Distinguishing yy‐G tautomers by their spectroscopic signatures: A theoretical investigation

A comprehensive theoretical study of electronic transitions of naphtho‐homologated yyG and its five possible tautomers (yyG‐AO7, yyG‐AEc, yyG‐AEt, yyG‐IcO17, and yyG‐ItO17) was performed. The nature of the low‐lying excited states is discussed, and the results are compared to that of y‐bases. Geometry optimizations were performed on the lowest excited singlet ππ* states. Finally, the effects of methanol solution and hydrogen bonding with cytosine on the absorption and emission spectra were examined. The ground state structures were optimized using both the DFT and ab initio HF methods, whereas the excited‐state structures were optimized using the CIS method. The methanol solution was found to red‐shifts both the absorption and emission maxima of the studied bases except for yyG, for which the absorption and emission maxima were blue‐shifted after solvation. In addition, hydrogen bonding with cytosine was found to blue‐shifts both the absorption and emission maxima of yyG, yyG‐AO7, yyG‐IcO17, and yyG‐ItO17. © 2013 Wiley Periodicals, Inc.     

Picosecond Structural Relaxation of Abietic Acid Based Amine End Capped Para‐Phenylenevinylene Trimers in Solution

The synthesis and photophysical properties of six new abietic acid based amine end‐capped p‐phenylenevinylene trimers (AECPV3) in their lowest excited singlet states are presented. The AECPV3 compounds show a large red‐shift of both the absorption (25–30 nm) and emission (37–42 nm) maxima with respect to those of the corresponding trimers. Picosecond time‐resolved fluorescence data reveal the presence of a fast conformational relaxation process (40–62 ps) of the initially excited compounds, leading to more planar conformers. The conformational relaxation time is proportional to the volume of both the side chain and the amine groups.     

Evidence for Two‐Photon Absorption‐Induced ESIPT of Chromophores Containing Hydroxyl and Imino Groups

This paper presents experimental and theoretical investigations into excited‐state intramolecular proton transfer (ESIPT) in new chromophores with hydroxyl and imino groups under one‐ and two‐photon excitation. The results show that internal hydrogen bonding exhibits a remarkable influence on the maximum absorption wavelength of 2‐[(4′‐N,N‐diethylaminodiphenylethylene‐4‐ylimino)methyl]phenol ( C1 ) and 2‐[(4′‐methoxyl‐diphenylethylene‐4‐ylimino)methyl]phenol ( C3 ). Compounds C1 and C3 exhibit well‐separated dual fluorescence emission bands under one‐ and two‐photon excitation. The second fluorescence peaks of C1 and C3 are characterized by much larger Stokes shift than the first normal peaks (ca. 140 vs. 30 nm). 4‐[(4′‐N,N‐Diethylaminodiphenylethylene‐4‐ylimino)methyl]phenol ( C2 ) and 4‐[(4′‐methoxyldiphenylethylene‐4‐ylimino)methyl]phenol ( C4 ) display single emission bands with small Stokes shifts (ca. 30 nm) in various solvents under one‐ and two‐photon excitation. Furthermore, the first emission maxima of C1 and C3 are almost identical to the maximum fluorescence emission wavelengths of C2 and C4 , respectively. These results show that C1 and C3 can undergo ESIPT via a reasonable six‐membered ring, while there is no ESIPT in C2 and C4 under one‐ and two‐photon excitation. Compounds C1 and C2 have larger two‐photon absorption cross‐sections under various near‐infrared laser frequencies tuned from 700 to 880 nm. Molecular geometry optimization of the phototautomers (enol and keto) was performed to analyze the experimental results. The possibility of using these chromophores for metal ions as chemosensors of was thoroughly investigated. In DMF C3 exhibits excellent sensing responses to Zn²⁺ and Fe³⁺ ions through a greatly increased greatly and a largely reduced emission, respectively. In methanol disappearance of ESIPT emission with added Zn²⁺ ions confirms its existence. The binding constants of C3 with Zn²⁺ and Fe³⁺ ions in DMF are also estimated.     

Synthesis of a Far‐Red Photoactivatable Silicon‐Containing Rhodamine for Super‐Resolution Microscopy

The rhodamine system is a flexible framework for building small‐molecule fluorescent probes. Changing N‐substitution patterns and replacing the xanthene oxygen with a dimethylsilicon moiety can shift the absorption and fluorescence emission maxima of rhodamine dyes to longer wavelengths. Acylation of the rhodamine nitrogen atoms forces the molecule to adopt a nonfluorescent lactone form, providing a convenient method to make fluorogenic compounds. Herein, we take advantage of all of these structural manipulations and describe a novel photoactivatable fluorophore based on a Si‐containing analogue of Q‐rhodamine. This probe is the first example of a “caged” Si‐rhodamine, exhibits higher photon counts compared to established localization microscopy dyes, and is sufficiently red‐shifted to allow multicolor imaging. The dye is a useful label for super‐resolution imaging and constitutes a new scaffold for far‐red fluorogenic molecules.     

Synthesis and light‐emitting properties of carbazole‐based copolymers bearing cyano‐substituted arylenevinylene chromophore

Two arylenevinylene compounds bearing the cyano group at α‐position ( 6 ) and β‐position ( 9 ) from the dialkoxylphenylene unit were synthesized, in which the molecular termini were functionalized with 3‐bromocarbazole. The Suzuki coupling copolymerization of these compounds with 1,4‐bis[(3′‐bromocarbazole‐9′‐yl)methylene]‐2,5‐didecyloxybenzene and 9,9‐dihexylfluorene‐2,7‐bis(boronic acid) was carried out to obtain copolymers ( cp67 and cp97 ) containing the cyano‐substituted arylenevinylene fluorophore of 7 mol %. Model compounds ( 6 ′ and 9 ′) corresponding to the arylenevinylene fluorophore were also prepared. The UV spectra of copolymers resembled that of homopolymer hp with no arylenevinylene segment in both CHCl₃ solution and thin film. The emission maxima of copolymers in CHCl₃ (394 nm) agreed with that of homopolymer indicating that the emission bands originated from the carbazole‐fluorene‐carbazole segment. The emission maximum wavelength of copolymer cp67 in thin film (477 nm) indicated fluorescence from the cyano‐substituted arylenevinylene fluorophore because of the occurrence of fluorescence resonance electron transfer. In contrast, copolymer cp97 showed fluorescence at 528 nm to suggest the formation of a new emissive species such as a charge‐transfer complex (exciplex). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 91–98, 2010     

Supramolecular Host‐Inhibited Excited‐State Proton Transfer and Fluorescence Switching of the Anti‐Cancer Drug,Topotecan

The effect of cucurbit[7]uril (CB[7]) nano‐caging on the photophysical properties, particularly excited‐state proton transfer (ESPT) reaction, of an eminent anti‐cancer drug, topotecan (TPT), is demonstrated through steady‐state and time‐resolved fluorescence measurements. TPT in water (pH 6) exists exclusively as the cationic form (C) in the ground state. However, the drug emission mainly comes from the excited‐state zwitterionic form (Z*) of TPT, and is attributed to water‐assisted ESPT between the 10‐hydroxyl group and water, which leads to the transformation of C* to Z* of TPT. In the presence of CB[7], it is found that selective encapsulation of the C form of TPT results in the formation of a 1:1 inclusion complex (CB[7]:TPT), and the ESPT process is inhibited by this encapsulation process. As a result, C* becomes the dominant emitting species in the presence of CB[7] rather than Z*, and fluorescence switching takes place from green to blue. Time‐resolved studies also support the existence of CB[7]‐encapsulated cationic species as the major emitting species in the presence of the macrocyclic host. Semi‐empirical quantum chemical calculations are employed to gain insight into the molecular picture of orientation of TPT in the inclusion complex. It is clearly seen from the optimised structure of 1:1 CB[7]:TPT inclusion complex that both 10‐hydroxyl and 9‐dimethylaminomethylene groups of TPT lie partly inside the cavity, and thereby inhibit the excited‐state transformation of C* to Z* by the ESPT process. Finally, controlled release of the drug is achieved by means of fluorescence switching by introducing NaCl, which is rich in cells, as an external stimulus.     

Preparation and Characterization of Substituted 3‐Benzothiazol‐2‐Ylcoumarins

A series of substituted 3‐benzothiazolylcoumarins was prepared from condensation of 2‐hydroxy‐benzaldehyde and 2‐cyanomethylbenzothiazole to investigate the effect of the nature and position of substituents on their absorption and fluorescent behavior. Compounds with a substituent containing a heteroatom which attached at the C6 position showed a split broad absorption band. Solutions of these compounds in various solvents exhibited brilliant blue fluorescence. The emission intensity for compounds with an alkoxy group at the C6 or C7 position in DMF was approximately 7‐ and 15‐fold higher than for the corresponding precursor and quinine sulfate solution, respectively. These compounds also exhibit high thermal stability in solid state.     

Electronic structure and molecular orbital study of the first excited state of the high‐efficiency blue OLED material bis(2‐methyl‐8‐quinolinolato)aluminum(III) hydroxide complex from ab initio and TD‐B3LYP

Bis(2‐methyl‐8‐quinolinolato)aluminum(III) hydroxide complex (AlMq₂OH) is used in organic light‐emitting diodes (OLEDs) as an electron transport material and emitting layer. By means of ab initio Hartree–Fock (HF) and density functional theory (DFT) B3LYP methods, the structure of AlMq₂OH was optimized. The frontier molecular orbital characteristics and energy levels of AlMq₂OH have been analyzed systematically to study the electronic transition mechanism in AlMq₂OH. For comparison and calibration, bis(8‐quinolinolato)aluminum(III) hydroxide complex (Alq₂OH) has also been examined with these methods using the same basis sets. The lowest singlet excited state (S₁) of AlMq₂OH has been studied by the singles configuration interaction (CIS) method and time‐dependent DFT (TD‐DFT) using a hybrid functional, B3‐LYP, and the 6‐31G* basis set. The lowest singlet electronic transition (S₀ → S₁) of AlMq₂OH is π → π* electronic transitions and primarily localized on the different quinolate ligands. The emission of AlMq₂OH is due to the electron transitions from a phenoxide donor to a pyridyl acceptor from another quinolate ligand including C → C and O → N transference. Two possible electron transfer pathways are presented, one by carbon, oxygen, and nitrogen atoms and the other via metal cation Al³⁺. The comparison between the CIS‐optimized excited‐state structure with the HF ground‐state structure indicates that the geometric shift is mainly confined to the one quinolate and these changes can be easily understood in terms of the nodal patterns of the highest occupied and lowest unoccupied molecular orbitals. On the basis of the CIS‐optimized structure of the excited state, TD‐B3‐LYP calculations predict an emission wavelength of 499.78 nm. An absorption wavelength at 380.79 nm on the optimized structure of B3LYP/6‐31G* was predicted. They are comparable to AlMq2OH 485 and 390 nm observed experimentally for photoluminescence and UV‐vis absorption spectra of AlMq₂OH solid thin film on quartz, respectively. Lending theoretical corroboration to recent experimental observations and supposition, the reasons for the blue‐shift of AlMq2OH were revealed. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

Excited State Intramolecular Proton Transfer of New Diphenylethylene Derivatives Bearing Imino Group: A Combination of Experimental and Theoretical Investigation

In this paper, we described the synthesis and characterization of new diphenylethylene bearing imino group. We concentrated particularly on the investigation of the possibility of the excited state intramolecular charge transfer (ESIPT) of the new dyes experimentally and theoretically. The absorption and fluorescence spectroscopy of the dyes were determined in various solvents. The results showed that the maximal absorption wavelength of 2‐[(4′‐N,N‐dimethylamino‐diphenylethylene‐4‐ylimino)methyl]phenol ( C1 ) and 4‐[(4′‐N,N‐dimethylamino‐diphenylethylene‐4‐ylimino)methyl]phenol ( C2 ) exhibited almost independence on the solvent polarity. While as contrast, the maximal fluorescence wavelength of the dyes showed somewhat dependence on the solvent polarity. In particular, C1 displayed well‐separated dual fluorescence spectroscopy. The second fluorescence peak was characterized with an "abnormal" fluorescence emission wavelength in aprotic solvents with large Stokes shift (ca. 140 nm in THF), which was much more than normal Stokes shift (ca. 30 nm in THF). This emission spectroscopy could be assigned to ESIPT emission. On the other hand, the ESIPT fluorescence of C1 was much reduced or lost in the protic solvents. While, only normal fluorescence emission was detected in various solvents. Although the absorption maxima of C1 exhibited about 10 nm red‐shift with respect to those of C2 , the normal fluorescence maxima of C1 and C2 were almost identical in various solvents. These results suggested that C1 could undergo ESIPT, but C2 was not able to proceed ESIPT. The molecular geometry optimization of phototautomers in the ground electronic state (S₀) was carried out with HF method (Hartree‐Fock) and at DFT level (Density Functional Theory) using B3LYP both, while the CIS was employed to optimize the geometries of the first singlet excited state (S₁) of the phototautomers of C1 and C2 respectively. The properties of the ground state and the excited state of the phototautomers of C1 and C2 , including the geometrical parameter, the energy, the frontier orbits, the Mulliken charge and the dipole moment change were performed and compared completely. The data were analyzed further based on our experimental results. Furthermore, the absorption and fluorescence spectra were calculated in theory and compared with the measured ones. The rate constant of internal proton transfer (9.831×10¹¹ s^?1) of C1 was much lower than that of salicylidene methylamine ( C3 , 2.045×10¹⁵ s^?1), which was a typical Schiff base compound and was well demonstrated to undergo ESIPT easily under photoexcitation.     

Absorption Spectrum of A–T DNA Unraveled by Quantum Mechanical Calculations in Solution on the (dA)2⋅(dT)2 Tetramer

The absorption spectrum of A–T DNA is computed for the first time in aqueous solution by means of quantum mechanical calculations performed on realistic models, thereby accounting for both stacking and base pairing interactions and including solvent effects through the polarizable continuum model. The computed and experimental spectra are in close agreement. Our analysis allows the identification of all the electronic transitions hidden in the broad absorption spectrum of A–T DNA, thus determining their most relevant properties and providing an explanation for the most significant experimental features, such as the small blue shift of the band maximum and the appearance of a shoulder on the red wing of the absorption band. The lowest‐energy dark excited state corresponds to a charge‐transfer state between two stacked adenine bases.     

High‐Energy Long‐Lived Mixed Frenkel–Charge‐Transfer Excitons: From Double Stranded (AT)n to Natural DNA

The electronic excited states populated upon absorption of UV photons by DNA are extensively studied in relation to the UV‐induced damage to the genetic code. Here, we report a new unexpected relaxation pathway in adenine–thymine double‐stranded structures (AT)_n. Fluorescence measurements on (AT)_n hairpins (six and ten base pairs) and duplexes (20 and 2000 base pairs) reveal the existence of an emission band peaking at approximately 320 nm and decaying on the nanosecond time scale. Time‐dependent (TD)‐DFT calculations, performed for two base pairs and exploring various relaxation pathways, allow the assignment of this emission band to excited states resulting from mixing between Frenkel excitons and adenine‐to‐thymine charge‐transfer states. Emission from such high‐energy long‐lived mixed (HELM) states is in agreement with their fluorescence anisotropy (0.03), which is lower than that expected for π–π* states (≥0.1). An increase in the size of the system quenches π–π* fluorescence while enhancing HELM fluorescence. The latter process varies linearly with the hypochromism of the absorption spectra, both depending on the coupling between π–π* and charge‐transfer states. Subsequently, we identify the common features between the HELM states of (AT)_n structures with those reported previously for alternating (GC)_n: high emission energy, low fluorescence anisotropy, nanosecond lifetimes, and sensitivity to conformational disorder. These features are also detected for calf thymus DNA in which HELM states could evolve toward reactive π–π* states, giving rise to delayed fluorescence.     

Fluorene‐Based π‐Conjugated Oligomers for Efficient Three‐Photon Excited Photoluminescence and Lasing

A novel series of diphenylamino‐ and 1,2,4‐triazole‐end‐capped, fluorene‐based, π‐conjugated oligomers that includes extended oligofluorenes and oligothienylfluorenes has been synthesized by means of the palladium‐catalyzed Suzuki cross‐coupling of 9,9‐dibutyl‐7‐(diphenylamino)‐2‐fluorenylboronic acid and the corresponding 1,2,4,‐triazole‐based aryl halide as a key step. It was demonstrated that efficient two‐ and three‐photon excited photoluminescence and lasing in the blue region are obtained by pumping near‐infrared femtosecond lasers on these materials. Although the absorption and emission maxima of the highly fluorescent and extended oligofluorenes reach a saturation limit, there exists an effective conjugation length for an optimum three‐photon absorption cross section in the homologous oligofluorene series. On the other hand, the multiphoton excited emission spectrum and lasing wavelength can easily be modified or tuned by an incorporation of thienyl unit(s) into the fluorene‐based π‐conjugated core with which exceptionally large three‐photon absorption cross sections up to 3.59×10^?77 cm⁶ s² in the femtosecond regime have been obtained, thereby highlighting the potential of this series of photonic materials. The optimized full width at half‐maximum of the cavityless three‐photon upconverted blue lasing spectra are sharply narrowed to approximately 6 nm with an efficiency of up to 0.013 %.     

Photophysical properties of the isomorphic emissive RNA nucleobase analogues and effect of water solution,ribose, and base pairing: A theoretical study

In the present work, a comprehensive theoretical investigation on the excited state properties of the isomorphic emissive RNA nucleobase analogues, namely ^tzA, ^tzG, ^tzC, and ^tzU, was performed. Vertical transition energies are determined with the time‐dependent density functional theory method at both the B3LYP and CAM‐B3LYP levels using the 6‐311++G(d,p) basis set. The nature of the low‐lying singlet excited states is discussed and the results are compared with the findings from experiment and those for thieno analogues and natural bases. In gas phase, it was found that the S₁ state is ππ* in nature for all the tz‐bases except for ^tzA, for which the S₁ state is predicted to be nπ* in nature with the ππ* state being the S₂. While in water solution, the S₁ state for all tz‐bases are predicted to be ππ* dominated by the configuration HOMO→LUMO. Compared with natural bases, the lowest ππ* states are about 0.85–1.22 eV red‐shifted. When compared with thieno analogues, it is interesting to note that the S₁ state (ππ*) transition energies of the two counterparts from the two alphabets are nearly equal due to the very little differences of their HOMO‐LUMO gaps. In addition, it was found that the hydration + PCM model can perfectly reproduce the photophysical properties of the tz‐bases since the calculated excitation maxima and fluorescence are in good agreement with the experimental data. The microenvironment effects of linking to ribose, base pairing, and further hydration of base pairs were also studied.     

Density functional study on the effect of substituent group for the monomer of donor‐acceptor copolymer

The effect of the substituent groups (alkyl or aryl) on the structure, electronic, optical properties, ionization potentials (IPs), electron affinities (EAs), and reorganization energy of the donor–acceptor monomers 5,8‐di‐2‐thienyl‐quinoxaline (T[Q]T), 4,9‐di‐2‐thienylpyrazine[2,3‐g]quinoxaline (T[PQ]T) were studied theoretically. The lowest‐lying absorption in assigned to π→π* transition, and the fluorescence can be described as originating from the ¹[ππ*] excited state. The lowest‐lying absorption and emission spectrum of T[Q]T and T[PQ]T with alkyl groups exhibit blue‐shifted, while T[Q]T and T[PQ]T with aryl groups exhibit the opposite result. The extra absorption bond at 400 nm of T[Q]T‐Bph is contributed by the π‐π* transitions between the biphenyl and acceptor fragment. Orbital compositions transfer coefficient (χ) of the donor in LUMOs is reduced with the aryl groups on the acceptor, which illuminates that the aryl contributes to intramolecular charge transfer, and the result is in accord with the analysis of reorganization energy. IPs is brought down by both of the alkyl and aryl groups, but EAs is raised only by aryl, therefore, aryl is conductive to forming excitons for D‐A‐D molecule. Consequently, T[Q]T and T[PQ]T with aryl groups are more reasonable monomers of donor–acceptor copolymers as a solar cell materials comparing with the alkyl‐introduced ones. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Efficient White‐Light Generation from Ionically Self‐Assembled Triply‐Fluorescent Organic Nanoparticles

Low cost, simple, and environmentally friendly strategies for white‐light generation which do not require rare‐earth phosphors or other toxic or elementally scare species remain an essentially unmet challenge. Progress in the area of all‐organic approaches is highly sought, single molecular systems remaining a particular challenge. Taking inspiration from the designer nature of ionic‐liquid chemistry, we now introduce a new strategy toward white‐light emission based on the facile generation of nanoparticles comprising three different fluorophores assembled in a well‐defined stoichiometry purely through electrostatic interactions. The building blocks consist of the fluorophores aminopyrene, fluorescein, and rhodamine 6G which represent blue, green, and red‐emitting species, respectively. Spherical nanoparticles 16(±5) nm in size were prepared which display bright white‐light emission with high fluorescence quantum efficiency (26 %) and color coordinate at (0.29, 0.38) which lie in close proximity to pure white light (0.33, 0.33). It is noteworthy that this same fluorophore mixture in free solution yields only blue emission. Density functional theory calculations reveal H‐bond and ground‐state proton transfer mediated absolute non‐parallel orientation of the constituent units which result in frustrated energy transfer, giving rise to emission from the individual centers and concomitant white‐light emission.     

Multicolored‐Fluorescence Switching of ICT‐Type Organic Solids with Clear Color Difference: Mechanically Controlled Excited State

A donor–acceptor‐type fluorophore containing a twisted diphenylacrylonitrile and triphenylamine has been developed by using the Suzuki reaction. The system indicates typical intramolecular charge‐transfer properties. Upon mechanical grinding or hydrostatic pressure, the fluorophore reveals a multicolored fluorescence switching. Interestingly, a fluorescence color transition from green to red was clearly observed, and the change of photoluminescent (PL) wavelength gets close to 111 nm. The mechanisms of high‐contrast mechanochromic behavior are fully investigated by techniques including powder XRD, PL lifetime, high‐pressure PL lifetime, and Raman spectra analysis. The tremendous PL wavelength shift is attributed to gradual transition of excited states from the local excited state to the charge‐transfer state.     

Synthesis,Structural Characterization,Photophysics, and Broadband Nonlinear Absorption of a Platinum(II) Complex with the 6‐(7‐Benzothiazol‐2′‐yl‐9,9‐diethyl‐9 H‐fluoren‐2‐yl)‐2,2′‐bipyridinyl Ligand

A platinum complex with the 6‐(7‐benzothiazol‐2′‐yl‐9,9‐diethyl‐9H‐fluoren‐2‐yl)‐2,2′‐bipyridinyl ligand ( 1 ) was synthesized and the crystal structure was determined. UV/Vis absorption, emission, and transient difference absorption of 1 were systematically investigated. DFT calculations were carried out on 1 to characterize the electronic ground state and aid in the understanding of the nature of low‐lying excited electronic states. Complex 1 exhibits intense structured ¹π–π* absorption at λ_abs<440 nm, and a broad, moderate ¹M LCT/¹LLCT transition at 440–520 nm in CH₂Cl₂ solution. A structured ³π–π*/³M LCT emission at about 590 nm was observed at room temperature and at 77 K. Complex 1 exhibits both singlet and triplet excited‐state absorption from 450 nm to 750 nm, which are tentatively attributed to the ¹π–π* and ³π–π* excited states of the 6‐(7‐benzothiazol‐2′‐yl‐9,9‐diethyl‐9H‐fluoren‐2‐yl)‐2,2′‐bipyridine ligand, respectively. Z‐scan experiments were conducted by using ns and ps pulses at 532 nm, and ps pulses at a variety of visible and near‐IR wavelengths. The experimental data were fitted by a five‐level model by using the excited‐state parameters obtained from the photophysical study to deduce the effective singlet and triplet excited‐state absorption cross sections in the visible spectral region and the effective two‐photon absorption cross sections in the near‐IR region. Our results demonstrate that 1 possesses large ratios of excited‐state absorption cross sections relative to that of the ground‐state in the visible spectral region; this results in a remarkable degree of reverse saturable absorption from 1 in CH₂Cl₂ solution illuminated by ns laser pulses at 532 nm. The two‐photon absorption cross sections in the near‐IR region for 1 are among the largest values reported for platinum complexes. Therefore, 1 is an excellent, broadband, nonlinear absorbing material that exhibits strong reverse saturable absorption in the visible spectral region and large two‐photon‐assisted excited‐state absorption in the near‐IR region.     

Concise Synthesis and Two‐Photon‐Excited Deep‐Blue Emission of 1,8‐Diazapyrenes

Efficient violet–blue‐emitting molecules are especially useful for applications in full‐color displays, solid‐state lighting, as well as in two‐photon absorption (TPA) excited frequency‐upconverted violet–blue lasing. However, the reported violet–blue‐emitting molecules generally possess small TPA cross sections. In this work, new 1,8‐diazapyrenes derivatives 3 with blue two‐photon‐excited fluorescence emission were concisely synthesized by the coupling reaction of readily available 1,4‐naphthoquinone O,O‐diacetyl dioxime ( 1 ) with internal alkynes 2 under the [{RhCl₂Cp*}₂]–Cu(OAc)₂ (Cp*=pentamethylcyclopentadienyl ligand) bimetallic catalytic system. Elongation of the π‐conjugated length of 1,8‐diazapyrenes 3 led to the increase of TPA cross sections without the expense of a redshift of the emission wavelength, probably due to the rigid planar structure of chromophores. It is especially noteworthy that 2,3,6,7‐tetra(4‐bromophenyl)‐1,8‐diazapyrene ( 3c ) has a larger TPA cross section than those of other molecules reported so far. These experimental results are explained in terms of the effects of extension of the π‐conjugated system, intramolecular charge transfer, and reduced detuning energy.     

4‐Trifluoromethyl‐Substituted Coumarins with Large Stokes Shifts: Synthesis,Bioconjugates, and Their Use in Super‐Resolution Fluorescence Microscopy

Bright and photostable fluorescent dyes with large Stokes shifts are widely used as sensors, molecular probes, and light‐emitting markers in chemistry, life sciences, and optical microscopy. In this study, new 7‐dialkylamino‐4‐trifluoromethylcoumarins have been designed for use in bioconjugation reactions and optical microscopy. Their synthesis was based on the Stille reaction of 3‐chloro‐4‐trifluoromethylcoumarins and available (hetero)aryl‐ or (hetero)arylethenyltin derivatives. Alternatively, the acylation of 2‐trifluoroacetyl‐5‐dialkylaminophenols with available (hetero)aryl‐ or (hetero)arylethenylacetic acids followed by intramolecular condensation afforded coumarins with 3‐(hetero)aryl or 3‐[2‐(hetero)aryl]ethenyl groups. Hydrophilic properties were provided by the introduction of a sulfonic acid residue or by phosphorylation of a primary hydroxy group attached at C‐4 of the 2,2,4‐trimethyl‐1,2‐dihydroquinoline fragment fused to the coumarin fluorophore. For use in immunolabeling procedures, the dyes were decorated with an (activated) carboxy group. The positions of the absorption and emission maxima vary in the ranges 413–480 and 527–668 nm, respectively. The phosphorylated dye, 9 ,CH?CH‐2‐py,H, with the 1‐(3‐carboxypropyl)‐4‐hydroxymethyl‐2,2‐dimethyl‐1,2‐dihydroquinoline fragment fused to the coumarin fluorophore bearing the 3‐[2‐(2‐pyridyl)ethenyl] residue (absorption and emission maxima at 472 and 623 nm, respectively) was used in super‐resolution light microscopy with stimulated emission depletion and provided an optical resolution better than 70 nm with a low background signal. As a result of their large Stokes shifts, good fluorescence quantum yields, and adequate photostabilities, phosphorylated coumarins enable two‐color imaging (using several excitation sources and a single depletion laser) to be combined with subdiffractional optical resolution.     

Deep‐red emissive conjugated poly(2,6‐BODIPY‐ethynylene)s bearing alkyl side chains

Novel deep‐red emissive poly(2,6‐BODIPY‐ethynylene)s bearing dodecyl side chains (polymers A , B , and C ) have been prepared by palladium‐catalyzed Sonogashira polymerization of 2,6‐diiodo‐functionalized BODIPY monomers with 2,6‐diethynyl‐functionalized BODIPY monomers. These polymers emit in the deep‐red region with emission maxima at up to 690 nm, and exhibit significant red shifts (up to 166 and 179 nm) of both absorption and emission maxima compared with their parent BODIPY dyes due to significant extension of π‐conjugation. These polymers possess good thermal stability with decomposition temperature between 270 and 360 °C. The polymers exhibit a little larger Stokes shifts and shorter lifetime than their corresponding BODIPY dyes. The solid state thin films of polymers A , B , and C emit in near‐infrared region between 723 and 743 nm, and show significantly red shifts (up to 57 nm) in absorption and emission maxima relative to their polymer solution. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5354–5366, 2009