Electrochemical measurements have revealed a reversible p-n dopable polymer. This aromatic polyester shows promising optical and electrical properties for the development of blue light-emitting diodes.

Conjugation Length Control in Soluble Poly[2-methoxy-5-((2‘-ethylhexyl)oxy)-1,4-phenylenevinylene] (MEHPPV): Synthesis, Optical Properties, and Energy Transfer

Poly[2-methoxy-5-(($2^{\prime}$-ethylhexyl)oxy)-1,4-henylenevinylene] (MEHPPV) of varying conjugation length was prepared by the selective thermal elimination of one of the substituents in a suitable precursor polymer. The precursor, a dialkoxy poly(1,4-xylylene) derivative with varying amounts of acetoxy and methoxy groups, was prepared by a competitive nucleophilic substitution of the Wessling polyelectrolyte, using methanol and sodium acetate in acetic acid as nucleophiles. Selective thermal elimination(in solution) of the acetate groups alone yielded MEHPPV of varying conjugation lengths. The selective nature of the acetate elimination was confirmed by $^1H$ NMR spectroscopy. As expected, both the absorption and emission maxima of the eliminated samples shifted to the red with increasing conjugation length. While there was very little difference between the absorption spectra of thin film and solutions of MEHPPV-x, there was a significant bathochromic shift in the emission spectra of the thin films when compared to their dilute solution spectra. Additionally, separate emission from the various oligomers, which are occasionally visible in solution, is absent in thin films. Energy transfer from short to longer conjugated segments, within a single polymer chain in solution, was inferred by comparison of the fluorescence spectra of the partially conjugated polymers with those expected from a system where simultaneous independent emission occurs from a similar collection of noninteracting oligophenylenevinylene (OPV)molecules. The latter was calculated assuming a statistically random substitution/elimination process of the precursor in conjunction with the fluorescence spectral data of OPV's reported by previous workers. The extent of energy transfer increases as the average conjugation length increases. Furthermore, unlike in the model oligomers, in the case of polymers the fluorescence quantum yield in solution rapidly decreases with increase in the average conjugation length.