Extended Fluorescence Lifetime Research Articles

Quantum chemistry − guided design of luminescent Triphenylene − based co-crystals: Unveiling heavy atom for enhanced fluorescence lifetime

This study employed quantum chemical methods to predict and synthesize three luminescent cocrystals. Utilizing Triphenylene as the electron donor and 1,2,4,5-tetracyanobenzene (TCNB), 2,3,5,6-tetrafluoroterephthalonitrile (TFP), and 2,3,5,6-tetrachloroterephthalonitrile (TCP) as acceptors, the structures and internal interactions of these cocrystals were analyzed. The predominant interactions observed were charge transfer, hydrogen bonding, and π-π interactions. Notably, the Triphenylene-TCP cocrystal exhibited a significantly extended fluorescence lifetime compared to the other two. Further investigations, employing time-dependent density functional theory (TD-DFT) on Triphenylene-TCP, suggested that intersystem crossing (ISC) and reverse intersystem crossing (RISC) mechanisms contribute to the prolonged fluorescence lifetime. This study offers valuable insights into the design of supramolecular cocrystals to enhance the performance of organic fluorescent materials.

Unveiling the Carrier Dynamics of Perovskite Light-Emitting Diodes via Transient Electroluminescence.

Perovskite light-emitting diodes (PeLEDs) have garnered significant attention due to their outstanding optoelectronic properties. However, investigating carrier transport and recombination behavior during device operation poses persistent challenges. In this study, we explore the impact of additive and interface engineering on device performance using transient electroluminescence (TREL). Polyethylene glycol (PEG) induces the formation of square-faceted nanocrystals with a homogeneous size distribution and extended fluorescence lifetime. Consequently, these PeLEDs exhibit remarkable stability. Additionally, employing an electron transport layer of 2,4,6-tris[3-(diphenylphosphino)phenyl]-1,3,5-triazine (PO-T2T), which has a better match to the energy bands of the perovskite layer and a higher carrier mobility, allows for lower turn-on voltage and faster response but also suffers from a short decay time and poor stability. Moreover, low-temperature TREL characterization shows that the carrier mobility is also significantly suppressed with decreasing temperature, which reduces the transient response speed.

Effectively enhancing red fluorescence strategy and bioimaging applications of carbon dots

Red-emitting carbon dots have attracted much attention because of their excellent fluorescence properties. It is of great significance to synthesize red-emitting carbon dots with high fluorescence quantum yield. Herein, by using citric acid and 1,8-diaminonaphthalene as precursors in N, N-dimethylformamide, novel carbon dots (NC-CDs) exhibiting red emission at 607 nm upon excitation at 514 nm were synthesized via a solvent-thermal approach. NC-CDs aggregated in lipid droplets of cells, and hemin quenched their fluorescence. Subsequently, cationic surfactants cetyltrimethylammonium bromide, anionic surfactants sodium dodecyl sulfate and nonionic surfactants were used to functionalize the NC-CDs. The results indicated that both ionic surfactants increased the fluorescence quantum yield and solubility of NC-CDs with extended fluorescence lifetime. This approach is applicable to a class of carbon dots that possess both carboxyl and amino groups. Additionally, these functionalized NC-CDs exhibited high recognition sensitivity towards ClO− and Cu2+ respectively except for hemin. This study provides a novel approach for the synthesis of highly red-emitting carbon dots, expanding their applications in the field of biological imaging and sensing. The findings hold significant implications for the real-time monitoring of hemin in lipid droplets. Additionally, this work offers a simple method to dramatic enhance their fluorescence quantum yield.

β-Bi2O3-Bi2WO6 Nanocomposite Ornated with meso-Tetraphenylporphyrin: Interfacial Electrochemistry and Photoresponsive Detection of Nanomolar Hexavalent Cr.

Hexavalent chromium exposure via inhalation, ingestion, or both has been proven to adversely affect internal organs, induce toxic effects, cause allergies, and contribute to the development of cancer. It requires a substantial and challenging effort to detect several heavy metal ions conveniently, sensitively, and reliably by using materials that are easy to synthesize and have a high yield. The impact of light on the electrocatalytic oxidation/reduction process proves an environmentally friendly methodology with numerous applications in pollution control. The extensive use of photoactive materials in photoelectrochemical (PEC) sensors necessitates the development of stable and highly effective photoactive materials. Hence, the solvothermal synthesis of the organic-inorganic hybrid nanocomposite β-Bi2O3-Bi2WO6/H2TPP with varying weight percentages of meso-tetraphenylporphyrin (H2TPP) resulted in a selective electrode for electrocatalytic and photoelectrocatalytic reduction of Cr6+ on fluorine-doped tin oxide (FTO) by an adsorption-reduction mechanism. H2TPP increases the active site density and provides an effective surface area for efficient adsorption by providing both pyridinic- and pyrrolic-N atoms to β-Bi2O3-Bi2WO6/H2TPP. H2TPP could effectively adsorb Cr6+ in the β-Bi2O3-Bi2WO6/H2TPP composite system through electrostatic interaction, and the adsorbed Cr6+ ions were reduced to trivalent chromium Cr3+, resulting in promising Cr6+ sensing. The projected density of states and Bader charge calculations result in the electrostatic attraction among the N-2p orbital of H2TPP and the 3d and 4s orbitals of the Cr atom, resulting in the adsorption of the hexavalent Cr atom onto the active center of H2TPP. Moreover, the addition of H2TPP results in the development of a mesoporous surface that offers strong electrical conductivity, a substantial surface area, improved charge-mass transport, intimate contact between the electrolyte and catalyst, an extended fluorescence lifetime, and increased stability. The role of pH values was thoroughly investigated. All electrochemical and photoelectrochemical studies were carried out on 5 wt % H2TPP-ornated β-Bi2O3-Bi2WO6. Nanocomposite β-Bi2O3-Bi2WO6/5 wt % H2TPP demonstrated reliable cyclic stability, reproducibility, good sensitivity (8.005 μA mM cm-2), and a low limit of detection (LOD) (8.0 nM) toward photoelectrocatalytic reduction of Cr6+. The interference study in the presence of a few inorganic entities exhibited excellent selectivity. This tale amplification approach for developing a β-Bi2O3-Bi2WO6/5 wt % H2TPP nanocomposite system suggests a deeper understanding of the application of photoelectrocatalytic reduction of Cr6+ in environmental remediation with real samples under light irradiation.

Doable production of highly fluorescent, heteroatom-doped graphene material from fuel coke for cellular bioimaging: An eco-sustainable cradle-to-gate approach

The manifold usage of fluorescent materials and their pliable association with optical imaging techniques have made great strides in unfolding the incredible potential of biotechnological research, particularly in cancer treatment, from point-of-care assay to clinical applications. Enlarged nuclei or numerous counts often indicate tumor growth activity, and these expressions can be visualized with the aid of fluorescence imaging. Therefore, developing highly fluorescent, biocompatible, and sustainable biomarkers for imaging is a vital necessity for their extensive application in cancer diagnosis and therapy. In this work, we have demonstrated the ‘cradle-to-gate’ transformation of abundant and cheap fossil fuel coke into a fluorescent probe for bioimaging. Herein, for the first time, a facile strategy for modulating the emission characteristics of coke-derived graphene system via doping of heteroatoms has been reported. It is found that the doping of nitrogen atoms could strongly influence photophysical properties, giving rise to increased quantum yield (16%), extended fluorescence lifetime (8.51 ns), and higher photostability (92%). Moreover, the as-synthesized nitrogen-doped graphene derivative is used as a potential labelling agent for the cellular imaging of cancerous cells, as well as normal cells, at concentrations ranging from 0 to 100 μg/mL. For 24h incubation, the cells cultured with a concentration of 25 μg/mL were observed to have an appreciable fluorescence accompanied by significant biocompatibility, with a viability value of ≥85%. Considering the heteroatom-induced emission characteristics and bioanalytical acuities, it is prospective that the coke-derived graphene system can be further explored to elucidate its significance in biomedical applications, without compromising on economic and environmental sustainability.

Human Serum Albumin Binds Native Insulin and Aggregable Insulin Fragments and Inhibits Their Aggregation.

The purpose of this study was to investigate whether Human Serum Albumin (HSA) can bind native human insulin and its A13–A19 and B12–B17 fragments, which are responsible for the aggregation of the whole hormone. To label the hormone and both hot spots, so that their binding positions within the HSA could be identified, 4-(1-pyrenyl)butyric acid was used as a fluorophore. Triazine coupling reagent was used to attach the 4-(1-pyrenyl)butyric acid to the N-terminus of the peptides. When attached to the peptides, the fluorophore showed extended fluorescence lifetimes in the excited state in the presence of HSA, compared to the samples in buffer solution. We also analyzed the interactions of unlabeled native insulin and its hot spots with HSA, using circular dichroism (CD), the microscale thermophoresis technique (MST), and three independent methods recommended for aggregating peptides. The CD spectra indicated increased amounts of the α-helical secondary structure in all analyzed samples after incubation. Moreover, for each of the two unlabeled hot spots, it was possible to determine the dissociation constant in the presence of HSA, as 14.4 µM (A13–A19) and 246 nM (B12–B17). Congo Red, Thioflavin T, and microscopy assays revealed significant differences between typical amyloids formed by the native hormone or its hot-spots and the secondary structures formed by the complexes of HSA with insulin and A13–A19 and B12–B17 fragments. All results show that the tested peptide-probe conjugates and their unlabeled analogues interact with HSA, which inhibits their aggregation.

CdSe/CdS/CdTe Core/Barrier/Crown Nanoplatelets: Synthesis, Optoelectronic Properties, and Multiphoton Fluorescence Upconversion.

Colloidal two-dimensional (2D) nanoplatelet heterostructures are particularly interesting as they combine strong confinement of excitons in 2D materials with a wide range of possible semiconductor junctions due to a template-free, solution-based growth. Here, we present the synthesis of a ternary 2D architecture consisting of a core of CdSe, laterally encapsulated by a type-I barrier of CdS, and finally a type-II outer layer of CdTe as so-called crown. The CdS acts as a tunneling barrier between CdSe- and CdTe-localized hole states, and through strain at the CdS/CdTe interface, it can induce a shallow electron barrier for CdTe-localized electrons as well. Consequently, next to an extended fluorescence lifetime, the barrier also yields emission from CdSe and CdTe direct transitions. The core/barrier/crown configuration further enables two-photon fluorescence upconversion and, due to a high nonlinear absorption cross section, even allows to upconvert three near-infrared photons into a single green photon. These results demonstrate the capability of 2D heterostructured nanoplatelets to combine weak and strong confinement regimes to engineer their optoelectronic properties.

Conformationally restrained pentamethine cyanines and use in reductive single molecule localization microscopy.

Pentamethine cyanines are a class of far-red fluorophores that find extensive use in single-molecule localization microscopy (SMLM), as well as a broad range of other techniques. A drawback of this scaffold is its relatively low quantum yields, which is due to excited state deactivation via trans-to-cis chromophore isomerization. Here we describe a synthetic strategy to improve the photon output of these molecules. In the key synthetic transformation, a protected dialdehyde precursor undergoes a cascade reaction that forms a tetracyclic ring system. The resulting conformationally restrained analogs exhibit improved fluorescence quantum yield and extended fluorescence lifetimes. These properties, together with their ability to efficiently recover from hydride reduction, enable a uniquely simple form of single-molecule localization microscopy (SMLM).

Synthesis of Anisotropic CdSe/CdS Dot-in-Giant-Rod Nanocrystals with Persistent Blue-Shifted Biexciton Emission

Anisotropic single-phase wurtzite CdSe/CdS nanocrystals were synthesized by colloidal chemistry, introducing ZnCl2 to increase the shell growth in the radial direction. As a result, dot-in-giant-rod nanocrystals were obtained, with a core diameter that varied between 3.2 and 7.5 nm and an overall diameter between 15 and 22 nm, corresponding to a 14–26 ML CdS shell. In addition to an extended fluorescence lifetime, typical for CdSe/CdS heteronanocrystals, all samples also yielded a blue-shifted biexciton emission peak. This contrasts with existing data on CdSe/CdS dot-in-rod nanocrystals with a thin shell, which yield a type-I band offset and attractive biexciton interactions for CdSe/CdS with a core larger than about 2.8 nm. However, k·p calculations support the blue shift, with a significant electron delocalization into the CdS shell even for large core diameter. We assign this effect to the influence of strain at the CdSe/CdS interface and associated reduction of the conduction band offset, as well as the buildup of a piezoelectric field along the nanorod long axis. The strain-induced electron–hole separation is particularly effective in large-core nanocrystals, providing a tool to engineer electron and hole wave functions that is complementary to quantum confinement.

Synthesis of B←N embedded indacenodithiophene chromophores and effects of bromine atoms on photophysical properties and energy levels

Developing novel fused π-conjugated chromophores has been an energetic research realm and knowing how to adjust their photophysical properties and energy levels through structure tailoring is of pivotal importance. Herein, based on the ladder-type π-conjugated indacenodithiophene (IDT) moiety, four B←N embedded IDT structures, namely, BNIDT, BNIDT-2Br, BNIDT-4Br, and BNIDT-6Br are synthesized and fully characterized. The influences of B←N unit embedded in the IDT backbone and Br atoms anchoring at the periphery on the photophysical properties and energy levels are discussed systematically. From IDT to BNIDT, a new intra-molecular charge transfer (ICT) transition band appears at lower energy (400–600 nm) in the absorption spectra with reduced optical bandgaps (Eg) from 3.25 eV to 2.11 eV and the fluorescence emission peaks red-shift from 390 nm to 565 nm along with remarkably extended fluorescence lifetimes from 1.2 ns to 12.4 ns due to the introduction of electron-deficient B←N into the backbone. Further anchoring Br atoms at the periphery of the backbone gives rise to depressed optical bandgaps, decreased fluorescence quantum yields (Φ), and shortened fluorescence lifetimes (τ) from BNIDT (Eg = 2.11 eV, Φ = 0.46, τ = 12.4 ns), BNIDT-2Br (Eg = 2.08 eV, Φ = 0.18, τ = 4.9 ns), BNIDT-4Br (Eg = 1.67 eV, non-emission) to BNIDT-6Br (Eg = 1.61 eV, non-emission). The HOMO and LUMO levels estimated from ultraviolet photoelectron spectroscopy (UPS) and optical bandgaps also experience synergetic lowering from IDT to BNIDT-6Br. This work indicates that backbone modification with electron-deficient B←N unit and side groups tailoring with halogen atoms are powerful to manipulate the optical properties and energy levels of fused π-conjugated chromophores.

Water-soluble, neutral 3,5-diformyl-BODIPY with extended fluorescence lifetime in a self-healable chitosan hydrogel.

3,5-Diformyl-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (3,5-diformyl-BODIPY) can be used as an efficient biofunctional cross-linker to generate a new class of chitosan-based hydrogels with fluorescence resonance energy transfer (FRET) dynamics and good solubility in water. The hydrogel was fully characterized by FT-IR, UV-vis, fluorescence, FE-SEM, AFM, rheology and picosecond time-resolved spectroscopic techniques. The self-healing ability was demonstrated by rheological recovery and macroscopic and microscopic observations. The fluorescence lifetime was found to increase in aqueous solution of the BODIPY-chitosan hydrogel compared to the 3,5-diformyl-BODIPY monomer. Calculations based on experimental results such as red-shift and decreased intensity of the emission spectrum of highly dye-concentrated hydrogel in comparison to dilute hydrogels, together with changes in the fluorescence lifetime of the hydrogel at different concentration of dyes, suggest that the BDP-CS hydrogels fluorescence dynamics obey the Förster resonance energy transfer (FRET). Improvements in mechanical and photochemical properties and the acceptable values of BODIPY fluorescence lifetime in the hydrogel matrix indicate the utility of the newly synthesized hydrogels for biomedical applications.

Trans-Stilbenoids with Extended Fluorescence Lifetimes for the Characterization of Amyloid Fibrils.

It was previously reported that two naphthyl-based trans-stilbene probes, (E)-4-(2-(naphthalen-1-yl)vinyl)benzene-1,2-diol (1) and (E)-4-(2-(naphthalen-2-yl)vinyl)benzene-1,2-diol (3), can bind to both native transthyretin (TTR) and misfolded protofibrillar TTR at physiological concentrations, displaying distinct emission maxima bound to the different conformational states (>100 nm difference). To further explore this amyloid probe scaffold to obtain extended fluorescence lifetimes, two new analogues with expanded aromatic ring systems (anthracene and pyrene), (E)-4-(2-(anthracen-2-yl)vinyl)benzene-1,2-diol (4) and (E)-4-(2-(pyren-2-yl)vinyl)benzene-1,2-diol (5), were synthesized employing the palladium-catalyzed Mizoroki–Heck reaction. (E)-4-Styrylbenzene-1,2-diol (2), 3, 4, and 5 were investigated with respect to their photophysical properties in methanol and when bound to insulin, lysozyme, and Aβ1-42 fibrils, including time-resolved fluorescence measurements. In conclusion, 4 and 5 can bind to both native and fibrillar TTR, becoming highly fluorescent. Compounds 2–5 bind specifically to insulin, lysozyme, and Aβ1-42 fibrils with an apparent fluorescence intensity increase and moderate binding affinities. The average fluorescence lifetimes of the probes bound to Aβ1-42 fibrils are 1.3 ns (2), 1.5 ns (3), 5.7 ns (4), and 29.8 ns (5). In summary, the variable aromatic moieties of the para-positioned trans-stilbenoid vinyl-benzene-1,2-diol with benzene, naphthalene, anthracene, and pyrene showed that the extended conjugated systems retained the amyloid targeting properties of the probes. Furthermore, both the anthracene and pyrene moieties extensively enhanced the fluorescence intensity and prolonged lifetimes. These attractive probe properties should improve amyloid detection and characterization by fluorescence-based techniques.

Channeling Exciton Migration into Electron Transfer in Formamidinium Lead Bromide Perovskite Nanocrystal/Fullerene Composites.

Hydrophobically capped nanocrystals of formamidinium lead bromide (FAPbBr3 ) perovskite (PNC) show bright and stable fluorescence in solution and thin-film states. When compared with isolated PNCs in a solution, close-packed PNCs in a thin film show extended fluorescence lifetime (ca. 4.2 μs), which is due to hopping or migration of photogenerated excitons among PNCs. Both fluorescence quantum efficiency and lifetime decrease in a PNC thin film doped with fullerene (C60 ), which is attributed to channeling of exciton migration into electron transfer to C60 . On the other hand, quenching of fluorescence intensity of a PNC solution is not accompanied by any change in fluorescence lifetime, indicating static electron transfer to C60 adsorbed onto the hydrophobic surface of individual PNCs. Exciton migration among close-packed PNCs and electron transfer to C60 places C60 -doped PNC thin films among cost-effective antenna systems for solar cells.

Channeling Exciton Migration into Electron Transfer in Formamidinium Lead Bromide Perovskite Nanocrystal/Fullerene Composites

AbstractHydrophobically capped nanocrystals of formamidinium lead bromide (FAPbBr3) perovskite (PNC) show bright and stable fluorescence in solution and thin‐film states. When compared with isolated PNCs in a solution, close‐packed PNCs in a thin film show extended fluorescence lifetime (ca. 4.2 μs), which is due to hopping or migration of photogenerated excitons among PNCs. Both fluorescence quantum efficiency and lifetime decrease in a PNC thin film doped with fullerene (C60), which is attributed to channeling of exciton migration into electron transfer to C60. On the other hand, quenching of fluorescence intensity of a PNC solution is not accompanied by any change in fluorescence lifetime, indicating static electron transfer to C60 adsorbed onto the hydrophobic surface of individual PNCs. Exciton migration among close‐packed PNCs and electron transfer to C60 places C60‐doped PNC thin films among cost‐effective antenna systems for solar cells.

Incorporating a piperidinyl group in the fluorophore extends the fluorescence lifetime of click-derived cyclam-naphthalimide conjugates.

Ligands incorporating a tetraazamacrocycle receptor, a ‘click’- derived triazole and a 1,8-naphthalimide fluorophore have proven utility as probes for metal ions. Three new cyclam-based molecular probes are reported, in which a piperidinyl group has been introduced at the 4-position of the naphthalimide fluorophore. These compounds have been synthesized using the copper(I)-catalyzed azide-alkyne Huisgen cycloaddition and their photophysical properties studied in detail. The alkylamino group induces the expected red-shift in absorption and emission spectra relative to the simple naphthalimide derivatives and gives rise to extended fluorescence lifetimes in aqueous buffer. The photophysical properties of these systems are shown to be highly solvent-dependent. Screening the fluorescence responses of the new conjugates to a wide variety of metal ions reveals significant and selective fluorescence quenching in the presence of copper(II), yet no fluorescence enhancement with zinc(II) as observed previously for the simple naphthalimide derivatives. Reasons for this different behaviour are proposed. Cytotoxicity testing shows that these new cyclam-triazole-dye conjugates display little or no toxicity against either DLD-1 colon carcinoma cells or MDA-MB-231 breast carcinoma cells, suggesting a potential role for these and related systems in biological sensing applications.

Highly differentiated fluorescence quenching of hemoglobin using a stilbazolium dye

In this article, we reported here an effective and selective sensing of hemoglobin (Hb) with a stilbazolium dye, HNEP+. The nature of the HNEP+/Hb interaction was examined using a combination of various spectroscopic techniques. Complexation induced selective fluorescence quenching with a large Stern–Volmer constant, Ksv, the origin of which is attributed to the neutral isoelectric point (pI) of the proteins. The stoichiometry of the DNEP+:Hb was determined to be 1:2 by a Job's plot analysis, and the induced circular dichroism measurements revealed a loss of the α-helix and the unfolding of the proteins in the complex. The addition of cyclodextrin extended fluorescence lifetime, which ensured the accuracy and repeatability of the measurements. Finally, by taking advantage of a subtle change in pI and subsequently Ksv of the glycated Hb, HbA1c, we suggested the possibility of a new sensing concept for HbA1c. The current investigation demonstrates that a selective optical response of a stilbazolium dye can find significant usefulness in bio-sensing applications.

Energy transfer mechanisms among various laser dyes co-doped into gel glasses

Abstract Various dyes mixtures consisting of perylene red (P-red), pyrromethene 567 (PM567) and coumarin dyes are incorporated into vinyltriethoxysilane (VTES)-derived gel glasses, respectively. Energy transfer processes among dyes are investigated by measuring the time-resolved and steady-state emission spectra, and fluorescence lifetime of each dye. The energy transfer mechanisms are discussed with 4 categories of dye pairs and extended fluorescence lifetime of PM567 and P-red are observed. The radiative and non-radiative nature of the energy transfer processes and their dependence on the donor dye concentration are estimated, paving the way for highly efficient, stable and broadly tunable solid-state dye laser materials.

Mitochondrial NADH Fluorescence Is Enhanced by Complex I Binding

Mitochondrial NADH fluorescence has been a useful tool in evaluating mitochondrial energetics both in vitro and in vivo. Mitochondrial NADH fluorescence is enhanced several-fold in the matrix through extended fluorescence lifetimes (EFL). However, the actual binding sites responsible for NADH EFL are unknown. We tested the hypothesis that NADH binding to Complex I is a significant source of mitochondrial NADH fluorescence enhancement. To test this hypothesis, the effect of Complex I binding on NADH fluorescence efficiency was evaluated in purified protein, and in native gels of the entire porcine heart mitochondria proteome. To avoid the oxidation of NADH in these preparations, we conducted the binding experiments under anoxic conditions in a specially designed apparatus. Purified intact Complex I enhanced NADH fluorescence in native gels approximately 10-fold. However, no enhancement was detected in denatured individual Complex I subunit proteins. In the Clear and Ghost native gels of the entire mitochondrial proteome, NADH fluorescence enhancement was localized to regions where NADH oxidation occurred in the presence of oxygen. Inhibitor and mass spectroscopy studies revealed that the fluorescence enhancement was specific to Complex I proteins. No fluorescence enhancement was detected for MDH or other dehydrogenases in this assay system, at physiological mole fractions of the matrix proteins. These data suggest that NADH associated with Complex I significantly contributes to the overall mitochondrial NADH fluorescence signal and provides an explanation for the well established close correlation of mitochondrial NADH fluorescence and the metabolic state.

Bright monomeric red fluorescent protein with an extended fluorescence lifetime

Fluorescent proteins have become extremely popular tools for in vivo imaging and especially for the study of localization, motility and interaction of proteins in living cells. Here we report TagRFP, a monomeric red fluorescent protein, which is characterized by high brightness, complete chromophore maturation, prolonged fluorescence lifetime and high pH-stability. These properties make TagRFP an excellent tag for protein localization studies and fluorescence resonance energy transfer (FRET) applications.

Energy migration in conjugated polymers: the role of molecular structure

Conjugated polymers undergo facile exciton diffusion. Different molecular structures were examined to study the role of the excited state lifetimes and molecular conformations on energy transfer. There is a clear indication that extended fluorescence lifetimes give enhanced exciton diffusion as determined by fluorescence depolarization measurements. These results are consistent with a strong electronic coupling or Dexter-type energy transfer as the dominating mechanism. The control of polymer conformations in liquid crystal solvents was also examined and it was determined that more planar conformations gave enhanced energy transfer to emissive low band-gap endgroups.