TY - JOUR TI - Molecular Mechanism of Diaminomaleonitrile to Diaminofumaronitrile Photoisomerization: An Intermediate Step in the Prebiotic Formation of Purine Nucleobases AU - Szabla, Rafał AU - Góra, Robert W. AU - Šponer, Jiří AU - Šponer, Judit E. T2 - Chemistry – A European Journal AB - The photoinduced isomerization of diaminomaleonitrile (DAMN) to diaminofumaronitrile (DAFN) was suggested to play a key role in the prebiotically plausible formation of purine nucleobases and nucleotides. In this work we analyze two competitive photoisomerization mechanisms on the basis of state-of-the-art quantum-chemical calculations. Even though it was suggested that this process might occur on the triplet potential-energy surface, our results indicate that the singlet reaction channel should not be disregarded either. In fact, the peaked topography of the S1/S0 conical intersection suggests that the deexcitation should most likely occur on a sub-picosecond timescale and the singlet photoisomerization mechanism might effectively compete even with a very efficient intersystem crossing. Such a scenario is further supported by the relatively small spin–orbit coupling of the S1 and T2 states in the Franck–Condon region, which does not indicate a very effective triplet bypass for this photoreaction. Therefore, we conclude that the triplet reaction channel in DAMN might not be as prominent as was previously thought. DA - 2014/// PY - 2014 DO - 10.1002/chem.201304224 DP - Wiley Online Library VL - 20 IS - 9 SP - 2515 EP - 2521 J2 - Chem. Eur. J. LA - en SN - 1521-3765 ST - Molecular Mechanism of Diaminomaleonitrile to Diaminofumaronitrile Photoisomerization UR - http://onlinelibrary.wiley.com/doi/10.1002/chem.201304224/abstract Y2 - 2014/02/27/09:15:44 KW - Quantum chemistry KW - isomerization KW - nucleobases KW - nucleotides KW - photochemistry ER -