A dramatic effect of the donor ionization potential on the apparent barrier to intramolecular exciplex formation in jet-cooled, bichromophoric molecules

✍ Scribed by B. Wegewijs; A.K.F. Ng; R.P.H. Rettschnick; J.W. Verhoeven

• Publisher: Elsevier Science
• Year: 1992
• Tongue: English
• Weight: 616 KB
• Volume: 200
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(92)87003-8

✦ Synopsis

The fluorescence of three nearly identical donor-bridge-acceptor molecules was studied under jet-cooled conditions. These compounds contain a I-cyanonaphthalene group as an electron acceptor (A) and an aniline derivative as an electron donor (D). Their only difference is in the substituent on the para position of the anilinogroup and therefore in ionization potential (IP). D and A are interconnected by a saturated hydrocarbon bridge of limited flexibility, which holds D and A far apart in the electronic ground state. Nevertheless, an intramolecular exciplex is formed upon excitation of the cyanonaphthalene group with sufficient excess vibrational energy. The barrier to this exciplex formation appears to be much lower than the barrier predicted for folding the bridge to bring D and A in close contact and moreover, the molecule with the lowest IP has by far the lowest barrier. This is taken as conclusive evidence that long-range electron transfer is the first step in the exciplex formation and determines the height of the barrier. The subsequent folding of the bridge would then be a result of the Coulombic attraction forces between D and A.