Photoinduced coupled twisted intramolecular charge transfer and excited-state proton transfer via intermolecular hydrogen bonding: a DFT/TD-DFT study

We discuss theoretically the geometric and electronic structure properties of the thiazolidinedione derivative A and its hydrogen-bonded complex in dimethylformamide (DMF) solution in the S0 and S1 states. To gain insight into the photoinduced coupled excited-state proton transfer (ESPT) and twisted intramolecular charge transfer (TICT) associated with intermolecular hydrogen bonding, the potential energy profiles are provided along the Osingle bondH bond and the twisted angle. It is predicted that TICT in S1 can facilitate ESPT initiated by intermolecular hydrogen-bond strengthening in the S1 state. The coupling of ESPT and TICT is energetically preferable

The Influence of Reaction enthalpy on the Formation of “Twisted Intramolecular Charge Transfer" (TICT)-States in Inert Solvents: p-Substituted N,N-Dimethylanilines

In saturated hydrocarbons dual fluorescence appears both in p-N,N-Dimethylaminobenzonitrile (DMABN) and p-N,N-Dimethylaminoethylbenzoate (DMABEE). The temperaturedependence of the fluorescence quantum yield suggests that in DMABEE E(B*) ≈ E(TICT) and in DMABN E(B*) <E(TICT)

Do fluorescence and transient absorption probe the same intramolecular charge transfer state of 4- ( dimethylamino ) benzonitrile?

We present here the results of time-resolved absorption and emission experiments for 4-(dimethylamino)benzonitrile in solution, which suggest that the fluorescent intramolecular charge transfer (ICT) state may differ from the twisted ICT (TICT) state observed in transient [email protected]

Influence of geometry on the emitting properties of 2,3-naphthalimides

The luminescence properties of 2,3-naphthalimides have been studied using picosecond and nanosecond spectroscopies. In acetonitrile solution N-phenyl-2,3-naphthalimid(e3 ) is found to emit dual fluorescence with emission maxima at 385 and 490 nm, respectively. The short-wavelength emission corresponds to the known fluorescence of the naphthalimides and is demonstrated for 3 to originate from a molecular conformation in which the phenyl substituent and the naphthalimide skeleton are orthogonal to each other. The long-wavelength emission is assumed to originate from a singlet excited state formed by a ca. 90° rotation of the phenyl group so that the two moieties are coplanar. Only a small dipole moment change is found between this excited state and the ground state. Only short-wavelength emission is observed with a lifetime in the nanosecond range as in the case of 1 and 2 when phenyl rotation is blocked with a bulky ortho tert-butyl group (compound 4). Increasing the viscosity of a glycerol/ethanol medium enhances both the efficiency and the lifetime of the short-wavelength emission of 3. It appears that at 77 K the emission originates directly from the Franck-Condon state. At room temperature, the other two emitting species are shown to arise from the Franck-Condon state by competitive intramolecular geometrical relaxation processes. Structures 5 and 6 are tentatively put forward to explain the formation of naphthazepinedione 8 by a 2 \pi + 2 \pi photochemical cycloaddition reaction

Twisted Intramolecular Charge Transfer in Protonated Amino Pyridine

International audienceThe excited state properties of protonated ortho (2-), meta (3-) and para (4-) aminopyridine molecules have been investigated through UV photo fragmentation spectroscopy and excited state couple cluster CC2 calculations. Cryogenic ion spectroscopy allows recording well-resolved vibronic spectroscopy that can be nicely reproduced through Franck Condon simulations of the pp* local minimum of the excited state potential energy surface. The excited state lifetimes have also been measured through a pump-probe excitation scheme and compared to the estimated radiative lifetimes. Although protonated aminopyridines are rather simple aromatic molecules, their deactivation mechanisms are indeed quite complex with unexpected results. In protonated 3-and 4-aminopyridine, the fragmentation yield is negligible around the band origin, which implies the absence of internal conversion to the ground state. Besides, a twisted intramolecular charge transfer reaction is evidenced in protonated 4-aminopyridine around the band origin, while excited state proton transfer from the pyridinic nitrogen to the adjacent carbon atom opens with roughly 500 cm-1 of excess energy

Interaction of anticancer reduced Schiff base coumarin derivatives with human serum albumin investigated by fluorescence quenching and molecular modeling

The specific binding of five reduced Schiff base derived 7-amino-coumarin compounds with antitumor activity to human serum albumin, the principal binding protein of blood, was studied by fluorescence spectroscopy. Their conditional binding constants were computed and the reversible binding at the Sudlow’s site I was found to be strong (KD ~ 0.03-2.09 M). Based on the data albumin can provide a depot for the compounds and is responsible for their biodistribution and transport processes. The experimental data is complemented by protein– ligand docking calculations for two representatives which support the observations. The proton dissociation constants of the compounds were also determined by UV-Vis spectrophotometric and fluorometric titrations to obtain the actual charges and distribution of the species in the various protonation states at physiological pH

Three predictions on July 2012 Federal Elections in Mexico based on past regularities

Electoral systems are subject of study for physicist and mathematicians in last years given place to a new area: sociophysics. Based on previous works of the author on the Mexican electoral processes in the new millennium, he found three characteristics appearing along the 2000 and 2006 preliminary dataset offered by the electoral authorities, named PREP: I) Error distributions are not Gaussian or Lorentzian, they are characterized for power laws at the center and asymmetric lobes at each side. II) The Partido Revolucionario Institucional (PRI) presented a change in the slope of the percentage of votes obtained when it go beyond the 70% of processed certificates; hence it have an improvement at the end of the electoral computation. III) The distribution of votes for the PRI is a smooth function well described by Daisy model distributions of rank $r$ in all the analyzed cases, presidential and congressional elections in 2000, 2003 and 2006. If all these characteristics are proper of the Mexican reality they should appear in the July 2012 process. Here I discuss some arguments on why such a behaviors could appear in the present processComment: 6 pages, one tabl

A Theoretical Investigation of Charge Transfer in Several Substituted Acridinium Ions

We present calculations for various properties of the ground and excited states of several arylamine-substituted acridinium ion systems that have been studied experimentally. Using ab initio and semiempirical quantum mechanical methods together with the generalized Mulliken−Hush (GMH) model, we examine the excitation energies, dipole moment shifts, and electronic coupling elements for the vertical charge shift (CSh) processes in these systems. We also examine solvent effects on these properties using a dielectric continuum reaction field model. The results are in generally good agreement with available experimental results and indicate that there is strong electronic coupling in these systems over a wide range of torsional angles. Nevetheless, the initial and final cationic states remain reasonably well-localized over this range, and thus TICT state formation is unlikely in these systems. Finally, a version of the GMH model based on Koopmans\u27 Theorem is developed and found to yield coupling elements generally within a factor of 2 of the many-electron GMH for a sample acridinium system, but with overestimated adiabatic and diabatic dipole moment differences

生体分子の簡易検出を目指した凝集誘起発光色素ラベル化プローブの開発と検出メカニズムの解明

バイオイメージングやバイオマーカーの検出による診断には蛍光色素が汎用されるが、そうした手法にはいくつかの問題点がある。その中でも、濃度消光の問題は一般の蛍光色素においては本質的なデメリットであり、このことが検出感度の壁となっている場合が多い。そこで、本研究では、濃度消光とは逆に凝集によって蛍光強度が劇的に増大する凝集誘起発光（AIE）色素を用いて疾患の診断を行う手法の開発を行い、その検出メカニズムを明らかにすることを目的とした。ターゲットとする疾患として、罹患者数が多く社会的影響が大きいガンとアルツハイマー病（AD）を選び、それぞれのバイオマーカーと考えられるテロメア鎖およびアミロイドβ（A）の検出を行った。テロメア鎖に対するプローブとして、AIE色素で修飾した相補鎖DNAまたはPNAを用いたところ、どちらのプローブでも高い感度でテロメア鎖の定量が可能であることが示された。しかし、プローブがDNA の場合にはテロメア量に比例して蛍光強度が増加するのに対しPNAをプローブとした場合には、逆に濃度依存的に蛍光強度が弱くなった。これは、PNAの疎水性によりプローブ自身が凝集することで生じた強い蛍光が、二重鎖形成とともに分散して消光されたためであることを明らかにした。また、DNAプローブを用いた結果の考察から、AIE色素の周辺に分子運動を阻害するダングリングエンドまたは二重鎖が存在することが、蛍光増大の要件であることが示唆された。次に、ADのマーカーであるAの検出を行った。プローブとして、アミロイド繊維化促進ペプチド（AFPP）にAIE色素を結合させた化合物（AIE-AFPP）を用いた。AIE-AFPPはAFPP自身と同様にAの繊維化を促進するとともに、Aと共凝集することで濃度依存的にAIEの蛍光増大が観測され、短時間で容易にAの定量が可能であることが示された。この手法によるAの検出限界は4.2 nMであり、この値はELISAには及ばないが、プローブ合成およびassayの簡便性や、測定者に高いスキルを要求しない点において優れた手法である。本研究の結果は、AIE色素をシグナル発信部位としてもつプローブを用いることで、生体分子を高感度かつ簡便に定量可能であることを示している。また、本研究で明らかにされた蛍光増大のメカニズムは、ターゲットにあわせたプローブの分子設計と、安価・簡便・高感度・ハイスループットな検出システムの構築のための指針を与えると考えられる。甲南大学平成27年(2015年度