US EPA

3243823 

Journal Article 

Ultrafast intersystem crossing in 1-nitronaphthalene. An experimental and computational study 

Zugazagoitia, JS; Almora-Diaz, CX; Peon, J 

2008 

1 

Journal of Physical Chemistry A
ISSN: 1089-5639
EISSN: 1520-5215 

112 

3 

358-365 

English 

18166024 

10.1021/jp074809a 

WOS:000252483300003 

Previous studies have established that the major pathway
for the first singlet excited state of 1-nitronaphthalene is intersystem crossing to the triplet
manifold. In this contribution we present determinations of the decay of the S, state of this
compound in several solvents to establish the time scale of the multiplicity change as a function
of the polarity and hydrogen-bonding ability of the solvent environment. The measurements were
made with the femtosecond frequency up-conversion technique to follow the weak spontaneous
molecular emission which precedes triplet formation. Our results show that in all environments
the S, lifetime is 100 fs or less, making 1-nitronaphthalene the organic compound with the
fastest multiplicity change ever measured. We also show that the bathochromic shifts observed for
the first absorption band imply changes in the relative energies of the singlet and triplet
manifolds, which in turn manifest in a 2-fold increase of the fluorescence lifetime in
cyclohexane compared with the polar solvents. Additionally, we performed excited-state
calculations at the TD-DFT/PBE0/6-311++G(d,p) level of theory with the PCM model for solvation.
The TD-DFT theory identifies the presence of upper triplet states which can act as receiver
states in this highly efficient photophysical pathway. Together, the experimental and theoretical
results show that the dynamics of the Si state in 1-nitronaphthalene represent an extreme
manifestation of El-Sayed's rules due to a partial (n-pi*) character in the receiver triplets
which are nearly isoenergetic with S-1, determining a change in the molecular spin state within
100 fs.