Exciton interactions in molecular aggregates play ac rucial role in tailoring the optical behaviour of p-conjugated materials.Though vital for optoelectronic applications,i deal Greek cross-dipole (a = 908 8)s tacking of chromophores remains elusive. We report an ovel Greek cross (+ +)a ssembly of 1,7dibromoperylene-3,4,9,10-tetracarboxylic tetrabutylester (PTE-Br 2 )which exhibits null exciton coupling mediated monomer-like optical characteristics in the crystalline state.Incontrast, nonzero exciton coupling in X-type (a = 70.28 8,P TE-Br 0 )a nd J-type (a = 08 8, q = 48.48 8,P TE-Br 4 )a ssemblies have perturbed optical properties.Additionally,the semi-classical Marcus theory of charge-transfer rates predicts aselective hole transport phenomenon in the orthogonally stacked PTE-Br 2 .P recise rotation angle dependent optoelectronic properties in crystalline PTE-Br 2 can have consequences in the rational design of novel p-conjugated materials for photonic and molecular electronic applications. Conflict of interestTheauthors declare no conflict of interest. Figure 3. a) Computed anisotropic mobility along the ac plane and b) schematic depiction of the charge-filtering (selective hole transfer (k h )) phenomenon in PTE-Br 2 Greek cross (+ +)a ggregate.

Quantum theory of atoms-in-molecules and Hirshfeld surface analyses indicated an increase in the extent of (i) C-H···H-C; (ii) C-H···O, (iii) π-π interactions and a decrease in the extent of (i) σ-π interaction, (ii) an interplanar angle between the vicinal pyrene units in a series of acetylpyrene derivatives offering blue-green-orange emissive crystals.

Efficient photoinduced charge separation in artificial multichromophoric architectures relies on two critical factors, (i) electronic coupling and (ii) solvation. While the coherent exciton interactions delocalize the excitation energy among molecules, the solvation-dependent dynamical disorder tends to localize it. Local environments such as solvent polarity/dielectric environments exhibit profound effect on mediating the excited-state relaxation dynamics via specific electronic/geometric changes in chromophore multimers. Herein, a comprehensive account of the solvent governed distinct exciton coupling and symmetry breaking charge separation in a near-orthogonal perylenimide dimer (PP) is presented employing steady-state, femtosecond transient absorption measurements and quantum chemical calculations. Steady-state absorption measurements of the PP dimer reveal apparent electronic coupling between the two monomeric units, wherein the fluorescence measurements reveal a strong fluorescence character in nonpolar solvent, but a significantly quenched state is observed in polar solvent. Ultrafast transient absorption measurements reveal that the fluorescence quenching in polar solvent arises from a photoinduced symmetry-breaking charge transfer (SBCT) process and a subsequent population of the charge-separated radical ion-pair state. Contrastingly, in nonpolar solvent, the charge transfer is endothermic and energetically not feasible. Manifestly, the dimer in nonpolar solvent undergoes a conformational planarization within 20 ps accompanied by excitation delocalization over the two identical monomers in the lowest excited singlet state as evident from the dominant stimulated emission (around 580 nm) and the excited-state absorption (around 740 nm) in the femtosecond transient absorption spectra. Observed solvent-mediated selective control on the excited-state relaxation pathways in the near-orthogonal PP dimer can help shed light on the mechanisms of energy/charge transfer in molecular systems and guide the design of novel high-performance photovoltaic materials.

The fluorescent probe 2-aminopurine (2Ap) has been used for decades to study local conformational fluctuations in DNA. Steady-state and time-resolved measurements of 2Ap fluorescence have been used to predict specific conformational states through suitable modeling of the quenching of the fluorescence of a 2Ap residue incorporated site-specifically into a DNA strand. The success of this approach has been limited by a lack of understanding of the precise factors responsible for the complex, multiexponential decays observed experimentally. In this study, dinucleotides composed of 2Ap and adenine were studied by the time-correlated single-photon counting technique to investigate the causes of heterogeneous emission kinetics. Contrary to previous reports, we argue that emission from 2Ap that is stacked with a neighboring base contributes negligibly to the emission signals recorded more than 50 ps after excitation, which are instead dominated by emission from unstacked 2Ap. We find that the decay kinetics can be modeled using a continuous lifetime distribution, which arises from the inherent distance dependence of electron transfer rates without the need to postulate a small number of discrete states with decay times derived from multiexponential fits. These results offer a new perspective on the quenching of 2Ap fluorescence and expand the information that can be obtained from experiments.

Twisted donor-on-donor and acceptor-on-acceptor bicontinuous assembly in all-carbon pyren-1-ylaceanthrylene (PA) dyad extends the survival time of the photoinduced radical ion-pair intermediates. Aceanthrylene, a functional analog of C, acts as a versatile electron acceptor owing to its high electron affinity and visible light absorption. Antithetical trajectories of the excitons in the nonparallel π-ways led to persistent radical ion-pair intermediates in aggregated (τ ∼ 1.28 ns) vs monomeric (τ ≤ 110 fs) PA dyad as observed using femtosecond transient absorption spectroscopy. Marcus theory of charge transfer rates predicts an ambipolar transport characteristic in crystalline PA, thereby endorsing PA as an all-carbon DA hybrid for nonfullerene photovoltaic applications.