Jump to main content
Jump to site search

Issue 5, 2000
Previous Article Next Article

Internal conversion in 4-substituted 1-naphthylamines. Influence of the electron donor/acceptor substituent character

Author affiliations


The thermally activated internal conversion (IC) taking place in 4-substituted 1-(dimethylamino)naphthalenes (14DMX) and 1-aminonaphthalenes (14ANX) with X=CN, Cl, H, CH3 and OCH3 was investigated in three solvents spanning the polarity scale, hexane, diethyl ether and acetonitrile. In both series 14DMX and 14ANX, the efficiency of the IC reaction decreases substantially when X changes from CN to OCH3, the order in which the electron donor character of the 4-substituent increases. Considerably larger IC reaction rate constants are obtained for the first group of compounds. This difference is connected with the ground state structure of the amino group, which is more strongly twisted for 14DMX (ca. 60°) than for 14ANX (ca. 20°), whereas both sets of 1-naphthylamines are planarised in the S1 excited state. The IC process slows down with increasing solvent polarity for each of the 14DMX and 14ANX molecules. The substituent X and the solvent polarity mainly affect the IC activation energy EIC. With 14DMX in hexane, EIC increases from 10 kJ mol−1 for X=CN to 34 kJ mol−1 for X=OCH3, whereas with, e.g., 14DMCL a solvent polarity dependent increase of EIC from 16 kJ mol−1 in hexane to 28 kJ mol−1 in acetonitrile is observed. The height of the barrier EIC is governed by the energy gap ΔE(S1,S2) between the two lowest excited singlet states. The influence of ΔE(S1,S2) on EIC is attributed to vibronic coupling caused by the proximity of the S1 and S2 states, which flattens the S1 potential energy surface and thereby lowers the IC barrier when ΔE(S1,S2) becomes smaller. It is assumed that the IC reaction of the 1-naphthylamines passes through a conical intersection, which exists as a consequence of the relative displacement of the S1 and S0 surfaces caused by the different amino twist angles in the two states.

Back to tab navigation

Publication details

The article was received on 09 Nov 1999, accepted on 20 Dec 1999 and first published on 16 Feb 2000

Article type: Paper
DOI: 10.1039/A908924A
Citation: Phys. Chem. Chem. Phys., 2000,2, 981-991
  •   Request permissions

    Internal conversion in 4-substituted 1-naphthylamines. Influence of the electron donor/acceptor substituent character

    K. Suzuki, A. Demeter, W. Kühnle, E. Tauer, K. A. Zachariasse, S. Tobita and H. Shizuka, Phys. Chem. Chem. Phys., 2000, 2, 981
    DOI: 10.1039/A908924A

Search articles by author