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Strain has a unique and sometimes unpredictable impact on the properties and reactivity of molecules. To thoroughly describe strain in molecules, a computational tool that relates strain energy to reactivity by localizing and quantifying strain was developed. Strain energy is calculated local to every coordinate in the molecule and areas of higher strain are shown experimentally to be more reactive. Not only does this tool directly compare strain energy in parts of the same molecule, but it also computes total strain to give a full picture of molecular strain energy. It is freely available to the public on GitHub under the name StrainViz and much of the workflow is automated to simplify use for non-experts. Unique insight into the reactivity of curved aromatic molecules and strained alkyne bioorthogonal reagents is described within. 

Cycloparaphenylenes have promise as novel fluorescent materials. However, shifting their fluorescence beyond 510 nm is difficult. Herein, we computationally explore the effect of incorporating electron accepting and electron donating units on CPP photophysical properties at the CAM-B3LYP/6-311G** level. We demonstrate that incorporation of donor and acceptor units may shift the CPP fluorescence as far as 1193 nm. This computational work directs the synthesis of bright red-emitting CPPs. Furthermore, the nanohoop architecture allows for interrogation of strain effects on common conjugated polymer donor and acceptor units. Strain results in a bathochromic shift versus linear variants, demonstrating the value of using strain to push the limits of low band gap materials. 

[ n ]Cycloparaphenylenes, or “carbon nanohoops,” are unique conjugated macrocycles with radially oriented π-systems similar to those in carbon nanotubes. The centrosymmetric nature and conformational rigidity of these molecules lead to unusual size-dependent photophysical characteristics. To investigate these effects further and expand the family of possible structures, a new class of related carbon nanohoops with broken symmetry is disclosed. In these structures, referred to as meta [ n ]cycloparaphenylenes, a single carbon–carbon bond is shifted by one position in order to break the centrosymmetric nature of the parent [ n ]cycloparaphenylenes. Advantageously, the symmetry breaking leads to bright emission in the smaller nanohoops, which are typically non-fluorescent due to optical selection rules. Moreover, this simple structural manipulation retains one of the most unique features of the nanohoop structures—size dependent emissive properties with relatively large extinction coefficients and quantum yields. Inspired by earlier theoretical work by Tretiak and co-workers, this joint synthetic, photophysical, and theoretical study provides further design principles to manipulate the optical properties of this growing class of molecules with radially oriented π-systems.