Conformational Dynamics of Charge-Transfer States in Donor−Bridge−Acceptor Systems

Abstract

Donor−acceptor compounds containing a phenylenediamine electron donor and a naphthalene, a cyanobenzene, or a cyanonaphthalene acceptor were studied. The two chromophores are connected by three different bridging units, consisting of CH 2 groups linked to a semiflexible piperidine or piperazine ring or to a rigid 2,5-diazabicyclo[2.2.1]heptane group. All donor−acceptor compounds show photoinduced charge separation, resulting in the formation of a compact charge-transfer (CCT) state in nonpolar solvents. The conformational change needed to arrive at this species is imposs-

Synthesis and Evaluation of Cyclic Secondary Amine Substituted Phenyl and Benzyl Nitrofuranyl Amides as Novel Antituberculosis Agents

“…The fluorine of 3 or 4-fluoro nitrobenzene (6 and 7) was first substituted by conventional aromatic nucleophilic displacement with secondary amides morpholine, 1-methyl-piperazine, 1-benzyl piperazine, 4-benzyl piperadine and 1-(2-pyridyl) piperazine to give corresponding substituted nitrobenzenes 12a-j with yields ranging 78%-95%. 8 It was noted that the substitution of p-fluoro nitrobenzene was faster than m-fluoro nitrobenzene, 8 hrs compared with 24 hrs, respectively. The nitro functional group of compounds 12a-j, except compounds 12c and 12h, was reduced by catalytic hydrogenation to give the corresponding anilines 13a-j in quantitative yields.…”

An Experimental and Computational Study on Intramolecular Charge Transfer: A Tetrathiafulvalene‐Fused Dipyridophenazine Molecule

“…[24] The Lippert-Mataga plot for TTF-dppz conjugate 1 is shown in Figure 7. From the slope of this plot, the difference of the dipole moment between the excited state and the ground state is estimated to be 16 Debye.…”

Intramolecular excimer and exciplex emission of 1,4-dipyrenyl substituted cyclohexasilane

“…In order to obtain a better understanding of the dynamics and energetics of excimer formation, a global target analysis [8,14] of the streak camera fluorescence data of 2 was performed. The data were fitted with a number of two-state equilibrium models (Fig.…”

“…Steady-state UV and fluorescence spectra were recorded on Cary 1 and Spex Fluorolog instruments, respectively [7]. Time-resolved fluorescence spectra were collected on streak camera [8] or optical multichannel analyzer [9] systems described elsewhere. For all fluorescence measurements samples were degassed by purging with argon for 15 min.…”

“…The result that k 12 ¼ k 21 can be interpreted by assuming that the silicon ring is undergoing conformational changes at this rate, thereby moving the pyrenyl substituents in and out of a position in which they give excimer emission. In this respect, the situation is different from the folding process of cyclic systems in the charge separated excited state of electron donor-acceptor molecules [8,14,20,21], which is driven by the coulombic attraction of oppositely charged chromophores. As conformational barriers in cyclohexasilanes are much lower than those in cyclohexanes it would be interesting to investigate whether dipyrenyl substituted cyclohexanes are also able to undergo intramolecular excimer formation.…”