الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 160 |  |  |
| | | from | 160 | | |
Abstract
The observation of solvent induced shifts of the absorption and fluorescence emission bands has been used extensively in order to study the changes in electronic distribution in excited states of solute molecules. An understanding of excited state properties helps not only in the design of new molecules but also for the best performance for specific application. Photoinduced intramolecular charge transfer (ICT) is one of the most widely studied phenomena as a primary function for photoelectronic devices. It is well known that the local environment, especially solvents, has a profound effect on the emission behaviour of ICT-type compounds. Molecules undergoing ICT often exhibit a large change in dipole moment in the excited state when compared with the ground state. As a result, these systems often show systematic variation of the fluorescence properties with solvent polarity.
Conjugated donor-(-spacer)-acceptor (D––A) have attracted tremendous research interest. Such push–pull systems usually show intramolecular charge-transfer (ICT) characteristics which is responsible for the polarization of these compounds and generation of a molecular dipole. The notable spectral and electrical properties of such systems make them promising materials in many applications such as fluorescent biochemical probes, photovoltaic cells and organic light-emitting diodes (OLEDs).
Proper choice of a strong electron donating group, strong electron withdrawing acceptor and suitable -spacer is expected to enhance the charge transfer properties of the D--A fluorophore. 2,2’-bithiophene and its derivatives were reported to be among the most suitable structures for modeling of push-pull fluorophores due to the long-chain conjugation with substituents in 5 and 5’-positions.
In this study, 2,2’-bithiophene is linked to cyano group as an electron acceptor group for its strong electron-withdrawing ability in case of DMTTC
(5-(5-(3,5-dimethoxyphenyl) thiophen-2-yl) thiophene-2-carbonitrile) and
2-carboxamidine group in case of DMTTCA (5-(5-(3,5-dimethoxyphenyl) thiophen-2-yl)thiophene-2-carboxamidine hydrochloride salt) and m-dimethoxyphenyl groups as an electron donor to examine the effect of such structural changes on the extent of the intramolecular charge transfer (ICT) characteristics in both compounds. Therefore, photophysical properties of DMTTC and DMTTCA were studied in a variety of protic and aprotic solvents and correlated with a number of solvent parameters such as the solvent polarity parameters ”E” _”T” ^”N” and the reaction field factor f. Three linear solvation energy relationships developed by Kamlet-Taft , Catalán, and Laurence. were also employed to assess the effect of specific and non-specific interactions on the ICT characteristics in DMTTC and DMTTCA.