|M.Sc Student||Kuznetz Olga|
|Subject||Photophysical Properties of Materials Potentially Relevant|
for Molecular Logic Gates
|Department||Department of Chemistry||Supervisor||Professor Emeritus Shammai Speiser|
|Full Thesis text|
This thesis reports the photophysical characterization of organic molecules implementing molecular half and full adders. Organic molecules are promising candidates for the realization of nanometric electronic and photonic devices. They have nanometric dimensions, they can be easily produced, their properties can be tuned through chemical modifications.
The work deals with the investigation of the photophysical details of the Rhodamine 6G (Rh6G) and 4-azulene-1-yl-butylamine (Az-amine) two half adders and of the Rhodamine - Azulene (Rh - Az) bichromophoric full adder. The molecular logic circuits were characterized by the following techniques: steady state absorption and fluorescence, and Laser Induced Fluorescence (LIF) using Nd-YAG laser, operating at its second harmonic (532nm, 18797cm-1) and at first harmonic (1064 nm, 9398cm-1).
The transition energies of Rh6G, Azulene (Az), Rhodamine B isothiocyanate, Az - amine and Rh - Az molecules were established during the research, recognizing Rh - Az molecule as a bichromophoric one. Intramolecular Excited Energy Transfer (EET) from Rh moiety to Az one was observed. Intramolecular energy transfer yield (FET) from Rh to Az moiety was calculated from the absorption and fluorescence spectra of Rh - Az molecule, yielding FET=0.96. Intramolecular ET rate constant (kET) in Rh - Az molecule was 7.81·109 s-1.
In addition we have investigated the intermolecular EET from Rh6G (donor molecule) to Az (acceptor molecule). The critical transfer radius for this donor - acceptor pair was 96.60Å, typical of efficient long - range dipole - dipole interaction. The bimolecular quenching constant (kq) for this donor - acceptor pair was 5.44·1011 L·mol-1·s-1.
In the LIF experiments the following parameters were measured: emission intensities from S1 and S2 excited levels of Rh6G, S1àS0 and S2àS0 transition intensities of Rh-Az and of Az-amine molecules. The results indicated a consecutive two-photon absorption process: in Rh6G and in Rh-Az (for the Rh moiety) molecules, together with the photoquenching of the S1 excited state of the molecules. Two photon absorption in Rh6G, Az-amine and in Rh - Az molecules followed by photoquenching of S1 state and S2 fluorescence was observed due to laser excitation at 532 nm. The absorption cross section values for the S1àS2 transition in the molecules mentioned above were obtained using photoquenching “Stern - Volmer” plots.
LIF results enabled us to implement Rh6G and Az-amine half adders and Rh - Az molecular full adder. Experimental truth tables taking into consideration input and output threshold values, based on LIF and on steady state experiments, for half and full adders were constructed.