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Aryl‐maleimides undergo a novel [2+4]‐photodimerization instead of the expected [2+2]‐photodimerization under both direct irradiation with visible light and under sensitized energy transfer conditions. This new excited state reactivity in aryl‐maleimides is deciphered through photochemical, photophysical, and spectroscopic studies. The stereochemistry of the photodimer depends on the type of non‐bonding interactions prevalent during photodimerization which is in turn dictated by the substituents on the maleimide ring. More importantly, the stereochemistry of the photodimer formed is complementary to the product observed under thermal conditions. [ABSTRACT FROM AUTHOR]

This account highlights the role of restricted bond rotations in influencing the excited-state reactivity of organic molecules. It highlights the photochemical reactivity of various organic molecules and the design strategies that could be exploited by chemists to utilize restricted bond rotations to uncover new excited-state reactivity and to achieve selectivity. 1 Introduction. 2 NEER-Principle and Restricted Bond Rotations in the Excited State 3 [2+2]-Photocycloaddition of Enamides 4 [3+2]-Photocycloaddition vs. Paternò–Büchi Reaction of Enamides 5 Divergent Photoreactivity of Enones Dictated by Restricted Bond Rotations: Norrish–Yang reactions vs. 6π-Photocyclization 6 Divergent Photoreactivity of Imides with Alkenes: [2+2]-Photocycloaddition vs. Photoene Reaction 7 Summary and Outlook [ABSTRACT FROM AUTHOR]

Hydrogen bonding mediated control of photochemical reactions is highlighted with an eye towards the development of Brønsted acid mediated photocatalysis. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]