Spectroscopic and Dynamic Properties of Electronically Excited Pendant Porphyrin Polymers with Backbones of Differing Flexibility.

A zinc porphyrin-pendant norbornene polymer with a rigid backbone characterized by a 2:1 E/Z isomeric structure ratio has been synthesized, and its spectroscopic and photophysical properties are examined. Zinc tetraphenylporphyrin, the porphyrin-substituted norbornene monomer, and a previously reported zinc porphyrin-pendant polymer with a flexible polymethylene backbone have been used as comparators. Unlike its flexible counterpart, the rigid norbornene polymer exhibits clear exciton splitting of its Soret band, much more rapid relaxation rates of its excited singlet states, and a very small yield of an unusually short-lived triplet state. Unlike the flexible pendant polymer, which exhibits excimeric S2 fluorescence as a result of chromophore rotation, anti-Kasha emission from the norbornene polymer originates primarily from the unperturbed porphyrin E region. The low triplet yield in the polymer is attributed to greatly increased rates of competing internal conversion within the singlet manifold. Nevertheless, upconverted delayed fluorescence that is quenched by oxygen is observed upon intense steady-state Q-band excitation of degassed polymer solutions, signaling direct triplet involvement. Consistent with the polymer's rigid structure, this biexcitonic process is assigned to ultrafast singlet exciton migration and triplet-triplet annihilation following absorption of a second photon by the small steady-state concentration of polymer triplets.

Nature does not rely on long-lived electronic quantum coherence for photosynthetic energy transfer.

During the first steps of photosynthesis, the energy of impinging solar photons is transformed into electronic excitation energy of the light-harvesting biomolecular complexes. The subsequent energy transfer to the reaction center is commonly rationalized in terms of excitons moving on a grid of biomolecular chromophores on typical timescales [Formula: see text]100 fs. Today's understanding of the energy transfer includes the fact that the excitons are delocalized over a few neighboring sites, but the role of quantum coherence is considered as irrelevant for the transfer dynamics because it typically decays within a few tens of femtoseconds. This orthodox picture of incoherent energy transfer between clusters of a few pigments sharing delocalized excitons has been challenged by ultrafast optical spectroscopy experiments with the Fenna-Matthews-Olson protein, in which interference oscillatory signals up to 1.5 ps were reported and interpreted as direct evidence of exceptionally long-lived electronic quantum coherence. Here, we show that the optical 2D photon echo spectra of this complex at ambient temperature in aqueous solution do not provide evidence of any long-lived electronic quantum coherence, but confirm the orthodox view of rapidly decaying electronic quantum coherence on a timescale of 60 fs. Our results can be considered as generic and give no hint that electronic quantum coherence plays any biofunctional role in real photoactive biomolecular complexes. Because in this structurally well-defined protein the distances between bacteriochlorophylls are comparable to those of other light-harvesting complexes, we anticipate that this finding is general and directly applies to even larger photoactive biomolecular complexes.

Executive Control in Early Childhood as an Antecedent of Adolescent Problem Behaviors: A Longitudinal Study with Performance-based Measures of Early Childhood Cognitive Processes.

Identifying childhood cognitive processes that predict adolescent problem behaviors can help guide understanding and prevention of these behaviors. In a community sample of 313 youth recruited in a small Midwestern city between 2006 and 2012 (49% male, 64% European American), executive control and foundational cognitive abilities were assessed at age 5 in a lab setting with performance-based measures. In adolescence, youth provided self-report of problem behaviors in surveys administered annually between ages 14 and 16. Executive control was negatively associated with externalizing behavior problems and adolescents getting in trouble at school, accounting for foundational cognitive abilities and family background covariates. Executive control had negative, but nonsignificant, associations with internalizing problems and substance use initiation. The findings point to deficits in executive control as a childhood risk factor for later problems and a potential target for preventive interventions.

Immiscible Anionic Gemini Surfactant-Perfluorinated Fatty Acid Langmuir Monolayer Films.

A new member of the N,N,N',N'-dialkyl-N,N'-diacetate ethylenediamine family of anionic gemini surfactants has been synthesized, and its miscibility with the model perfluorocarbon, perfluorotetradecanoic acid (PF), has been investigated in monolayer films at the air-water interface. Thermodynamics of mixing and the accompanying changes in the mixed film structure have been probed using a combination of compression isotherm measurements supported by Brewster angle microscope imaging and X-ray scattering measurements, and results have been compared with those collected for a previously studied, shorter tail chain variant of the surfactant. Thermodynamic measurements showed that the gemini surfactant and perfluorotetradecanoic acid were immiscible, with weak repulsive interactions, manifesting as small positive deviations from ideal mixing, observed between the two film components. Films were highly textured, with micrometer-scale, phase-separated domains readily detectable. Grazing incidence X-ray diffraction measurements showed that the gemini surfactant was disordered in the monolayers, whereas the perfluorocarbon formed discrete crystallites in the disordered matrix. Despite the small deviations from ideal mixing detected in the thermodynamic measurements, the X-ray measurements indicated that the presence of the gemini perturbs the PF crystal lattice from that of pure PF. Finally, X-ray reflectivity measurements showed that the addition of equimolar PF to the gemini monolayer induces a significant increase in the nominal head group thickness of the film, suggesting that interactions between the two surfactants can lead to structural rearrangements of gemini's head group near to the water surface.

Exciton Dynamics of Photoexcited Pendant Porphyrin Polymers in Solution and in Thin Films.

Several new polymers with rotatable zinc porphyrin pendants have been synthesized and their optical spectroscopic and photophysical properties, including upconversion efficiencies, determined in both fluid solution and thin films. Comparisons made with the ß-substituted zinc tetraphenylporphyrin monomers and ZnTPP itself reveal that the yield of triplets resulting from either Q-band or Soret-band excitation of the polymers is surprisingly small. A detailed kinetic analysis of the fluorescence decays and transient triplet absorptions of the substituted monomers and their corresponding polymers reveals that this phenomenon is due to two parallel internal singlet quenching processes assigned to transient intrachain excimer formation. Consequently, the yields of upconverted S2 fluorescence resulting from Q-band excitation in the degassed polymers are significantly diminished in both fluid solution and thin films. Implications of these results for the design of polymer upconverting systems are discussed.

Mixing Behavior in Binary Anionic Gemini Surfactant-Perfluorinated Fatty Acid Langmuir Monolayers.

The miscibility and film structure of mixed Langmuir monolayer films composed of an anionic gemini N,N,N',N'-dialkyl-N,N'-diacetate ethylenediamine surfactant (Ace(12)-2-Ace(12)) with perfluorotetradecanoic acid (C13F27COOH; PF) have been investigated using a variety of thermodynamic and structural characterization methods. The two film components were found to be miscible in monolayers at the air-water interface over a range of compositions and at all but the lowest surface pressures, with attractive interactions occurring between the two components. While pure PF monolayers formed crystalline lattices with hexagonal symmetry and with the surfactant tails oriented normal to the underlying water subphase, the pure gemini surfactant formed amorphous films with little tendency to orient at the subphase. In mixed films with mole ratios of PF:Ace(12)-2-Ace(12) < 2.5, the miscibility of the two components resulted in a nearly complete loss of crystallinity of the PF, though films at higher mole fractions of PF showed some residual crystallinity, albeit with lattice structures that were significantly different from that of pure PF. Miscibility and film structure in this mixed system are discussed in comparison with other mixed gemini surfactant systems in the literature as well as binary mixtures of phospholipids or monomeric fatty acids with PF.

Examining Change in Therapeutic Alliance to Predict Youth Mental Health Outcomes.

OBJECTIVE: To examine the link between therapeutic alliance and youth outcomes. METHOD: The study was conducted at a group-home with 112 youth with a disruptive-behavior diagnosis. Therapeutic alliance was collected routinely via youth and staff report. Outcome data were collected using youth and staff reports of externalizing behavior as well as behavioral incidents occurring during care. Outcome data were collected following intake into services and at 6 and 12 months of care. Data were analyzed to examine (1) if youth behavior problems at intake were predictive of therapeutic alliance and (2) if changes in alliance were predictive of subsequent youth outcomes. These were conducted with a 6-month service-delivery model and replicated with a 12-month model. RESULTS: There was some support for the first hypothesis, that initial levels of youth externalizing behavior would be related to alliance ratings; however, most of the effects were marginally significant. The second hypothesis, that changes in therapeutic alliance would be related to subsequent youth outcomes, was supported for the 6-month model, but not the 12-month model. CONCLUSIONS: Changes in therapeutic alliance may be predictive of youth outcomes during care. Additional research into examining therapeutic alliance trajectories is warranted to improve mental health services for youth.

Validation of the symptoms and functioning severity scale in residential group care.

Tests that measure the emotional and behavioral problems of children and youth are typically not normed and standardized on youth diagnosed with disruptive behavior, particularly those youth in residential care. Yet professional standards mandate that before instruments are used with a specific population the psychometric properties need to be studied and re-established: specifically, psychometric properties, including validity, need to be evaluated (AERA, APA, and NCME, The standards for educational and psychological testing. AERA, Washington, DC, 1999). The purpose of the present study was to assess the validity characteristics of the Symptoms and Functioning Severity Scale (SFSS; Bickman et al., Manual of the Peabody Treatment Progress Battery, Vanderbilt University, Nashville, TN, 2010), a widely used test developed for use in outpatient clinics, with youth in a residential care program. The convergent validity of the SFSS was established with the large correlations (0.78-0.86) with the CBCL. Several binary classification analyses including specificity, area under the receiver operating characteristic curve, positive and negative likelihood ratios, and the Youden Index supported the validity of the SFSS. However, the sensitivity index was somewhat low indicating the test may produce a high level of false negatives. Limitations, future research and implications are discussed.

Correlates of solitary alcohol and cannabis use among American Indian adolescents.

BACKGROUND: Solitary substance use, or using substances while alone, is common among adolescents but understudied. This is the first study to examine solitary substance use among American Indian (AI) adolescents. The objective was to examine correlates of solitary alcohol use and solitary cannabis use that occur within the individual, family, school, peer, and cultural domains of the social ecology. METHOD: Data were from the 2009-2013 Drug Use Among Young American Indians Study, a cross-sectional cohort study. Two sets of hierarchical logistic regressions were conducted to examine solitary alcohol use (getting drunk) among lifetime alcohol users (n = 2082; Mage = 15.12 years; SD = 1.68; 54.2% female) and solitary cannabis use among lifetime cannabis users (n = 2085; Mage = 14.99 years; SD = 1.69; 50.5% female), including adjustment for level of substance involvement. RESULTS: Prevalence of solitary alcohol use among lifetime drinkers was 24.9%. Among lifetime cannabis users, 53.6% reported solitary cannabis use. Regression analyses for solitary alcohol use showed statistically significant positive associations with coping motive, descriptive norms, violent behavior, depression, peer models for use, and (unexpectedly) peer sanctions against use and a negative association with family sanctions against use. Regression analyses for solitary cannabis use showed statistically significant positive associations with coping motive, violent behavior, and peer models for use and a negative association with family sanctions against use. CONCLUSIONS: Solitary alcohol and cannabis use are prevalent among AI adolescents and might, in particular, reflect attempts to cope with adversity. Findings could help guide the development of screening and prevention efforts.

Antecedents, concurrent correlates, and potential consequences of young adult solitary alcohol use.

OBJECTIVE: Research on young adults has found solitary alcohol use to be positively associated with negative emotions, coping motives for drinking, and negative alcohol-related consequences, but most research has been cross-sectional and based on samples of college students. We examined associations across multiple time points within a sample that was diverse with respect to educational status and age. METHODS: A community sample (N = 754, ages 18-26; 56% female) completed surveys at baseline, monthly for 2 years, and at 30-month postbaseline. Multilevel and single-level regression models assessed longitudinal and concurrent associations between solitary drinking and potential correlates, adjusting for frequency of alcohol use. RESULTS: Moderate depressive symptoms at baseline were associated with a greater likelihood of solitary drinking in drinking months in the subsequent 2 years (Adjusted Odds Ratio [AOR] = 2.22, 95% CI [1.54-3.20]). During those 2 years, both depressive symptoms and coping motives were positively concurrently associated with solitary drinking at the between- and within-person level. Although solitary drinking in a particular month had a small and nonsignificant association with negative alcohol-related consequences, the proportion of drinking months that involved solitary drinking was positively associated with negative alcohol-related consequences across months. More solitary drinking during monthly data collection was associated with greater likelihoods of hazardous drinking and moderate depressive symptoms at 30-month follow-up, but these associations were not statistically significant after adjusting for earlier measures of drinking and depressive symptoms. CONCLUSIONS: The findings point to the importance of considering the drinking context when screening and providing treatment for alcohol misuse. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Associations of childhood executive control with adolescent cigarette and E-cigarette use: Tests of moderation by poverty level.

BACKGROUND: Adolescent cigarette smoking has continued to decline, whereas electronic cigarette (e-cigarette) use has increased dramatically among youth. Nicotine use in any form, even at low levels, during adolescence can have adverse consequences, particularly for low-income individuals. To elucidate potential early intervention targets, this study examined childhood executive control (EC), a set of cognitive processes for directing attention and behavior, in relation to adolescent cigarette and e-cigarette onset, testing for differential prediction by poverty level. METHOD: Participants were 313 children (51% female, 64% European American) recruited in a small city in the Midwestern United States beginning in 2006 and then followed into adolescence between ages 14 and 16 years. EC was measured in the laboratory with performance-based tasks when children were age 5 years, 3 months. Self-reports of cigarette onset and e-cigarette onset were obtained in adolescence (Mage = 15.65 years). Overall, 24% of the sample was at or below the poverty line. RESULTS: Cigarette onset was higher in the poverty group (17%) than in the non-poverty (8%) group, but e-cigarette onset did not differ by poverty level (36% poverty versus 38% non-poverty). Multiple group structural equation modeling revealed a statistically significant group difference such that EC ability was a significant negative predictor of e-cigarette onset for poverty but not for non-poverty youth. A similar group difference was evident as a trend for cigarette onset. CONCLUSIONS: Because EC has been shown to be modifiable, early interventions to improve EC for children living in poverty might help prevent adolescent e-cigarette onset.

A systematic review of research on adolescent solitary alcohol and marijuana use in the United States.

BACKGROUND AND AIMS: Alcohol use and marijuana use tend to be social activities among adolescents. Some youth use alcohol or marijuana while alone. This article provides a framework for examining the risk factors for and consequences of solitary alcohol and marijuana use, grounded in a motivational model that emphasizes coping with negative emotions, and provides the first systematic review of research on solitary alcohol and marijuana use among middle school- and high school-aged adolescents in the United States. METHODS: PubMed, PsycINFO and Web of Science were searched. Articles were included if they mention solitary alcohol or marijuana (or illicit drug) use among adolescents aged 12-18 years. Studies on non-human animals, college students, non-English language publications and articles exclusively about solitary tobacco or inhalant use were excluded. Overall, 22 articles were selected. RESULTS: Prevalence of adolescent solitary alcohol and marijuana use was relatively high (e.g. 14% life-time solitary drinking in the general adolescent population), particularly in high-risk subgroups (e.g. 38.8% life-time solitary drinking in a sample of youth recruited from clinical and community settings). Risk factors for solitary alcohol and marijuana use include earlier onset and heavier use, coping motives, negative emotions and positive expectancies about use. Solitary alcohol and marijuana use are prospectively associated with later substance use disorder (SUD) symptoms, diminished academic performance and perceived health. CONCLUSIONS: Approximately 1 in 7 adolescents in the US appear to have engaged in solitary alcohol and marijuana use at some point. It is positively associated with extent of drinking and marijuana use, cop;ing motives, negative emotions, and positive expectancies, as well as subsequent SUD symptoms and poor academic and health-related outcomes.

Prospective Associations of Child Maltreatment Subtypes With Adult Educational Attainment: Tests of Mediating Mechanisms Through School-Related Outcomes.

This study tests a developmental cascades model in which childhood maltreatment is hypothesized to influence adult educational attainment by increasing attention problems and reducing successful school experiences during adolescence. Two path models tested direct and indirect associations of childhood maltreatment with adult educational attainment. Model 1 used three parent-reported subtypes of childhood maltreatment (physical/emotional abuse, sexual abuse, neglect). Model 2 added an agency-reported measure of childhood maltreatment. Both models detected indirect effects of childhood maltreatment subtypes on adult educational attainment through attention and school discipline problems, poor school engagement, and low extracurricular involvement. Model 2 also detected a direct effect of agency-reported childhood maltreatment on the adult outcome. Regardless of the type of maltreatment or data source used, school factors mediated the associations of childhood maltreatment on adult educational attainment. Promoting school engagement and reducing disciplinary referrals for maltreated youth could improve their educational attainment over the long term.

Positive and Negative Peer Influence in Residential Care.

The potential for negative peer influence has been well established in research, and there is a growing interest in how positive peer influence also impacts youth. No research, however, has concurrently examined positive and negative peer influence in the context of residential care. Clinical records for 886 residential care youth were used in a Hierarchical Linear Model analysis to examine the impact of negative and positive peer influence on naturally occurring patterns of serious problem behavior over time. Negative peer influence, where the majority of youth in a home manifested above the average number of serious behavior problems, occurred 13.7% of the time. Positive peer influence, where the majority of youth manifested no serious problem behaviors for the month, occurred 47.7% of the time. Overall, youth problem behavior improved over time. There were significantly lower rates of serious problem behavior in target youth during positive peer influence months. Conversely, there were significantly higher rates of serious problem behaviors in target youth during negative peer influence months. Negative peer influence had a relatively greater impact on target peers' serious behavior problems than did positive peer influence. Caregiver experience significantly reduced the impact of negative peer influence, but did not significantly augment positive peer influence. Months where negative peer influence was combined with inexperienced caregivers produced the highest rates of serious problem behavior. Our results support the view that residential programs for troubled youth need to create circumstances that promote positive and control for negative peer influence.

Developmental effects of childhood household adversity, transitions, and relationship quality on adult outcomes of socioeconomic status: Effects of substantiated child maltreatment.

The degree to which child maltreatment interacts with other household adversities to exacerbate risk for poor adult socioeconomic outcomes is uncertain. Moreover, the effects of residential, school, and caregiver transitions during childhood on adult outcomes are not well understood. This study examined the relation between household adversity and transitions in childhood with adult income problems, education, and unemployment in individuals with or without a childhood maltreatment history. The potential protective role of positive relationship quality in buffering these risk relationships was also tested. Data were from the Lehigh Longitudinal Study (n = 457), where subjects were assessed at preschool, elementary, adolescent, and adult ages. Multiple group path analysis tested the relationships between childhood household adversity; residential, school, and caregiver transitions; and adult socioeconomic outcomes for each group. Caregiver relationship quality was included as a moderator, and gender as a covariate. Household adversity was negatively associated with education level and positively associated with income problems for non-maltreated children only. For both groups, residential transitions was negatively associated with education level and caregiver transitions was positively associated with unemployment problems. Relationship quality was positively associated with education level only for non-maltreated children. For children who did not experience maltreatment, reducing exposure to household adversity is an important goal for prevention. Reducing exposure to child maltreatment for all children remains an important public health priority. Results underscore the need for programs and policies that promote stable relationships and environments.

Photophysics of Zinc Porphyrin Aggregates in Dilute Water-Ethanol Solutions.

Dimeric and multimeric aggregates of a model metalloporphyrin, zinc tetraphenylporphyrin (ZnTPP), have been produced in a controlled manner by incrementally increasing the water content of dilute aqueous ethanol solutions. Steady state absorption, fluorescence emission, and fluorescence excitation spectra have been measured to identify the aggregates present as a function of solvent composition. The dynamics of the excited states of the aggregates produced initially by excitation in the Soret region have been measured by ultrafast fluorescence upconversion techniques. Only the monomer produces measurable emission from S2 with a picosecond lifetime; all Soret-excited aggregates, including the dimer, decay radiationlessly on a femtosecond time scale. The S1 state is the only significant product of the radiationless decay of the S2 state of the excited monomer, and the aggregates also produce substantial quantum yields of S1 fluorescence when initially excited in the Soret region. The resulting fluorescent aggregates all decay on a subnanosecond time scale, likely by a mechanism that involves dissociation of the excited monomer from the excitonic multimer. The ZnTPP dimers excited at their ground state geometries in the Soret region exhibit a dynamic behavior that is quite different from those produced following noncoherent triplet-triplet annihilation under the same conditions. The important implications of these observations in determining the aggregation conditions promoting efficient photon upconversion by excitonic annihilation in a variety of media are thoroughly discussed.

Psychometric Evaluation of the Symptoms and Functioning Severity Scale (SFSS) Short Forms with Out-of-Home Care Youth.

BACKGROUND: There is a need for brief progress monitoring measures of behavioral and emotional symptoms for youth in out-of-home care. The Symptoms and Functioning Severity Scale (SFSS; Bickman et al., 2010) is one measure that has clinician and youth short forms (SFSS-SFs); however, the psychometric soundness of the SFSS-SFs with youth in out-of-home care has yet to be examined. OBJECTIVE: The objective was to determine if the psychometric characteristics of the clinician and youth SFSS-SFs are viable for use in out-of-home care programs. METHODS: The participants included 143 youth receiving residential treatment and 52 direct care residential staff. The current study assessed internal consistency and alternate forms reliability for SFSS-SFs for youth in a residential care setting. Further, a binary classification test was completed to determine if the SFSS-SFs similarly classified youth as the SFSS full version for low- and elevated-severity. RESULTS: The internal consistency for the clinician and youth SFSS-SFs was adequate (α = .75 to .82) as was the parallel forms reliability (r = .85 to .97). The sensitivity (0.80 to 0.95), specificity (0.88 to 0.97), and overall accuracy (0.89 to 0.93) for differentiating low and elevated symptom severity was acceptable. CONCLUSIONS: The clinician and youth SFSS-SFs have acceptable psychometrics and may be beneficial for progress monitoring and additional research should clarify their potential for progress monitoring of youth in out-of-home programs.

Two-Dimensional Electronic Spectroscopy of Light-Harvesting Complex II at Ambient Temperature: A Joint Experimental and Theoretical Study.

We have performed broad-band two-dimensional (2D) electronic spectroscopy of light-harvesting complex II (LHCII) at ambient temperature. We found that electronic dephasing occurs within ∼60 fs and inhomogeneous broadening is approximately 120 cm(-1). A three-dimensional global fit analysis allows us to identify several time scales in the dynamics of the 2D spectra ranging from 100 fs to ∼10 ps and to uncover the energy-transfer pathways in LHCII. In particular, the energy transfer between the chlorophyll b and chlorophyll a pools occurs within ∼1.1 ps. Retrieved 2D decay-associated spectra also uncover the spectral positions of corresponding diagonal peaks in the 2D spectra. Residuals in the decay traces exhibit periodic modulations with different oscillation periods. However, only one of them can be associated with the excitonic cross-peaks in the 2D spectrum, while the remaining ones are presumably of vibrational origin. For the interpretation of the spectroscopic data, we have applied a refined exciton model for LHCII. It reproduces the linear absorption, circular dichroism, and 2D spectra at different waiting times. Several components of the energy transport are revealed from theoretical simulations that agree well with the experimental observations.

Side chains control dynamics and self-sorting in fluorescent organic nanoparticles.

To develop fluorescent organic nanoparticles with tailored properties for imaging and sensing, full control over the size, fluorescence, stability, dynamics, and supramolecular organization of these particles is crucial. We have designed, synthesized, and fully characterized 12 nonionic fluorene co-oligomers that formed self-assembled fluorescent nanoparticles in water. In these series of molecules, the ratio of hydrophilic ethylene glycol and hydrophobic alkyl side chains was systematically altered to investigate its role on the above-mentioned properties. The nanoparticles consisting of π-conjugated oligomers containing polar ethylene glycol side chains were less stable and larger in size, while nanoparticles self-assembled from oligomers containing nonpolar pendant chains were more stable, smaller, and generally had a higher fluorescence quantum yield. Furthermore, the dynamics of the molecules between the nanoparticles was enhanced if the number of hydrophilic side chains increased. Energy transfer studies between naphthalene and benzothiadiazole fluorene co-oligomers with the same side chains showed no exchange of molecules between the particles for the apolar molecules. For the more polar systems, the exchange of molecules between nanoparticles took place at room temperature or after annealing. Self-assembled nanoparticles consisting of π-conjugated oligomers having different side chains caused self-sorting, resulting either in the formation of domains within particles or the formation of separate nanoparticles. Our results show that we can control the stability, fluorescence, dynamics, and self-sorting properties of the nanoparticles by simply changing the nature of the side chains of the π-conjugated oligomers. These findings are not only important for the field of self-assembled nanoparticles but also for the construction of well-defined multicomponent supramolecular materials in general.

Morphology-dependent energy transfer dynamics in fluorene-based amphiphile nanoparticles.

Nanoparticles are interesting systems to study because of their large range of potential uses in biological imaging and sensing. We investigated molecular nanoparticles formed by fast injection of a small volume of molecularly dissolved fluorene-derivative amphiphilic molecules into a polar solvent, which resulted in solid spherical particles of ∼80 nm diameter with high stability. Energy transfer studies were carried out on two-component nanoparticles that contained mixtures of donor and acceptor amphiphiles of various fractions. We conducted time-resolved photoluminescence measurements on the two-component nanoparticles in order to determine whether the fundamental donor-acceptor interaction parameter (the Förster radius) depends on the acceptor concentration. The Förster radius was found to be large for very low incorporated acceptor fractions (<0.1%), but it declined with increasing concentration. These changes were concomitant with shifts in the acceptor emission and absorption circular dichroism spectra that indicated an increasing clustering of acceptors into domains as their fraction was raised. In addition, for acceptor fractions below 2% the extracted Förster radii were found to be significantly larger than predicted from donor-acceptor spectral overlap calculations, in accordance with efficient excitation diffusion within the donor matrix, aiding the overall transfer to acceptors. We conclude that energy transfer in two-component nanoparticles shows a complex interplay between phase segregation of the constituent donor and acceptor molecules and excitation diffusion within their domains.