Ultrafast Energy Transfer Process in Doped-Anthracene Nanoaggregates is Controlled by Exciton Diffusion: Multiple Doping Leads to Efficient White Light Emission

Abstract

Quite similar structures of polycyclic aromatic hydrocarbons make them suitable for doping of one molecule into the crystalline structure or aggregate of another and tuning of the optical properties of the composite system. Anthracene nanoaggregates, singly or multiply doped with perylene, tetracene, and pentacene, have been synthesized using reprecipitation technique. Following photoexcitation of anthracene molecule in the nanoaggregate, anthracene exciton transfers energy to the dopant molecule(s). Energy transfer (ET) efficiency of about 98% could be achieved with the concentration of about 6 × 10 −3 mol dm −3 for perylene or tetracene as the acceptor and about 92% efficiency with the doping concentration of about 5 × 10 −2 mol dm −3 for pentacene as the acceptor. Very fast energy transfer rates (∼3−6 × 10 11 dm 3 mol −1 s −1 ) observed here could not be explained by invoking Forster's energy transfer mechanism. However, the rate of diffusion of anthracene exciton determined experimentally using exciton−exciton annihilation reaction in the anthracene nanoaggregate matrix has been shown to agree well with the ET rate. This observation leads us to conclude that the ET rate in the nanoaggregate matrix is controlled by exciton diffusion. Using those three dopants with proper concentration ratios, efficient white light emission has been achieved following optical excitation of the nanoaggregate sample at the absorption band of the anthracene molecule.

Organizing Crystalline Functionalized Pentacene Using Periodicity of Poly(Vinyl Alcohol)

“…However, it was also observed that reprecipitation of TIPS-Pn into dilute aqueous poly­(vinyl alcohol) (PVA) solutions induced an identical effect, and an additional study has since reported modulation of pyrene NP morphology using a similar method . PVA is a common additive in the preparation of both organic − ,− and inorganic − NP dispersions, although the rationale for its use is often unclear. Some authors have noted that inclusion of PVA appears to stabilize NP dispersions through binding to the surface and acting as a capping agent, , while others have also suggested that it influences the nucleation stage through controlling factors such as viscosity and surface tension .…”

“…PVA is commonly used as a templating or emulsifying agent in the preparation of organic NP dispersions, typically acting as a capping agent to promote particle dispersity and minimize aggregation. ,,,,, Previous studies have shown that inclusion of PVA in the reprecipitation step slows the growth of perylene NPs and favors the formation of the crystalline phase in pyrene NPs . However, in all of these previous reports, PVA acts as a template to guide the formation of NPs to a desired size or morphology and is considered only within the context of NP formation and growth.…”

Ultrafast Dynamics and Estimation of Singlet Exciton Diffusion Parameters for Nanoaggregates of peri and bay Anisyl Perylene

“…The observed decays were analyzed with a suitable exponential function to obtain the best fits for the decays. Sub-ps time-resolved emission and transient absorption experiments were executed by using fluorescence up-conversion (FOG-100, CDP corporation, Russia) and ultrafast transient absorption (ExciPRO, CDP Corporation, Russia) spectrometers, respectively. , The above spectroscopic setups are coupled with an amplified ultrafast laser module obtained from Amplitude Technologies, France. The detailed elaboration of the above experimental setups are available in previous reports.…”

“…67 The values for R a are 0.9 ± 0.21 and 1.49 ± 0.28 nm for peri and bay derivatives, respectively. Further, the values of the exciton diffusion coefficient and singlet exciton lifetime are used to estimate the exciton diffusion length (L D = √6Dτ), 70 which is nothing but the mean distance travelled by an exciton during its lifetime. These parameters are provided in Table 2 for both the compounds.…”

Disproportionation-induced solid-state fluorescence in 6,13-dihydropentacenes

“…The decaying emission of the naphthaleneimide skeleton may be explained in terms of an energy transfer from 3a to 4a. 11 Fig. S6 † shows the concentration-dependent emission spectra of 3a in CHCl 3 .…”