Effect of nonproximate atomic substitution on excited state intramolecular proton transfer

✍ Scribed by ?uma, Martin; Thompson, Clifton; Scheiner, Steve

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 223 KB
• Volume: 19
• Category: Article
• ISSN: 0192-8651
• DOI: 10.1002/(sici)1096-987x(19980130)19:2<129::aid-jcc5>3.0.co;2-w

✦ Synopsis

The central C atom of the OCCCO skeleton of the malonaldehyde molecule is replaced by N, and the effects upon the intramolecular H-bond and the proton transfer are monitored by ab initio calculations in the ground and excited electronic states. The H-bond is weakened in the singlet and triplet states 6 arising from n * excitation in both molecules, which is accompanied by a heightened barrier to proton transfer. 3 * behaves in the same manner, but the singlet * state has a stronger H-bond and lower barrier. Replacement of the central C atom by N strengthens the intramolecular H-bond. Although the proton transfer barrier in the ground state of formimidol is lower than in malonaldehyde, the barriers in all four excited states are higher in the N-analog.

6 The latter substitution also dampens the effect of the n * excitation upon the H-bond and increases the excitation energies of the various states, particularly *.