Reduced Intrinsic Non-Radiative Losses Allow Room-Temperature Triplet Emission from Purely Organic Emitters.

Persistent luminescence from triplet excitons in organic molecules is rare, as fast non-radiative deactivation typically dominates over radiative transitions. This work demonstrates that the substitution of a hydrogen atom in a derivative of phenanthroimidazole with an N-phenyl ring can substantially stabilize the excited state. This stabilization converts an organic material without phosphorescence emission into a molecular system exhibiting efficient and ultralong afterglow phosphorescence at room temperature.

Effect of H- and J-Aggregation on the Photophysical and Voltage Loss of Boron Dipyrromethene Small Molecules in Vacuum-Deposited Organic Solar Cells.

An understanding of the factors limiting the open-circuit voltage ( V) and related photon energy loss mechanisms is critical to increase the power conversion efficiency (PCE) of small-molecule organic solar cells (OSCs), especially those with near-infrared (NIR) absorbers. In this work, two NIR boron dipyrromethene (BODIPY) molecules are characterized for application in planar (PHJ) and bulk (BHJ) heterojunction OSCs. When two H atoms are substituted by F atoms on the peripheral phenyl rings of the molecules, the molecular aggregation type in the thin film changes from the H-type to J-type.

Hole Transport in Low-Donor-Content Organic Solar Cells.

Organic solar cells with an electron donor diluted in a fullerene matrix have a reduced density of donor-fullerene contacts, resulting in decreased free-carrier recombination and increased open-circuit voltages. However, the low donor concentration prevents the formation of percolation pathways for holes. Notwithstanding, high (>75%) external quantum efficiencies can be reached, suggesting an effective hole-transport mechanism.

Small Molecule Near-Infrared Boron Dipyrromethene Donors for Organic Tandem Solar Cells.

Three furan fused boron dipyrromethenes (BODIPYs) with a CF group on the meso-carbon are synthesized as near-infrared absorbing materials for vacuum processable organic solar cells. The best single junction device reaches a short-circuit current (j) of 13.3 mA cm and a power conversion efficiency (PCE) of 6.

Organic narrowband near-infrared photodetectors based on intermolecular charge-transfer absorption.

Blending organic electron donors and acceptors yields intermolecular charge-transfer states with additional optical transitions below their optical gaps. In organic photovoltaic devices, such states play a crucial role and limit the operating voltage. Due to its extremely weak nature, direct intermolecular charge-transfer absorption often remains undetected and unused for photocurrent generation.

Aza-BODIPY Derivatives Containing BF(CN) and B(CN) Moieties.

Two novel aza-BODIPY derivatives are synthesized, with the fluorine atoms in the BF moiety replaced by cyano groups. The introduction of cyano groups changes the phenyl substituents on the 3,5 positions from parallel to antiparallel. The HOMO/LUMO energy levels are stabilized gradually upon increasing the number of cyano groups, and the photophysical properties show corresponding shifts.

Absorption Tails of Donor:C Blends Provide Insight into Thermally Activated Charge-Transfer Processes and Polaron Relaxation.

In disordered organic semiconductors, the transfer of a rather localized charge carrier from one site to another triggers a deformation of the molecular structure quantified by the intramolecular relaxation energy. A similar structural relaxation occurs upon population of intermolecular charge-transfer (CT) states formed at organic electron donor (D)-acceptor (A) interfaces. Weak CT absorption bands for D-A complexes occur at photon energies below the optical gaps of both the donors and the C acceptor as a result of optical transitions from the neutral ground state to the ionic CT state.

EPR analysis and DFT computations of a series of polynitroxides.

Polynitroxides with varying numbers of nitroxide groups (one to four) derived from different aromatic core structures show intramolecular electron spin-spin coupling. The scope of this study is to establish an easy methodology for extracting structural, dynamical, and thermodynamical information from the EPR spectra of these polynitroxides which might find use as spin probes in complex systems, such as biological and host/guest systems, and as polarizing agents in dynamic nuclear polarization (DNP) applications. Density functional theory (DFT) calculations at the B3LYP/6-31G(d) level provided information on the structural details such as bond lengths and angles in the gas phase, which were compared with the single crystal X-ray diffraction data in the solid state.

Synthesis of polynitroxides based on nucleophilic aromatic substitution.

The scope and limitations of the synthesis of polynitroxides by nucleophilic substitution of electron-deficient fluorinated aromatic compounds are described. The method provides a facile route to the formation of polynitroxides exhibiting strong electron exchange between nitroxide groups.

Thiophene-thiophene versus phenyl-phenyl coupling in 2-(Diphenylamino)-Thiophenes: an ESR-UV/Vis/NIR spectroelectrochemical study.

The oxidation of several 2-diphenylamino-substituted thiophenes and N,N'-bis(2-diphenylamino-5-thienyl)-substituted phenylene-1,4-diamines with different substitution patterns in the 5-position of their thiophene moieties was studied by cyclovoltammetric and spectroelectrochemical measurements (ESR, UV/Vis/NIR). These measurements revealed both the structure of the oxidation products obtained and that of their cationic intermediates, as well as the pathway of their formation and follow-up reactions. Thus, the formation of the radical cations in the first electrochemical oxidation step of the target molecules was demonstrated.