Novel Chiral Pyromellitdiimide (1,2,4,5-Benzenetetracarboxydiimide) Dimers and Trimers: Exploring Their Structure, Electronic Transitions and Exciton Coupling
Artikel i vetenskaplig tidskrift, 2002

The chiral but highly symmetrical acyclic and cyclic pyromellitic diimide dimers and trimers 2-5 have been obtained and characterized for the first time. The pyromellitdiimide chromophores in these molecules are linked by a rigid diequatorially 1,2-disubstituted cyclohexane skeleton. The structures of the compounds have been determined in detail by molecular modeling and, in the case of cyclic dimer 4 and trimer 5, by means of X-ray diffraction analysis. The electronically excited states of the pyromellitdiimide chromophore (1a) have been studied in these and other model compounds by means of linear dichroism (LD), magnetic circular dichroism (MCD), and circular dichroism (CD) spectroscopy. CD spectra of the rigid cyclic trimer 5 have provided the most detailed information on the excited states of the pyromellitdiimide chromophore. The low-energy tail (340-360 nm) of the absorption envelope can be assigned to out-of-plane polarized n-pi* transitions (I, II). The higher energy bands are due to contributions from up to six pi-pi* transitions, these being polarized either along the long (IV-VI, VIII) or short axis (III, VII). The results of ab initio CIS/cc-pVDZ and semiempirical INDO/S-CI calculations have been compared with the experimental data. CD Cotton effects in the region 200260 nm, which result from exciton interactions between electric dipole allowed transitions of two pyromellitdiimide chromophores in compounds 2-5, provide reliable and useful information concerning the conformation and absolute configuration of these molecules, which may be extrapolated to other oligoimide systems.

chirality

pyromellitic diimides

circular dichroism

electronic transitions

Författare

J. Gawronski

M. Brzostowska

K. Gawronska

J. Koput

U. Rychlewska

P. Skowronek

Bengt Nordén

Institutionen för fysikalisk kemi

Chemistry - A European Journal

0947-6539 (ISSN) 1521-3765 (eISSN)

Vol. 8 2484-2494 and ibid. 2833

Styrkeområden

Nanovetenskap och nanoteknik

Energi

Livsvetenskaper och teknik

Materialvetenskap

Ämneskategorier

Fysikalisk kemi

Fundament

Grundläggande vetenskaper

DOI

10.1002/1521-3765(20020603)8