Search

Multiple ultrafast spectroscopic techniques and quantum chemical simulations (QCS) were used to investigate the excited state dynamics of BCC-TPTA. This organic chromophore is believed to possess excited state dynamics governed by a thermally activated delayed fluorescence (TADF) mechanism with a reported internal quantum efficiency (ηIQE) of 84%. In addition, a significant enhancement in its quantum yield (Φ) in solution after purging oxygen has been reported. This Φ enhancement has been widely accepted as due to a delayed fluorescence process occurring on the μs time-scale. The spectroscopic measurements were carried out both in solution and blended films, and from fs to μs time-scales. The excited state dynamics of Rhodamine B and Ir(BT)2(acac) were also probed for comparison. Investigations in the absence of oxygen were also carried out. Our time-correlated single photon counting (TCSPC) measurements revealed a lack of a long-lived emissive lifetime for BCC-TPTA in any of the media tested. Our ns transient absorption spectroscopy (ns TAS) experiments revealed that BCC-TPTA does not possess triplet transient states that could be linked to a delayed fluorescence process. Instead, the evidence obtained from our spectroscopic tools suggests that BCC-TPTA has the excited state dynamics of a typical fluorescence chromophore and that just comparing the Φ difference before and after purging oxygen from the solution is not an accurate method to claim excited state dynamics governed by a delayed fluorescence mechanism. Consequently, we believe that previous studies, in which the photo-physics of organic chromophores with TADF characteristics are reported, may have overlooked the influence of the host materials on the obtained optical properties in blended films.

We developed a new optical method to determine the rate of reverse intersystem crossing (krISC) in thermally activated delayed fluorescent (TADF) organic chromophores using time-resolved transient ...

A new series of donor–acceptor ladder-type molecules were synthesized via Scholl reaction. These molecules contain up to 25-fused rings but still show good air stability and good solubility. The ring-fusing reaction is found to be sensitive to the nature of the side-chain in donor units. The molecular conformations were investigated by 2D NMR and DFT calculations. The photophysical properties were investigated and an intense intramolecular charge-transfer was observed. All of the molecules exhibit two-photon absorption (TPA) activity, and their TPA cross-section shows a linear relationship with increasing conjugation length of the thienoacene-PDI derivatives.

We investigate the influence of the heteroatom on the electronic and photophysical properties of four conjugated polymers based on 3,7-didodecyl-2,6-di(thiophen-2-yl)benzo[1,2-b:4,5-b′]difuran (BDF) as the donor and 3,6-di(thiophen-2-yl)-1,4-diketopyrrolo[3,4-c]pyrrole (TDPP) or 3,6-di(2-furanyl)-1,4-diketopyrrolo[3,4-c]pyrrole (FDPP) as the acceptor. The polymers with a furan as the linker showed higher extinction coefficients than their thiophene counterparts. Ultrafast fluorescence decay showed that the exciton relaxation process is affected by the type of linker in these conjugated polymers. Theoretical calculations showed that the polymers with a furan as the linker are more planar than their thiophene analogues. Also, theoretical calculation showed that the polymers with a thiophene as the linker have larger transition dipole moments. The two-photon absorption cross sections (TPACS) of the polymers with a furan as the linker were larger than their thiophene polymer analogues. These results suggest t...

A simulation-led strategy enacts two-electron transfer between an intramolecular singlet fission chromophore (tetracyanomethylene quinoidal bithiopehene with β,β′-solubilizing groups) and multielectron acceptor (anthraquinone). The thermodynamic plausibility of multielectron transfer from a double-triplet state and the absorption spectra of electron transfer (ET) products were predicted using quantum chemical simulations. These predictions are consistent with experimental observations of reduced lifetimes in time-resolved fluorescence spectroscopy, changes in transmission profile, and appearance of new absorption bands in transient absorption spectroscopy, all of which support multi-ET in the QOT2/AQ mixture. The analysis suggests 2ET is favored over 1ET by a 2.5:1 ratio.

Decapitating phorid flies in the genus Pseudacteon are being studied as classical biological control agents of the red imported fire ant, Solenopsis invicta Buren (Hymenoptera: Formicidae). Pseudacteon curvatus Borgmeier (Diptera: Phoridae) is a small decapitating fly that attacks small fire ant workers. We released a biotype of P. curvatus from Formosa, Argentina, at three sites near Gainesville, FL. Field releases were conducted in the spring and summer of 2003 and monitored monthly. Flies were discovered within 5 weeks at the spring site and then monthly thereafter. By late spring 2004, flies released at this site had expanded 1.6 km both north and south and about 0.8 km westward. Initially, we found no flies from the two summer 2003 releases but we were successful at finding them 8 months after release during spring 2004. This paper documents the first successful release(s) of P. curvatus on red imported fire ants in the United States.

We tested the host specificity of Pseudacteon curvatus Borgmeier from Formosa, Argentina, on North American colonies of the red imported fire ant, Solenopsis invicta Buren, and the native fire ants Solenopsis geminata (F.) and Solenopsis xyloni McCook. No-choice tests showed that P. curvatus hovered over and attacked all three species of fire ants. The number of pupae successfully completing development to adult flies in the trials was 5.03 ± 1.55 (mean ± SE) per female fly in S. invicta, 0.66 ± 0.24 per female fly in S. xyloni, and 0 per female fly in S. geminata. Paired preference tests showed that P. curvatus preferred to hover over S. invicta instead of S. xyloni 77 ± 3% (mean ± SE) of the time and preferred S. invicta over S. geminata 87 ± 4% of the time. The oviposition attempts of active female P. curvatus were 2.8 times higher on S. invicta than on S. xyloni and 16 times higher on S. invicta than on S. geminata. These results demonstrate that this new biotype of P. curvatus is more host specific to North American red imported fire ants than a previous biotype collected from black imported fire ants.