Interactions between nonfullerene acceptors lead to unstable ternary organic photovoltaic cells.

For organic photovoltaic (OPV) devices to achieve consistent performance and long operational lifetimes, organic semiconductors must be processed with precise control over their purity, composition, and structure. This is particularly important for high volume solar cell manufacturing where control of materials quality has a direct impact on yield and cost. Ternary-blend OPVs containing two acceptor-donor-acceptor (A-D-A)-type nonfullerene acceptors (NFAs) and a donor have proven to be an effective strategy to improve solar spectral coverage and reduce energy losses beyond that of binary-blend OPVs.

Chemoselective Photoreaction of Enamides: Divergent Reactivity towards [3+2]-Photocycloaddition vs Paternò-Büchi Reaction.

Photoreaction of enamides tethered to a phenyl ketone leads to either [3+2]-photocycloaddition or Paternò-Büchi reaction. This divergence in chemical reactivity originating from the same excited state was dependent on the reaction temperature. At low temperatures the Paternò-Büchi reaction was preferred, whereas at higher temperatures there was preference toward formation of [3+2]-photoproduct.

Uncovering New Excited State Photochemical Reactivity by Altering the Course of the De Mayo Reaction.

An unprecedented and previously unknown photochemical reactivity of 1,3-dicarbonyl compounds is observed with amino-alkenes leading to dihydropyrans. This novel photochemical reactivity changes the established paradigm related to the De Mayo reaction between 1,3-dicarbonyl compounds and alkenes. This new reaction allows convenient access to the Marmycin core in a single step from commercially available reactants.

Taming the excited state reactivity of imines - from non-radiative decay to aza Paternò-Büchi reaction.

This review highlights the excited state characteristics of imines and processes that govern their photochemical and photophysical properties. This review examines the pathways for deactivation and types of photochemical reactions that originate from excited imines. This review also features recent strategies that are developed to circumvent the fundamental issues that have plagued the development of the aza Paternò-Büchi reaction.

Realizing an Aza Paternò-Büchi Reaction.

Intramolecular atropselective aza Paternò-Büchi reaction involving atropisomeric enamide and imine functionalities under sensitized irradiation leads to azetidine products in good yield and selectivity (ee >96 %). A mechanistic model based on detailed photophysical and isomerization kinetic studies is provided that shed light into the reactivity of enamides leading to aza Paternò-Büchi reaction.

Tale of Twisted Molecules. Atropselective Photoreactions: Taming Light Induced Asymmetric Transformations through Non-biaryl Atropisomers.

Photochemical transformations are a powerful tool in organic synthesis to access structurally complex and diverse synthetic building blocks. However, this great potential remains untapped in the mainstream synthetic community due to the challenges associated with stereocontrol originating from excited state(s). The finite lifetime of an excited state and nearly barrierless subsequent processes present significant challenges in manipulating the stereochemical outcome of a photochemical reaction.

Transposed Paternò-Büchi Reaction.

A complementary strategy of utilizing ππ* excited state of alkene instead of nπ* excited state of the carbonyl chromophore in a "transposed Paternò-Büchi" reaction is evaluated with atropisomeric enamides as the model system. Based on photophysical investigations, the nature of excited states and the reactive pathway was deciphered leading to atropselective reaction. This new concept of switching of excited-state configuration should pave the way to control the stereochemical course of photoreaction due to the orbital approaches required for photochemical reactivity.

Ferroelectric Polymer Matrix for Probing Molecular Organization in Perylene Diimides.

Ferroelectric films of poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) provide a controlled environment to study the aggregation tendency of functional molecules such as perylene diimides (PDIs). The local electric field and free volume confinement parameters offered by the matrix are tailored to study the organizational and assembly characteritics of molecular acceptors. The optical properties of planar and nonplanar PDIs in the ferroelectric polymer matrix were studied systematically over a wide range that encompassed the ferroelectric transition temperature.

Nonplanar Perylene Diimides as Potential Alternatives to Fullerenes in Organic Solar Cells.

Perylene diimides (PDIs) are attractive alternatives to fullerenes as electron transporters because of their optoelectronic properties, durability, and ease of synthesis. Belying this promise, devices that utilize PDIs as electron acceptors have low efficiencies. The primary deficiency in such cells is the low short circuit current density (JSC), which is traceable to the crystallinity of PDIs.