Excited States Of Organic Molecules Research Articles

Dual-rotor strategy for organic cocrystals with enhanced near-infrared photothermal conversion.

Organic cocrystal engineering provides a promising route to promote the near-infrared (NIR) light harvesting and photothermal conversion (PTC) abilities of small organic molecules through the rich noncovalent bond interactions of D/A units. Besides, the single-bond rotatable groups known as "rotors" are considered to be conducive to the nonradiative transitions of the excited states of organic molecules. Herein, we propose a single-/double-bond dual-rotor strategy to construct D-A cocrystals for NIR PTC application. The results reveal that the cocrystal exhibits an ultra-broadband absorption from 300 nm to 2000 nm profiting from the strong π-π stacking and charge transfer interactions, and the weakened p-π interaction. More importantly, the PTC efficiency of cocrystals at 1064 nm in the NIR-II region can be largely enhanced by modulating the number of rotor groups and the F-substituents of D/A units. As is revealed by fs-TA spectroscopy, the superior NIR PTC performance can be attributed to the nonradiative decays of excited states induced by the free rotation of the single-bond rotor (-CH3) from the donors and the inactive double-bond rotor ([double bond, length as m-dash]C(C[triple bond, length as m-dash]N)2) being in the active form of [-C(C[triple bond, length as m-dash]N)2] in the excited states from the acceptors. This prototype displays a promising route to extend the functionalization of small organic molecules based on organic cocrystal engineering.

Thioxanthone Dioxide Triplet States Have Low Oxygen Quenching Rate Constants.

With few exceptions, triplet excited states of organic molecules, 3M1, are quenched by ground state molecular oxygen, O2(X3Σg-), with rate constants kq greater than ∼109 M-1 s-1 in fluid solutions. If the energy of the triplet state is above 94 kJ/mol, then such quenching can result in the sensitized production of singlet oxygen, O2(a1Δg). In the interaction between 3M1 and O2(X3Σg-), the magnitudes of both kq and the yield of the O2(a1Δg) depend appreciably on mixing with the M-O2 charge-transfer state. Here, we report that triplet states of several thioxanthen-9-one-10,10-dioxide derivatives have unusually low kq values (as low as ∼1 × 108 M-1 s-1) but have quantum yields for the photosensitized production of O2(a1Δg) that approach unity. Because these molecules possess high oxidation potentials (∼3.5 V vs SCE), we suggest that charge transfer character in the 3M1-O2(X3Σg-) encounter complex is reduced, thereby lowering kq while maintaining high O2(a1Δg) yields. These results provide important experimental support for existing models for the quenching of organic molecule excited states by O2(X3Σg-).

SparseMaps-A systematic infrastructure for reduced-scaling electronic structure methods. VI. Linear-scaling explicitly correlated N-electron valence state perturbation theory with pair natural orbital.

In this work, a linear scaling explicitly correlated N-electron valence state perturbation theory (NEVPT2-F12) is presented. By using the idea of a domain-based local pair natural orbital (DLPNO), computational scaling of the conventional NEVPT2-F12 is reduced to near-linear scaling. For low-lying excited states of organic molecules, the excitation energies predicted by DLPNO-NEVPT2-F12 are as accurate as the exact NEVPT2-F12 results. Some cluster models of rhodopsin are studied using the new algorithm. Our new method is able to study systems with more than 3300 basis functions and an active space containing 12 π-electrons and 12 π-orbitals. However, even larger calculations or active spaces would still be feasible.

Proton transfer reactions: From photochemistry to biochemistry and bioenergetics

The present Review is an attempt by projecting the basic knowledge on photochemical proton transfer to achieve consistent understanding of proton motions in biocatalysis, photobiocatalysis, operation of selective proton channels and systems of photosynthesis and cellular respiration. The basic mechanisms of proton transfer are in active research in the electronic excited states of organic molecules. This allows observing the reactions directly in real time, providing their dynamic and thermodynamic description and coupling with structural and energetic variables. These achievements lay the background for understanding the proton transfers in biochemical reactions, where such ultrafast events are not only ‘optically silent’ but are hidden under much slower rate-limiting steps, such as protein conformational changes, substrate binding and product release. The mechanistic description of biocatalytic and transmembrane proton transport is shown as a multi-step proton migration that is available for modeling in photochemical reactions. For explaining the formation of transmembrane proton gradients, a simple ‘proton lift’ concept is presented that may be the basis of further research and analysis.

(Invited) High-Yield and Long-Lived Triplet Excited States of Pentacene Alkanethiolate Monolayer Protected Gold Nanoparticles By Singlet Fission

Photochemical conversion to high-yield and log-lived triplet excited states of organic molecules is an interesting research content. For example, three-dimensional self-assembled monolayers (SAMs) of organic dyes on metal nanoparticles (MNP) are highly promising as photofunctional nanomaterials. A major research topic is light energy conversion via photoinduced processes such as electron and energy transfer. The other application is optical molecular rulers (nanoruler) in the biological fields. In these cases, a serious problem of organic dye-modified SAMs on MNP is the significant deactivation pathway of the excited states of dyes caused mainly by the fast nanosurface energy transfer (NSET). Actually, more than 90% of fluorescence is quenched and formation of the excited triplet states is negligible. Therefore, the formation of high-yield and long-lived triplet excited states on MNP is favorable for various applications relaying on photoinduced processes. Generation of efficient singlet fission (SF) on gold nanoparticles (GNP) is a promising method to overcome the above-mentioned problem. SF is described as a spin-allowed process in which one singlet exciton splits into two triplet excitons.1 In our study, TIPS-pentacene-alkanethiolate monolayer-protected gold nanoparticles with different chain lengths and particle sizes were successfully synthesized to efficiently generate excited triplet states by singlet fission (Fig. 1). Time-resolved spectroscopy revealed high-yield excited triplet states by suppressing ET to the gold surface.2 The mean diameters (R CORE) of TP-C11-S-MPC and TP-C11-L-MPC are 1.65 ± 0.30 nm and 2.13 ± 0.33 nm, respectively. The core of TP-C11-S-MPC and TP-C11-L-MPC contains 158 and 338 Au atoms, respectively. Moreover, based on the values of elemental analysis, there are 51 and 75 TP molecules on one GNP. In addition, the coverage ratios of TP units (γ) to surface Au atoms in TP-C11-S-MPC and TP-C11-L-MPC are 63% and 51%, respectively. Steady-state absorption and fluorescence spectra of TP-Cn-X-MPCs and TP-Ref were measured in toluene. In absorption spectra (Fig. 2A), the spectral shape of TP-C11-S-MPC (spectrum a) matches well with that of TP-Ref (spectrum b).The fluorescence of TP-C11-S-MPC was strongly quenched relative to TP-Ref. To compare the emission spectral shapes, the fluorescence spectra of TP-C11-S-MPC (spectrum a) and TP-Ref (spectrum b) were normalized in Fig. 2B. The fluorescence excitation spectrum was observed (spectrum c in Fig. 2A) to carefully check the fluorescence species of TP-C11-S-MPC. Then, Fig. 2C shows the femtosecond transient spectra of TP-C11-S-MPC. After laser pulse excitation, the triplet–triplet absorption of TP units at ca. 520 nm develops, whereas the singlet–singlet absorption at ca. 630 nm decays. The maximum Φ Τ values attained 172 ± 26% and 157 ± 17% in TP-C11-S-MPC and TP-C7-S-MPC, respectively. [1] Hasobe, T. et al, J. Phys. Chem. A 2016, 120, 1867. [2] Hasobe, T. et al, Angew. Chem. Int. Ed. 2016, 55, 5230. Figure 1

Anomalous Perturbation of the O2 Sensitivity of Poly(aromatic) Hydrocarbons by Magnetic Quantum Dots

Molecular oxygen is known to be an efficient quencher of the excited states of organic molecules. This fact has been exploited to develop fluorescent O2 sensors, which is topical for cancer screening and many other applications. In this regard, our group and others have reported the development of robust, ratiometrically reporting chemosensors by conjugating O2-sensitive organic chromophores to inorganic quantum dots. Recently, an attempt was made to prepare a multifunctional sensor system by attaching the emissive poly(aromatic) hydrocarbons pyrene and perylene to magnetic nanomaterials, specifically CdSe/CdMnZnS and ZnSe/ZnMnS/ZnS quantum dots. However, the fluorescence of both dyes became invariant to oxygen levels even if the solutions were fully saturated. We ruled out any material dependency beyond the presence of Mn2+ ions by studying control samples, while molecular dynamics simulations negated any possibility of spatial sequestration of O2 by the magnetic fields. In the case of pyrene, the proxim...

The constructions and applications of purely organic phosphorescent material

Phosphorescence is among the many functional features of the excited organic molecules. Organic molecules with long-lived triplet excited states enable exciton migration over long distance, which is essential in a variety of optoelectronic applications such as photovoltaics, photocatalytic reactions, display and lighting system, molecular sensing and biological imaging. In general, phosphorescence materials involve the organometallic compounds that are expensive, such as Pt, Ir and so on. Owing to the presence of metal, the phosphorescence materials is toxic and are also intrinsically unstable in the case of high-energy blue emitters. Therefore the purely organic materials that show room-temperature phosphorescence (RTP) are attractive alternatives to organometallic phosphors. The triplet excitons are not commonly generated in organic materials and are mostly consumed through radiationless processes, such as vibrational dissipation and oxygen-mediated quenching, under ambient conditions. Recently, a variety of methods from molecular design to material design to access organic room temperature phosphorescence have been explored. This review focus on the recent advancements in the field of organic phosphorescence, classifying the strategies based on material design. The outlook of organic room temperature phosphorescence is also discussed. The basic concepts for RTP process are introduced to demonstrate what’s the key factors to obtain efficient RTP. They are: (1) the promotion of both singlet-to-triplet and triplet-to-singlet intersystem crossing, and (2) suppression of the nonradiative quenching processes from the triplet to the ground state. Comparisons between RTP and delayed fluorescence are also made in the review. The triplet excited states of organic molecules can be stabilized by interactions of host molecules and guest molecules, rigid solid-crystallized structures and the chromophore embedded in polymer, which can suppress the nonradiative deactivation pathways and rates of triplet excitons by restricting the vibrational dissipation of long-lived triplets, and considerably increase the possibility of radiative decay. The directed intermolecular halogen bonding can also promote the intersystem-crossing processes by enhancing spin-orbit coupling, and improve the radiative decay. In most studies, various methods are combined to obtain phosphorescence materials of long-lived triplet excited states with high quantum yield.

Correction to Fluorescence and Phosphorescence from Higher Excited States of Organic Molecules

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionORIGINAL ARTICLEThis notice is a correctionCorrection to Fluorescence and Phosphorescence from Higher Excited States of Organic MoleculesTakao ItohCite this: Chem. Rev. 2014, 114, 11, 6080Publication Date (Web):May 22, 2014Publication History Published online22 May 2014Published inissue 11 June 2014https://doi.org/10.1021/cr5002194Copyright © 2014 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views2010Altmetric-Citations1LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (103 KB) Get e-Alerts Get e-Alerts

Similarity transformed equation of motion coupled cluster theory revisited: a benchmark study of valence excited states

The similarity transformed equation of motion coupled cluster (STEOM-CC) method is benchmarked against CC3 and EOM-CCSDT-3 for a large test set of valence excited states of organic molecules studied by Schreiber et al. [M. Schreiber, M.R. Silva-Junior, S.P. Sauer, and W. Thiel, J. Chem. Phys. 128, 134110 (2008)]. STEOM-CC is found to behave quite satisfactorily and provides significant improvement over EOM-CCSD, CASPT2 and NEVPT2 for singlet excited states, lowering standard deviations of these methods by almost a factor of 2. Triplet excited states are found to be described less accurately, however. Besides the parent version of STEOM-CC, additional variations are considered. STEOM-D includes a perturbative correction from doubly excited determinants. The novel STEOM-H (ω) approach presents a sophisticated technique to render the STEOM-CC transformed Hamiltonian hermitian. In STEOM-PT, the expensive CCSD step is replaced by many-body second-order perturbation theory (MBPT(2)), while extended STEOM (EXT-STEOM) provides access to doubly excited states. To study orbital invariance in STEOM, we investigate orbital rotation in the STEOM-ORB approach. Comparison of theses variations of STEOM for the large test set provides a comprehensive statistical basis to gauge the usefulness of these approaches.

Fluorescence and Phosphorescence from Higher Excited States of Organic Molecules

Fluorescence and Phosphorescence from Higher Excited States of Organic Molecules

Howard E. Zimmerman (1926-2012)

Howard E. Zimmerman (1926-2012)

Theoretical methods of investigation of excited states of organic molecules

A brief review of quantum-chemical methods applied to describe excited states of organic molecules is presented. The main emphasis is put on advantages and disadvantages of widely used computational techniques. A brief summary of the performance of such methods and practical recommendations on their use is included.

Molecular orbital modeling of solvent effects on excited states of organic molecules

The excited states of organic molecules are considerably affected in most cases by their environment. A simple example of this phenomenon is the blue-shift effect shown by nπ* bands upon increasing the polarity of the solvent. The purpose of the current paper is to simulate the solvent effect on the excited states of two organic systems: furfural and 1-(N-methyl pyridyl) 2-(p-quinoyl) ethylene (also known as stilbazonium), by creating a set of clusters solute–(solvent) n compounded by distributing solvent molecules around the solute at random. These clusters were subsequently optimized using the semiempirical PM3 method to explore such multiple minima hypersurface of the supermolecular system. The minimal energy sets of each system were selected for the calculation of excited states by the CNDOL method combined with a procedure for singly excited configuration interaction.

Utility of acid-base behavior of excited states of organic molecules

ADVERTISEMENT RETURN TO ISSUEPREVArticleUtility of acid-base behavior of excited states of organic moleculesPeter. Wan and Deepak. ShuklaCite this: Chem. Rev. 1993, 93, 1, 571–584Publication Date (Print):January 1, 1993Publication History Published online1 May 2002Published inissue 1 January 1993https://doi.org/10.1021/cr00017a024RIGHTS & PERMISSIONSArticle Views1228Altmetric-Citations130LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-Alerts Get e-Alerts

A laser-produced plasma as a pulsed source of continuum infrared radiation for time-resolved absorption spectroscopy

Abstract : The focussed beam from the 20 ns pulse of an amplified Nd glass laser produces a high temperature plasma in air or other media. Such plasmas, while well known as phenomena, seem not to have been investigated as a source of infrared radiation. We find the emission in the chemical infrared region, 2100-1700/CM, to be a continuum or white, and at least twenty five times more intense than that from a typical glow bar used in conventional infrared absorption spectroscopy. Emission from the plasma formed in air decays with a wavelength dependent lifetime, about 150 ns for the visible portion, and 2 microsecond for the infrared portion. When formed in argon, the plasma emission is more intense, and the decay time of the infrared emission rises to 4 microsec. Use of this source is demonstrated in a measurement of the carbonyl stretching absorption for W(C0)6 and plans are to apply the method to the determination of infrared absorption spectra of thermally equilibrated excited states of organic molecules and of coordination compounds.

Use of the CNDO method in spectroscopy. XIII. Direct calculation of self-consistent triplet excited states of organic molecules

Use of the CNDO method in spectroscopy. XIII. Direct calculation of self-consistent triplet excited states of organic molecules

MEASUREMENT OF THE TEMPERATURE DEPENDENCE OF THE FLUORESCENCE QUANTUM YIELD OF ORGANIC MOLECULES IN SOLUTION

A DETAILED investigation of the temperature dependence of the fluorescence quantum yield φf can yield–directly or indirectly–significant information about behavior of excited states of organic molecules, such as the temperature effect on radiationless transitions and on photochemical reactivity. Variation of the temperature changes the viscosity of the solvent and, in conjunction with measurements of φf(T), allows investigations of diffusion‐controlled processes. For example, energy transfer and quenching processes as well as excimer or exciplex formation fall into this category. Recent review articles by Weller (1962) and Birks (1970) deal with this topic. Moreover, Huber and Mantulin (1972) have suggested that restraints placed upon geometric modifications of the excited molecule by temperature‐induced changes in the solvent cage (variation of site structure) are reflected in a varying φf.The purpose of this note is to describe and verify a simple procedure, accurate to about ± 5%, for measuring the relative fluorescence quantum yield as a function of temperature. A quantum yield study of 9,10‐diphenylanthracene between room temperature and 77°K is employed to demonstrate the capabilities of this method. In addition, we consider an example of diffusion‐controlled quenching by oxygen measured over a wide temperature range.