Herein, we present a strategy to enable a maintained emissive behavior in the self‐assembled state by enforcing an anti‐cooperative self‐assembly involving weak intermolecular dye interactions. To achieve this goal, we designed a conformationally flexible monomer unit 1 with a central 1,3‐substituted (diphenyl)urea hydrogen bonding synthon that is tethered to two BODIPY dyes featuring sterically bulky trialkoxybenzene substituents at the meso‐position. The competition between attractive forces (H‐bonding and aromatic interactions) and destabilizing effects (steric and competing conformational effects) limits the assembly, halting the supramolecular growth at the stage of small oligomers. Given the presence of weak dye–dye interactions, the emission properties of molecularly dissolved 1 are negligibly affected upon aggregation. Our findings contribute to broadening the scope of emissive supramolecular assemblies and controlled supramolecular polymerization.
We
investigate the effect of assembly on charge transfer, charge
recombination, and the persistence of radical cations in halogen-substituted
triphenylamine (TPA) dimers. A series of urea-tethered TPA derivatives 1 (X = H, Cl, Br, and I) are compared, which have one phenyl
group modified at the para position with a halogen.
Ureas direct the assembly of these derivatives while halogen substituents
influence the packing of the TPA units. These modifications affect
the generation and persistence of TPA radical cations as monitored
by electron paramagnetic resonance (EPR) spectroscopy. The formation
and degradation pathways of the radical cations in solution and gas
phase were probed by ion-mobility spectrometry mass spectrometry.
In contrast, supramolecular assembly enhanced the stability of these
materials as well as the persistence of their photogenerated radical
cations, which appear to undergo charge recombination without degradation.
Greater quantities of these radical cations are observed for the bromo
and non-halogenated derivatives (1Br, 1H). Time-dependent density functional theory (TD-DFT) calculations
on single molecules and hydrogen-bonded dimers suggest the stability
of TPA radical cations largely depends on initial photoinduced charge
separation and electronic coupling between assembled TPA dimers. The
latter was found to be about 7 times stronger in 1I than
in 1Br dimers, which may explain faster charge recombination
and shorter lifetimes of 1I radicals. Transient absorption
(TA) spectroscopy and TD-DFT were able to identify the charged species
for 1Br along with the kinetic traces and measured lifetime
of ∼80 ns. Fluorescence quenching studies are consistent with
initial charge separation and subsequent charge transfer event between
nearby TPAs. Future exploration will focus on the mobility and application
of these TPA assemblies as hole transport materials.
Drought stress provokes plants to change their growth pattern and biochemical contents to overcome adverse situations. Soybean was grown under 40 (drought) and 80% (control) of field capacity (FC) to determine the morpho-physiological and biochemical alterations that occur under drought conditions. The experiment was conducted following a randomized complete block design with three replications. The results showed that drought exerted detrimental effects on photosynthetic attributes, leaf production, pigment and water content, plant growth, and dry matter production of soybean. However, drought favored producing a higher amount of proline and malondialdehyde in soybean leaf than in the control. The pod and seed production, grain size, and seed yield of soybean were also adversely affected by the drought, where genotypic variations were conspicuous. Interestingly, the studied morpho-physiological and biochemical parameters of AGS383 were minimally affected by drought. This genotype was capable of maintaining healthier root and shoot growth, greater leaf area, preserving leaf greenness and cell membrane stability, higher photosynthesis, absorbing water and sustaining leaf water potential, and lower amount of proline and malondialdehyde production under drought conditions. The heavier grains of AGS383 make it out yielder under both growth conditions. Considering the changes in morpho-physiological, biochemical, and yield contributing parameters, the genotype AGS383 could be cultivated as a relatively drought-tolerant, high-yielding soybean variety. Further study is needed to uncover the genes responsible for the adaptation of AGS383 to drought-stress environments, and this genotype might be used as parent material in a breeding program to develop a high-yielding, drought-tolerant soybean variety.
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