Steric hindrance in the gas phase singlet electronic energy transfer: From naphthalene to the t r a n s-azobutane isomers

Abstract
The singlet intermolecular energy transfer rates from naphthalene (S1, ∼91 kcal/mol) to the various trans‐azobutane isomers have been measured in the gas phase. The first excited singlet states of these azobutane isomers lie below ∼70 kcal/mol. The rate constants for singlet collisional energy transfer (kc) are 30.3±2.6, 18.9±0.9, 12.6±1.0, and 3.2±0.3 in units of 1010 M−1⋅sec−1, for the accepter series azo‐n‐butane, azoisobutane, azo‐sec‐butane, and azo‐tert‐butane, respectively. The tenfold decrease in the rates of energy transfer through this series have been attributed to increasing steric inhibition of the electron exchange contribution to singlet–singlet electronic energy transfer.

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