Conformational dynamics and charge separation in the excited state of bridged donor–acceptor compounds

✍ Scribed by J. W. Verhoeven; B. Wegewijs; T. Scherer; R. P. H. Rettschnick; J. M. Warman; W. Jäger; S. Schneider

• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: English
• Weight: 929 KB
• Volume: 9
• Category: Article
• ISSN: 0894-3230
• DOI: 10.1002/(sici)1099-1395(199606)9:6<387::aid-poc787>3.0.co;2-3

✦ Synopsis

The process of intramolecular charge separation was studied in three nearly identical donor-bridge-acceptor compounds (1-3) under jet-cooled conditions. Each consists of a vinylcyanonaphthalene group as a powerful electron acceptor and an anilino derivative as an electron donor, separated by a rigid hydrocarbon bridge. The only difference between the three compounds is the substituent at the para position of the anilino group, which directly influences the ionization potential of the donor. For compound 1, which has the weakest donor of the three, it is found that excitation at (or very near) the electronic origin of the acceptor chromophore results exclusively in local emission, while excitations with an excess energy >60 cm" lead to a distinct red shift. Comparison with 2 and 3 shows that the red-shifted band can be attributed to a charge-separated state with an extended conformation, in which an electron has been transferred across three sigma bonds. Interestingly, this charge separation process appears to be more efficient in 2 and 3 than in 1, resulting in complete quenching of the local emission even at the lowest energy excitations. These observations are interpreted in terms of intramolecular radiationless transition theory and a comparison is made with the behaviour of (semi)flexibly bridged systems in which charge separation was shown earlier to be linked to a major, electrostatically driven reorganization.