Chemical vapor sensing, luminescence pH sensing, solvatochromism and photoisomerization of phenylene-vinylene derivatized terpyridine molecules
Description
Photophysics of fluorescent dyes is a field of constant interest because a better understanding of the excited-state properties helps in the design of new molecules as fluorescent probes for sensing and highly luminescent materials, especially for organic light emitting devices. Organic compounds with extended pi-systems, conjugated polymers, well defined oligomers have become an important class of electronic materials. The polypyridine complexes have been studied for their wide applications in varied fields. Introduction of fluorescence properties to the terpyridine and pyridine derivatives via linking them to phenylene vinylenes might open the way for further application as a new series of photofunctional compounds This work deals with the synthesis of some phenylene vinylene terpyridine/pyridine molecules, studying their photophysics and then demonstrating their ability for sensing applications Photophysical properties of phenylene-vinylene terpyridine/pyridine systems has been studied. These properties can be tuned by varying the donor and acceptor moieties in these systems. One such molecule is the MNpvpt, which has a strong electron-donating Me2N- group at one end and an electron accepting terpyridine at the other. The luminescence of this complex is highly solvatochromic, ranging from blue emission in hexane (lambdaem = 450 nm) to red emission in dimethylsulfoxide (lambda = 630 nm) with high quantum yields (0.65) in most organic solvents. This solvatochromic chromophore was incorporated into polymer matrices of polystyrene (PS) and polymethylmethacrylate (PMMA) and thin films of this was coated on quartz. Films containing the MNpvpt chromophore exhibit blue luminescence in air and, interestingly, exhibit rapid and reversible changes in the luminescence maxima in the presence of vapors of a wide variety of solvents MNpvpt contains two different types of nitrogen donors, i.e. , the hetero aromatic donors and the aliphatic amine group, as potential binding site for acidic protons and/or metal cations. This property was exploited and films containing the MNpvpt chromophore show interesting effects of vapors of acid and base on the emission of the ligand due to protonation and deprotonation at the potential binding sites. To further understand this a detailed study of the acid-base chemistry of MNpvpt and its analogue pvpt in solution was carried out. These experiments yielded the ground and excited state pka's of these molecules which gave a better understanding of their behavior in films. The surface morphology of these films were looked at using profilometry and AFM Photoisomerization of phenylene-vinylene terpyridine/pyridine is an interesting phenomenon. Effect of solvent polarity, acceptor group and donor group on isomerization has been studied Time Dependent Density Functional (TDDFT) calculations were employed to study excited state properties, affect of protonation and charge transfer characteristics of some of these systems using Gaussian 03. These calculations correlated reasonably well with experimental results and gave a good understanding of the structural and electronic factors associated with these molecules