Theoretical Investigation of Luminescence Behavior as a Function of Alkyl Chain Size in 4-Aminobenzonitrile Alicyclic Derivatives
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- 作者：Isabel Gó ; mez ; Yannick Mercier ; Mar Reguero
- 刊名：Journal of Physical Chemistry A
- 出版年：2006
- 出版时间：October 12, 2006
- 年：2006
- 卷：110
- 期：40
- 页码：11455 - 11461
- 全文大小：264K
- 年卷期：v.110,no.40(October 12, 2006)
- ISSN：1520-5215
文摘
There is still controversy about the structure of the intramolecular charge transfer (ICT) emitting species in
-electron donor-acceptor systems that show dual fluorescence. Although the twisted ICT model is quitegenerally accepted, the planar ICT model is not ruled out because firm experimental evidence supports it.Among these it is the fact that some rigidized systems such as bicyclic 4-aminobenzonitrile derivatives exhibitdual fluorescence. We present here an ab initio CASSCF/CASPT2 study of a series of these compounds withthe alicyclic chain ranging from 5 to 7 carbon atoms and compare their ICT mechanism with the more flexible4-aminobenzonitrile (ABN) and 4-(dimethylamino)benzonitrile (DMABN). We present the energetics,geometries, and valence bond structures of the critical points of the potential-energy surfaces of the ground,local excited (LE), and ICT states. Our results show that the photophysical differences of the studied systemsmay be rationalized by two factors: the position of the ICT and LE potential-energy surfaces at the firststages of the ICT reaction and the relative energies of the excited-state minima. Computational evidence ispresented that a twisted ICT structure can be adopted in some molecules such as NXC6 and NXC7 and thatthe anomalous band of the fluorescence spectra of these systems is emitted from a twisted ICT species.
-electron donor-acceptor systems that show dual fluorescence. Although the twisted ICT model is quitegenerally accepted, the planar ICT model is not ruled out because firm experimental evidence supports it.Among these it is the fact that some rigidized systems such as bicyclic 4-aminobenzonitrile derivatives exhibitdual fluorescence. We present here an ab initio CASSCF/CASPT2 study of a series of these compounds withthe alicyclic chain ranging from 5 to 7 carbon atoms and compare their ICT mechanism with the more flexible4-aminobenzonitrile (ABN) and 4-(dimethylamino)benzonitrile (DMABN). We present the energetics,geometries, and valence bond structures of the critical points of the potential-energy surfaces of the ground,local excited (LE), and ICT states. Our results show that the photophysical differences of the studied systemsmay be rationalized by two factors: the position of the ICT and LE potential-energy surfaces at the firststages of the ICT reaction and the relative energies of the excited-state minima. Computational evidence ispresented that a twisted ICT structure can be adopted in some molecules such as NXC6 and NXC7 and thatthe anomalous band of the fluorescence spectra of these systems is emitted from a twisted ICT species.