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Conformational Dynamics of Charge‐Transfer States in Donor−Bridge−Acceptor Systems
Author(s) -
Lauteslager Xavier Y.,
van Stokkum Ivo H. M.,
van Ramesdonk H. John,
Bebelaar Dick,
Fraanje Jan,
Goubitz Kees,
Schenk Henk,
Brouwer Albert M.,
Verhoeven Jan W.
Publication year - 2001
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/1099-0690(200108)2001:16<3105::aid-ejoc3105>3.0.co;2-i
Subject(s) - chemistry , acceptor , piperazine , chromophore , photochemistry , piperidine , excited state , solvatochromism , electron donor , fluorescence , photoinduced charge separation , stereochemistry , molecule , organic chemistry , physics , quantum mechanics , photocatalysis , nuclear physics , artificial photosynthesis , condensed matter physics , catalysis
Donor−acceptor compounds containing a phenylenediamine electron donor and a naphthalene, a cyanobenzene, or a cyanonaphthalene acceptor were studied. The two chromophores are connected by three different bridging units, consisting of CH 2 groups linked to a semiflexible piperidine or piperazine ring or to a rigid 2,5‐diazabicyclo[2.2.1]heptane group. All donor−acceptor compounds show photoinduced charge separation, resulting in the formation of a compact charge‐transfer (CCT) state in nonpolar solvents. The conformational change needed to arrive at this species is impossible in a nonpolar polymer matrix and also in methylcyclohexane at low temperature. In the cases of the piperidine‐ and piperazine‐bridged donor−acceptor compounds, evidence for the involvement of an extended charge‐transfer (ECT) species as a precursor of the CCT species was obtained from time‐resolved fluorescence measurements. In contrast to harpooning systems studied previously, the energy differences between the species in the present case are so small that their interconversions are reversible within the excited state lifetimes.