Femtosecond Spectroscopy of Superfluorescent Fluorenyl

Article pubs.acs.org/JPCC

Femtosecond Spectroscopy of Superfluorescent Fluorenyl Benzothiadiazoles with Large Two-Photon and Excited-State Absorption Kevin D. Belfield,*,†,‡ Mykhailo V. Bondar,§ Sheng Yao,† Ivan A. Mikhailov,∥ Vyacheslav S. Polikanov,∥ and Olga V. Przhonska§ †

Department of Chemistry and ‡CREOL, College of Optics and Photonics, University of Central Florida, P.O. Box 162366, Orlando, Florida 32816-2366, United States § Institute of Physics, Prospect Nauki 46, Kiev-28, 03028, Ukraine ∥ Petersburg Nuclear Physics Institute, 188300, St. Petersburg, Russia ABSTRACT: New symmetrical fluorene-containing derivatives with a benzothiadiazole (BTD) central core, 4,7-bis(5-(9,9-didecyl-7(phenylsulfonyl)-9H-fluoren-2-yl)thiophen-2-yl)benzo[c][1,2,5]thiadiazole (1) and 4,7-bis(5′-(9,9-didecyl-7-(phenylsulfonyl)-9Hfluoren-2-yl)-2,2′-bithiophen-5-yl)benzo[c][1,2,5]thiadiazole (2), were prepared, and multifarious linear photophysical and nonlinear optical properties, potentially attractive for a number of emerging applications, were investigated. Comprehensive photophysical and photochemical characterization was performed in a number of organic solvents at room temperature, including linear, one-photon absorption (1PA), steady-state fluorescence, excitation anisotropy, and fluorescence lifetime properties. Fast relaxation processes in the excited states of 1 and 2 with characteristic times of ∼0.2−3 ps were revealed by a femtosecond transient absorption pump−probe method. Large two-photon absorption (2PA) cross sections of 1 and 2 (up to 2500−2700 GM) were obtained by an open aperture Z-scan technique. Efficient two-photon optical power limiting (OPL) behavior with a figure of merit (FOM) ≈ 15.4 and superfluorescence properties were demonstrated in solution under femtosecond excitation. The electronic structure and optical parameters of 1 and 2 were analyzed by quantum chemical calculations using the TD-DFT method. Simulated linear absorption spectra were found in good agreement with experimental data while 2PA cross sections were overestimated via computational simultation and a possible explanation is provided. Good fluorescence quantum yields, long wavelength absorption, far-red to near-IR emission, efficient OPL and superfluorescence properties, large 2PA cross sections, and extremely high photochemical stability make these new materials good candidates for emerging nonlinear optical applications, including optical sensor protection, stimulated emission depletion microscopy, and two-photon fluorescence microscopy deep tissue bioimaging. transfer,30−32 relaxation rates and deactivation pathways of excited states in solvents of different polarities,15,33−38 chargetransfer kinetics in metal−organic complexes and lightharvesting biological systems,39,40 and solvation dynamics41,42 have been investigated for a number of organic compounds using a well-defined transient absorption pump−probe method.43,44 Benzothiadiazole (BTD) derivatives with large 2PA cross sections are promising candidates for most of the applications mentioned above45,46 as well as fluorescence chemosensor technology47 and photovoltaic devices.48−51 Certain linear spectroscopic and nonlinear optical properties of BTD-based compounds have been reported (see, e.g., refs 45,46,49,51−54)

1. INTRODUCTION The development of new organic molecules with efficient twophoton absorption (2PA) and specific linear photophysical and nonlinear optical properties remains a subject of great interest for a wide range of emerging applications, including twophoton fluorescence bioimaging,1−4 optical power limiting,5−8 microfabrication and optical data storage,9−11 and singlet oxygen-based photodynamic therapy.12−14 The nature of molecular electronic structure and fast inter- and intramolecular dynamic processes plays an important role in the formation of particular linear and nonlinear optical properties, such as transient excited-state absorption (ESA),15−17 stimulated emission depletion (STED),18−20 and superfluorescence and lasing abilities,21−23 which are of great fundamental interest and need to be clearly determined. Fast dynamic processes of photochemical reactions,24−27 formation of triplet−triplet ESA and triplet−triplet annihilation,28,29 intramolecular hydrogen © XXXX American Chemical Society

Received: March 28, 2014 Revised: May 16, 2014

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dx.doi.org/10.1021/jp503106k | J. Phys. Chem. C XXXX, XXX, XXX−XXX

The Journal of Physical Chemistry C

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Figure 1. Molecular structures of 1 and 2.

room temperature.59 The fluorescence quantum yields of 1 and 2, Φfl, were obtained by a standard method58 relative to Rhodamine 6G in ethanol.60 Fluorescence lifetimes, τfl, were measured with a PicoQuant PicoHarp 300 time-correlated single photon-counting system with time resolution ≈80 ps, using femtosecond excitation (MIRA-900, Coherent Inc.), linearly polarized at the magic angle. Photochemical decomposition quantum yields of 1 and 2, Φph, were determined in air-saturated solutions at room temperature under CW diode laser irradiation (excitation wavelength λex ≈ 532 nm, average intensity ≈120 mW/cm2) by the absorption method described previously.61 2.3. 2PA, Optical Power Limiting, Superfluorescence, and Transient Absorption Measurements. Nonlinear optical and transient absorption measurements were performed with a 1 kHz femtosecond laser system with two OPAs (all lasers from Coherent, Inc.), previously described in detail.59,62 Briefly, the output of the femtosecond self-mode-locking Ti:sapphire laser (Mira 900-F), tuned to 800 nm, was regeneratively amplified by a Legend Elite (USP) system, providing a laser beam with 1 kHz repetition rate, pulse duration τP ≈ 100 fs, and pulse energy EP ≈ 4 mJ. The amplified laser output was divided into two equal parts that separately pumped two OPAs (Opera Solo) with a broad tuning range, 0.24−20 μm, EP ≤ 200 μJ, and τP ≈ 100 fs. A single laser beam from one OPA was used for 2PA cross section measurements with an open-aperture Z-scan method63 and for the investigation of two-photon optical power limiting behavior.7 Superfluorescence properties of 1 and 2 were studied under one-photon femtosecond transverse pumping using a cylindrical lens and spectrofluorometric quartz cuvettes 4 × 10 × 35 mm. Superfluorescence emission was registered perpendicular to the pumping beam with a fiber-optic spectrometer HR4000 (Ocean Optics, Inc.). Transient absorption measurements were performed employing a welldefined pump−probe technique43,59 with two linearly polarized laser beams from separate OPAs, using optical delay line M531.DD (PI, Inc.), as reported previously.64 All measurements were conducted in a 1 mm path length quartz flow cell in order to prevent possible photochemical and thermooptical distortions. 2.4. Quantum-Chemical Calculations. To analyze the electronic properties of 1 and 2, quantum-chemical calculations were performed with the Gaussian’09, Rev. A2 suite of programs.65 Aliphatic side chains (C10H21) in 1 and 2, in the fluorenyl 9-positions, do not belong to the π-system and were replaced with methyl groups for computational efficiency. The resulting structures were denoted 1a and 2a. We used TDDFT//DFT with the CAM-B3LYP66//B3LYP67 functionals in the excitation and optimization simulations, respectively, and

using conventional steady-state spectroscopic techniques, while a general strategy for the development of narrow-bandgap organic materials has been established.45,49,55 Much less attention has been paid to the investigation of the fast kinetic processes that occur in the ground and excited electronic states of BTD derivatives.56,57 In this paper we present comprehensive linear steady-state, time-resolved, and nonlinear optical spectral investigations of two intriguing BTD derivatives, 4,7bis(5-(9,9-didecyl-7-(phenylsulfonyl)-9H-fluoren-2-yl)thiophen-2yl)benzo[c][1,2,5]thiadiazole (1) and 4,7-bis(5′(9,9-didecyl-7-(phenylsulfonyl)-9H-fluoren-2-yl)-2,2′-bithiophen-5-yl)benzo[c][1,2,5]thiadiazole (2), with the electronacceptor BTD central core and electron-donating fluorenylthiophene units separated by different π-conjugated spacers. The nature of the fast relaxation processes in the excited states along with efficient 2PA, two-photon optical power limiting (OPL), and superfluorescent properties of 1 and 2 are reported. The novel compounds (1 and 2) were also investigated theoretically: density functional theory (DFT) was used for geometry optimization, while time-dependent DFT (TD-DFT) was used for simulation of excited states. A unique combination of several nonlinear optical properties of 1 and 2 makes them attractive for a number of important technological applications, including two-photon fluorescence microscopy (2PFM).

2. EXPERIMENTAL SECTION 2.1. Materials. The molecular structures of new fluorene containing symmetrical BTD derivatives 1 and 2 are shown in Figure 1 (synthesis will be described elsewhere). The chemical structure and purity of the new compounds was confirmed by 1 H and 13C NMR spectroscopy and high-resolution mass spectroscopy (HRMS). All solvents were of spectroscopic grade and used without further purification. 2.2. Linear Photophysical and Photochemical Characterization. The steady-state linear spectral properties, fluorescence lifetimes, and photochemical stabilities of 1 and 2 were investigated in air saturated toluene (TOL), tetrahydrofuran (THF), and dichloromethane (DCM) at room temperature. One-photon linear absorption (1PA) spectra were obtained using a UV−vis spectrophotometer (Agilent 8453) in 10 mm path length quartz cuvettes and a range of molecular concentrations, C ≈ (2−5) × 10−5 M. The steady-state fluorescence and excitation anisotropy spectra of 1 and 2 were measured with a Quantamaster spectrofluorimeter (PTI, Inc.) in dilute solutions (C ∼ 10−6 M), using 10 mm spectrofluorometric quartz cells. The corresponding correction of the spectral responsivity of the PTI detection system was performed for all fluorescence emission spectra. The values of fundamental excitation anisotropies of the compounds, r(λ),58 were determined in viscous polytetrahydrofuran (pTHF) at B



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Figure 2. Normalized linear absorption (1−3), steady-state fluorescence (1′−3′), and excitation anisotropy (4) spectra of 1 (a) and 2 (b) in TOL (1, 1′), THF (2, 2′), DCM (3, 3′), and pTHF (4).

Table 1. Linear Photophysical and Photochemical Parameters of 1 and 2a 1 λmax ab , nm λmax fl , nm Stokes shift, nm (cm−1) εmax × 10−3, M−1 cm−1 μ01, D Φfl, % τfl,b ns τcal fl , ns Φph × 106

2

TOL

THF

DCM

TOL

THF

DCM

508 ± 1 622 ± 1 114 ± 2 (≈ 3610) 40 ± 2 8.1 67 ± 3 4.0 ± 0.1 3.8 ± 0.7 0.032

510 ± 1 638 ± 1 128 ± 2 (≈ 3930) 43 ± 2 8.6 64 ± 3 4.7 ± 0.1 3.9 ± 0.7 0) gradually decreases and transforms into the gain phenomenon (ΔD < 0), which is in good agreement with the efficient superfluorescence properties of 1 and 2. The kinetic curves for all probe wavelengths λpr obtained under long wavelength pump, S0 → S1 (λpm = 510 nm for 1, and λpm = 530 nm for 2) were sufficiently similar to the corresponding ones observed for short wavelength excitation at λpm = 400 nm. Some small differences in the transient absorption curves, ΔD = f(τD), were observed in the temporal range ≤500−700 fs only for several λpr, and the examples of such differences are shown in Figure 8. According to these results, the observed femtosecond relaxations are completed faster in the case of S0 → S1 excitation relative to those from the corresponding S0 → Sn. It is reasonable to assume that the temporal differences obtained (≈200 fs for 1 (Figure 8a) and ≈400 fs for 2 (Figure 8b)) are determined by the additional time of Sn → S1 nonradiative transition participating in the fast relaxation processes in 1 and 2 after S0 → Sn excitation. This means that characteristic times of Sn → S1 vibronic transitions did not exceed ≈200 fs and ≈400 fs for 1 and 2, respectively, and are comparable with corresponding values of typical laser dyes.90,91 It should be emphasized that the temporal differences obtained were detected only for λpr from the spectral range of

relatively sharp changes in the ESA and/or gain contours, where small spectral shifts resulted in large changes in ΔD. 3.6. Quantum Chemical Modeling of the Electronic Properties of 1 and 2. The optimized model structures 1a and 2a (which are 1 and 2 with the aliphatic C10H21 chains replaced by CH3 groups) are shown in Figure 9 from two different perspectives. They are close to the C2 symmetry group, so we refer to symmetry representations A and B (a and b) for states (molecular orbitals). The 1PA and 2PA spectra simulated at the TD-CAM-B3LYP/6-31G* level of theory are shown in Figure 10a for 1a and Figure 10b for 2a. TD-DFT calculations satisfactorily reproduce excitation energies for the first two maxima of the 1PA spectra, although the first (long wavelength) peak should be broadened more than the second one according to the experimental observations (see Figures 2 and 4). This is probably because of vibronic contributions, which we neglected by approximation with the Lorentz shapefunction. The experimental broadening of the first 1PA maximum may also be interpreted as a presence of an extra excited state missed or shifted in the simulations. For instance, the S2 state in our simulation, which comprises the right shoulder of the second peak for 2a (see Figure 10b), may turn out to be blue-shifted by about 100 nm from its real position. Then the corresponding red shift would produce a left shoulder for the first 1PA peak. The TD-CAM-B3LYP calculations satisfactorily reproduce the 2PA spectra for the excitation wavelengths corresponding to the S4 and S2 states (600−700 nm) for 1a and 2a, respectively. However, the longer-wavelength region is misrepresented: the 2PA maximum at about 1000 nm (with a value of ca. 100 GM for 1a and 400 GM for 2a) is completely missing in our simulations. This experimental peak may correspond to the doubly electronically excited state missed at the TD-DFT level of theory. Alternatively, the reason for its absence can be the same as for the broadening of the first 1PA maximum: either a vibronic contribution of the S1 state or a shift in excitation energy of the S2 state. The transition and permanent dipoles calculated for the lowest four excited states of 1a and 2a are listed in Table 2 along with their excitation energies, orbital configurations, and contributions to δ2PA. The X-component of the dipoles, transformed according to the B representation, has the largest value. The second-largest component of the dipoles is Z, which is symmetric in C2. Accordingly, the maximum 1PA probability appears for the states belonging to the B representation. Symmetric states have less, but nonzero, 1PA probability. Similarly, the highest 2PA cross sections are observed for AG



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for by considering vibronic contributions of the first excited state. Good fluorescence quantum yields, long wavelength absorption, far-red to near-IR emission, efficient OPL and superfluorescence properties, large 2PA cross sections, and extremely high photochemical stability make the new BTDbased derivatives good candidates for emerging nonlinear optical applications, including optical sensor protection, STED microscopy, and 2PFM deep tissue bioimaging.

Table 2. Permanent μii ≡ Δμ0i and Transition Dipole Moments μij in Debye Obtained at the TD-CAM-B3LYP/631G* Level of Theory for the Ground (S0) and Excited (Sj) States, that Essentially Contribute to the 2PA of the First Four Excited States of 1a (Top Half of the Table) and 2a (Bottom)a

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AUTHOR INFORMATION

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We wish to acknowledge the National Science Foundation (CHE-0840431 and CHE-0832622), the US National Academy of Sciences (PGA-P210877), and the National Academy of Sciences of Ukraine (Grants 1.4.1.B/153 and VC/157). Calculations were performed using the HPCC facilities of the I2Lab (Interdisciplinary Information Science and Technology Laboratory) at the University of Central Florida.

a St# stands for i and j in the first column and row. Columns X and Z correspond to projections of the dipoles defined in Figure 9. The Yprojection is negligible. The ground state dipole moment has been subtracted from the permanent dipoles. The other columns contain transition energies En = E0j in eV and 2PA cross section δ2PA in GM, obtained at the same level of theory. Orbital configurations (config) of the corresponding transitions with the highest contributions (contrib) are given in the following notations: H and L are the highest occupied and lowest unoccupied molecular orbitals.

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states due to large contributions from μxμx matrix elements, while smaller μxμz matrix elements result in lower 2PA cross sections for B-states (where μx and μz are the X and Z projections of transition dipoles, respectively).

REFERENCES

(1) Nag, O. K.; Lim, C. S.; Nguyen, B. L.; Kim, B.; Jang, J.; Han, J. H.; Cho, B. R.; Woo, H. Y. pH-Responsive Water Soluble Smart Vesicles Containing a Bis(Styryl)Benzene Derivative for Two-Photon Microscopy Imaging. J. Mater. Chem. 2012, 22, 1977−1984. (2) Heo, C. H.; Kim, K. H.; Kim, H. J.; Baik, S. H.; Song, H.; Kim, Y. S.; Lee, J.; Mook-jung, I.; Kim, H. M. A Two-Photon Fluorescent Probe for Amyloid-B Plaques in Living Mice. Chem. Commun. 2013, 49, 1303−1305. (3) Aparicio-Ixta, L.; Ramos-Ortiz, G.; Pichardo-Molina, J. L.; Maldonado, J. L.; Rodŕıguez, M.; Tellez-Lopez, V. M.; MartinezFong, D.; Zolotukhin, M. G.; Fomine, S.; Meneses-Navaa, M. A.; et al. Two-Photon Excited Fluorescence of Silica Nanoparticles Loaded with a Fluorene-Based Monomer and Its Crossconjugated Polymer: Their Application to Cell Imaging. Nanoscale 2012, 4, 7751−7759. (4) Zhang, Y.; Wang, J.; Jia, P.; Yu, X.; Liu, H.; Liu, X.; Zhao, N.; Huang, B. Two-Photon Fluorescence Imaging of DNA in Living Plant Turbid Tissue with Carbazole Dicationic Salt. Org. Biomol. Chem. 2010, 8, 4582−4588. (5) Tang, C.; Zheng, Q.; Zhu, H.; Wang, L.; Chen, S.-C.; Ma, E.; Chen, X. Two-Photon Absorption and Optical Power Limiting Properties of Ladder-Type Tetraphenylene Cored Chromophores with Different Terminal Groups. J. Mater. Chem. C 2013, 1, 1771− 1780. (6) Chateau, D.; Chaput, F.; Lopes, C.; Lindgren, M.; Brännlund, C.; Ö hgren, J.; Djourelov, N.; Nedelec, P.; Desroches, C.; Eliasson, B.; et al. Silica Hybrid Sol−Gel Materials with Unusually High Concentration of Pt−Organic Molecular Guests: Studies of Luminescence and Nonlinear Absorption of Light. ACS Appl. Mater. Interfaces 2012, 4, 2369−2377. (7) Lin, T. C.; He, G. S.; Zheng, Q. D.; Prasad, P. N. Degenerate Two-/Three-Photon Absorption and Optical Power-Limiting Properties in Femtosecond Regime of a Multi-Branched Chromophore. J. Mater. Chem. 2006, 16, 2490−2498. (8) Lin, T.-C.; Lee, Y.-H.; Huang, B.-R.; Hu, C.-L.; Li, Y.-K. TwoPhoton Absorption and Effective Optical Power-Limiting Properties of Small Dendritic Chromophores Derived from Functionalized Fluorene/Oxadiazole Units. Tetrahedron 2012, 68, 4935−4949. (9) Woods, R.; Feldbacher, S.; Langer, G.; Satzinger, V.; Schmidt, V.; Kern, W. Epoxy Silicone Based Matrix Materials for Two-Photon Patterning of Optical Waveguides. Polymer 2011, 52, 3031−3037. (10) Belfield, K. D.; Ren, X.; Hagan, D. J.; Van Stryland, E. W.; Dubikovsky, V.; Miesak, E. J. Near-IR Two-Photon Photoinitiated

4. CONCLUSIONS Comprehensive linear photophysical and photochemical characterization, nonlinear optical properties, and femtosecond transient absorption spectroscopy of new BTD-based materials 1 and 2 was conducted. The steady-state linear spectral properties and fluorescence lifetimes of 1 and 2 revealed a specific charge-transfer character of the first excited electronic state S1, resulting in a large Stokes shift (∼3600−4200 cm−1), weak solvatochromic behavior, and strong dependence of τfl on solvent polarity (for 2). The extremely high photochemical stability of 1 and 2 (with corresponding photochemical decomposition quantum yields Φph ∼ 10−7−10−8) was demonstrated under CW laser irradiation in a number of organic solvents at room temperature. Degenerate 2PA spectra of 1 and 2 were obtained over a broad spectral range revealing maximum 2PA cross sections of ∼2500−2700 GM with no perceptible dependence on solvent polarity, properties that make these new materials particularly attractive for use in a number of 2PA-based applications. Efficient two-photon OPL (with FOM ≈ 15.4) and superfluorescence properties of the new materials were demonstrated under femtosecond excitation in liquid media, providing among the highest known FOM for organic compounds in liquid solution to date. To further understand ultrafast dynamics of these molecules, the nature of fast excited-state relaxation processes in 1 and 2 with characteristic times of ∼0.2−3 ps was revealed via femtosecond transient absorption pump−probe spectroscopy. The electronic, linear optical, and nonlinear optical properties of 1 and 2 were modeled with quantum-chemical calculations. The 1PA and 2PA spectra obtained in the TD-CAM-B3LYP approach were in good agreement with the experimental data. However, theoretically predicted 2PA spectra do not account for the first experimental maxima, and can likely be accounted H



Article

Polymerization Using a Fluorone/Amine Initiating System. J. Am. Chem. Soc. 2000, 122, 1217−1218. (11) Kawata, S.; Kawata, Y. Three-Dimensional Optical Data Storage Using Photochromic Materials. Chem. Rev. 2000, 100, 1777−1788. (12) Pimenta, F. M.; Jensen, R. L.; Holmegaard, L.; Esipova, T. V.; Westberg, M.; Breitenbach, T.; Ogilby, P. R. Singlet-Oxygen-Mediated Cell Death Using Spatially-Localized Two-Photon Excitation of an Extracellular Sensitizer. J. Phys. Chem. B 2012, 116, 10234−10246. (13) Beverina, L.; Crippa, M.; Landenna, M.; Ruffo, R.; Salice, P.; Silvestri, F.; Versari, S.; Villa, A.; Ciaffoni, L.; Collini, E.; et al. Assessment of Water-Soluble π-Extended Squaraines as One- and Two-Photon Singlet Oxygen Photosensitizers: Design, Synthesis, and Characterization. J. Am. Chem. Soc. 2008, 130, 1894−1902. (14) Oar, M. A.; Serin, J. M.; Ditchel, W. R.; Fréchet, J. M. J.; Ohulchanskyy, T. Y.; Prasad, P. N. Photosensitization of Singlet Oxygen Via Two-Photon-Excited Fluorescence Resonance Energy Transfer in a Water-Soluble Dendrimer. Chem. Mater. 2005, 17, 2267−2275. (15) Franckevicius, M.; Vaišnoras, R.; Marcos, M.; Serrano, J. L.; Gulbinas, V. Excited State Dynamics of PPI Dendrimers Functionalized with 4-(4′-Ethoxybenzoyloxy)Salicylaldehyde Chromophores. Chem. Phys. 2013, 412, 77−83. (16) Peng, H.-L.; Payton, J. L.; Protasiewicz, J. D.; Simpson, M. C. π=π Bond Photophysics in an Ar−π=π−Ar Diphosphene. Dalton Trans. 2012, 41, 13204−13209. (17) Etzold, F.; Howard, I. A.; Forler, N.; Cho, D. M.; Meister, M.; Mangold, H.; Shu, J.; Hansen, M. R.; Müllen, K.; Laquai, F. The Effect of Solvent Additives on Morphology and Excited-State Dynamics in PCPDTBT:PCBM Photovoltaic Blends. J. Am. Chem. Soc. 2012, 134, 10569−10583. (18) Donnert, G.; Keller, J.; Medda, R.; Andrei, M. A.; Rizzoli, S. O.; Luhrmann, R.; Jahn, R.; Eggeling, C.; Hell, S. W. MacromolecularScale Resolution in Biological Fluorescence Microscopy. Proc. Natl. Acad. Sci. U.S.A. 2006, 103, 11440−11445. (19) Fischer, J.; Freymann, G. V.; Wegener, M. The Materials Challenge in Diffraction-Unlimited Direct-Laser-Writing Optical Lithography. Adv. Mater. 2010, 22, 3578−3582. (20) Luo, D.; Kuang, C.; Liu, X.; Wang, G. Experimental Investigations on Fluorescence Excitation and Depletion of ATTO 390 Dye. Opt. Laser Technol. 2013, 45, 723−725. (21) He, G. S.; Yuan, L.; Cui, Y.; Li, M.; Prasad, P. N. Studies of Two-Photon Pumped Frequency-Upconverted Lasing Properties of a New Dye Material. J. Appl. Phys. 1997, 81, 2529−2537. (22) Kim, H.; Schulte, N.; Zhou, G.; Müllen, K.; Laquai, F. A. A High Gain and High Charge Carrier Mobility Indenofluorene-Phenanthrene Copolymer for Light Amplification and Organic Lasing. Adv. Mater. 2011, 23, 894−897. (23) Belfield, K. D.; Andrade, C. D.; Yanez, C. O.; Bondar, M. V.; Hernandez, F. E.; Przhonska, O. V. New Two-Photon-Absorbing Probe with Efficient Superfluorescent Properties. J. Phys. Chem. B 2010, 114, 14087−14095. (24) Zhou, D.; Khatmullin, R.; Walpita, J.; Miller, N. A.; Luk, H. L.; Vyas, S.; Hadad, C. M.; Glusac, K. D. Mechanistic Study of the Photochemical Hydroxide Ion Release from 9-Hydroxy-10-methyl-9phenyl-9,10-dihydroacridine. J. Am. Chem. Soc. 2012, 134, 11301− 11303. (25) Nishiyama, Y.; Terazima, M.; Kimura, Y. Ultrafast Relaxation and Reaction of Diiodide Anion after Photodissociation of Triiodide in Room-Temperature Ionic Liquids. J. Phys. Chem. B 2012, 116, 9023− 9032. (26) Scrutton, N. S.; Groot, M. L.; Heyes, D. J. Excited State Dynamics and Catalytic Mechanism of the Light-Driven Enzyme Protochlorophyllide Oxidoreductase. Phys. Chem. Chem. Phys. 2012, 14, 8818−8824. (27) Ichinose, N.; Hagiri, M.; Kinugasa, J.; Shichi, N.; Nakayama, T. Study on Excited States of Hexamethoxybenzene-No+ ChargeTransfer Complex: Incorporation of Excited Radical Cation. Res. Chem. Intermed. 2013, 39, 425−435.

(28) Boo, B. H.; Cho, H.; Kim, Y. M.; Lee, S. J. Transient Absorption Spectroscopy of Bis(4,4-Dimethyl-2,5-Cyclohexadien-1-Ylidene). Elucidation of Triplet-State Geometry and Triplet-Triplet Absorption. Bull. Korean Chem. Soc. 2012, 33, 3879−3882. (29) Guo, H.; Li, Q.; Ma, L.; Zhao, J. Fluorene as π-Conjugation Linker in N̂ N Pt(Ii) Bisacetylide Complexes and Their Applications for Triplet−Triplet Annihilation Based Upconversion. J. Mater. Chem. 2012, 22, 15757−15768. (30) Fita, P.; Garbacz, P.; Nejbauer, M.; Radzewicz, C.; Waluk, J. Ground and Excited State Double Hydrogen Transfer in Symmetric and Asymmetric Potentials: Comparison of 2,7,12,17-Tetra-NPropylporphycene with 9-Acetoxy-2,7,12,17-Tetra-N-Propylporphycene. Chem.Eur. J. 2011, 17, 3672−3678. (31) Yang, P.; Zhao, J.; Wu, W.; Yu, X.; Liu, Y. Accessing the LongLived Triplet Excited States in Bodipy-Conjugated 2-(2-Hydroxyphenyl) Benzothiazole/Benzoxazoles and Applications as Organic Triplet Photosensitizers for Photooxidations. J. Org. Chem. 2012, 77, 6166−6178. (32) Ciuciu, A. I.; Skonieczny, K.; Koszelewski, D.; Gryko, D. T.; Flamigni, L. Dynamics of Intramolecular Excited State Proton Transfer in Emission Tunable, Highly Luminescent Imidazole Derivatives. J. Phys. Chem. C 2013, 117, 791−803. (33) Carlotti, B.; Kikas, I.; Skoric, I.; Spalletti, A.; Elisei, F. Photophysics of Push−Pull Distyrylfurans, Thiophenes and Pyridines by Fast and Ultrafast Techniques. ChemPhysChem 2013, 14, 970−981. (34) Józefowicz, M.; Fita, P.; Kasprzycki, P.; Heldt, J. R. Excited-State Dynamics of Ethyl 5-(4-Aminophenyl)-3-Amino-2,4-Dicyanobenzoate. J. Phys. Chem. A 2013, 117, 4136−4147. (35) Peckus, D.; Devižis, A.; Augulis, R.; Graf, S.; Hertel, D.; Meerholz, K.; Gulbinas, V. Charge Transfer States in Merocyanine Neat Films and Its Blends with [6,6]-Phenyl-C61-Butyric Acid Methyl Ester. J. Phys. Chem. C 2013, 117, 6039−6048. (36) Durchan, M.; Fuciman, M.; Šlouf, V.; Keşan, G.; Polívka, T. Excited-State Dynamics of Monomeric and Aggregated Carotenoid 8′Apo-B-Carotenal. J. Phys. Chem. A 2012, 116, 12330−12338. (37) Lohse, P. W.; Kuhnt, J.; Druzhinin, S. I.; Scholz, M.; Ekimova, M.; Oekermann, T.; Lenzer, T.; Oum, K. Ultrafast Photoinduced Relaxation Dynamics of the Indoline Dye D149 in Organic Solvents. Phys. Chem. Chem. Phys. 2011, 13, 19632−19640. (38) Consani, C.; Auböck, G.; Van Mourik, F.; Chergui, M. Ultrafast Tryptophan-to-Heme Electron Transfer in Myoglobins Revealed by UV 2D Spectroscopy. Science 2013, 339, 1586−1589. (39) Muro-Small, M. L.; Yarnell, J. E.; McCusker, C. E.; Castellano, F. N. Spectroscopy and Photophysics in Cyclometalated Ruii− Bis(Bipyridyl) Complexes. Eur. J. Inorg. Chem. 2012, 4004−4011. (40) Iwamura, M.; Nozaki, K.; Takeuchi, S.; Tahara, T. Real-Time Observation of Tight Au−Au Bond Formation and Relevant Coherent Motion Upon Photoexcitation of [Aucn)2−] Oligomers. J. Am. Chem. Soc. 2013, 135, 538−541. (41) Maroncelli, M.; Fleming, G. R. Picosecond Solvation Dynamics of Coumarin 153: The Importance of Molecular Aspects of Solvation. J. Chem. Phys. 1987, 86, 6221−6239. (42) Chudoba, C.; Nibbering, E. T. J.; Elsaesser, T. Site-Specific Excited-State Solute-Solvent Interactions Probed by Femtosecond Vibrational Spectroscopy. Phys. Rev. Lett. 1998, 81, 3010−3013. (43) Lepkowicz, R. S.; Przhonska, O. V.; Hales, J. M.; Hagan, D. J.; Van Stryland, E. W.; Bondar, M. V.; Slominsky, Y. L.; Kachkovski, A. D. Excited-State Absorption Dynamics in Polymethine Dyes Detected by Polarization-Resolved Pump-Probe Measurements. Chem. Phys. 2003, 286, 277−291. (44) Miyasaka, H.; Murakami, M.; Okada, T.; Nagata, Y.; Itaya, A.; Kobatake, S.; Irie, M. Picosecond and Femtosecond Laser Photolysis Studies of a Photochromic Diarylethene Derivative: Multiphoton Gated Reaction. Chem. Phys. Lett. 2003, 371, 40−48. (45) Ellinger, S.; Graham, K. R.; Shi, P.; Farley, R. T.; Steckler, T. T.; Brookins, R. N.; Taranekar, P.; Mei, J.; Padilha, L. A.; Ensley, T. R.; et al. Donor-Acceptor-Donor-Based π-Conjugated Oligomers for Nonlinear Optics and near-IR Emission. Chem. Mater. 2011, 23, 3805−3817. I



Article

(46) Kato, S.; Matsumoto, T.; Shigeiwa, M.; Gorohmaru, H.; Maeda, S.; Ishi-i, T.; Mataka, S. Novel 2,1,3-Benzothiadiazole-Based RedFluorescent Dyes with Enhanced Two-Poton Asorption Coss-Sctions. Chem.Eur. J. 2006, 12, 2303−2317. (47) Ruan, Y.-B.; Yu, Y.; Li, C.; Bogliotti, N.; Tang, J.; Xie, J. Triazolyl Benzothiadiazole Fluorescent Chemosensors: A Systematic Investigation of 1,4- or 1,5-Disubstituted Mono- and Bis-Triazole Derivatives. Tetrahedron 2013, 69, 4603−4608. (48) Kitamura, C.; Tanaka, S.; Yamashita, Y. Design of NarrowBandgap Polymers. Syntheses and Properties of Monomers and Polymers Containing Aromatic-Donor and O-Quinoid-Acceptor Units. Chem. Mater. 1996, 8, 570−578. (49) Peng, Q.; Lim, S.-L.; Wong, I. H.-K.; Xu, J.; Chen, Z.-K. Synthesis and Photovoltaic Properties of Two-Dimensional LowBandgap Copolymers Based on New Benzothiadiazole Derivatives with Different Conjugated Arylvinylene Side Chains. Chem.Eur. J. 2012, 18, 12140−12151. (50) Cheng, Y.-J.; Yang, S.-H.; Hsu, C.-S. Synthesis of Conjugated Polymers for Organic Solar Cell Applications. Chem. Rev. 2009, 109, 5868−5923. (51) Peng, Q.; Liu, X.; Su, D.; Fu, G.; Xu, J.; Dai, L. Novel Benzo[1,2-B:4,5-B′]Dithiophene-Benzothiadiazole Derivatives with Variable Side Chains for High-Performance Solar Cells. Adv. Mater. 2011, 23, 4554−4558. (52) Chen, L.; Li, P.; Cheng, Y.; Xie, Z.; Wang, L.; Jing, X.; Wang, F. White Electroluminescence from Star-Like Single Polymer Systems: 2,1,3-Benzothiadiazole Derivatives Dopant as Orange Cores and Polyfluorene Host as Six Blue Arms. Adv. Mater. 2011, 23, 2986−2990. (53) Oliveira, F. F. D.; Santos, D. C. B. D.; Lapis, A. A. M.; Corrêa, J. R.; Gomes, A. F.; Gozzo, F. C.; Moreira, P. F., Jr.; de Oliveira, V. C.; Quina, F. H.; Neto, B. A. D. On the Use of 2,1,3-Benzothiadiazole Derivatives as Selective Live Cell Fluorescence Imaging Probes. Bioorg. Med. Chem. Lett. 2010, 20, 6001−6007. (54) Neto, B. A. D.; Corrêa, J. R.; Carvalho, P. H. P. R.; Santos, D. C. B. D.; Guido, B. C.; Gatto, C. C.; de Oliveira, H. C. B.; Fasciotti, M.; Eberlin, M. N.; da Silva, E. N., Jr. Selective and Efficient Mitochondrial Staining with Designed 2,1,3-Benzothiadiazole Derivatives as Live Cell Fluorescence Imaging Probes. J. Braz. Chem. Soc. 2012, 23, 770−781. (55) Karikomi, M.; Kitamura, C.; Tanaka, S.; Yamashita, Y. New Narrow-Bandgap Polymer Composed of Benzobis(L,2,5-Thiadiazole) and Thiophenes. J. Am. Chem. Soc. 1995, 117, 6791−6792. (56) Hodgkiss, J. M.; Tu, G.; Albert-Seifried, S.; Huck, W. T. S.; Friend, R. H. Ion-Induced Formation of Charge-Transfer States in Conjugated Polyelectrolytes. J. Am. Chem. Soc. 2009, 131, 8913−8921. (57) Cowan, S. R.; Leong, W. L.; Banerji, N.; Dennler, G.; Heeger, A. J. Identifying a Threshold Impurity Level for Organic Solar Cells: Enhanced First-Order Recombination Via Well-Defined Pc84bm Traps in Organic Bulk Heterojunction Solar Cells. Adv. Funct. Mater. 2011, 21, 3083−3092. (58) Lakowicz, J. R. Principles of Fluorescence Spectroscopy; Kluwer: New York, 1999. (59) Belfield, K. D.; Bondar, M. V.; Morales, A. R.; Yue, X.; Luchita, G.; Przhonska, O. V. Transient Excited-State Absorption and Gain Spectroscopy of a Two-Photon Absorbing Probe with Efficient Superfluorescent Properties. J. Phys. Chem. C 2012, 116, 11261− 11271. (60) Magde, D.; Wong, R.; Seybold, P. G. Fluorescence Quantum Yields and Their Relation to Lifetimes of Rhodamine 6G and Fluorescein in Nine Solvents: Improved Absolute Standards for Quantum Yields. Photochem. Photobiol. 2002, 75, 327−334. (61) Corredor, C. C.; Belfield, K. D.; Bondar, M. V.; Przhonska, O. V.; Yao, S. One- and Two-Photon Photochemical Stability of Linear and Branched Fluorene Derivatives. J. Photochem. Photobiol. A 2006, 184, 105−112. (62) Belfield, K. D.; Bondar, M. V.; Morales, A. R.; Yue, X.; Luchita, G.; Przhonska, O. V.; Kachkovsky, O. D. Two-Photon Absorption and Time-Resolved Stimulated Emission Depletion Spectroscopy of a New Fluorenyl Derivative. ChemPhysChem 2012, 13, 3481−3491.

(63) Sheik-Bahae, M.; Said, A. A.; Wei, T. H.; Hagan, D. J.; Van Stryland, E. W. Sensitive Measurement of Optical Nonlinearities Using a Single Beam. IEEE J. Quantum Electron. 1990, 26, 760−769. (64) Belfield, K. D.; Bondar, M. V.; Morales, A. R.; Frazer, A.; Mikhailov, I. A.; Przhonska, O. V. Photophysical Properties and Ultrafast Excited-State Dynamics of a New Two-Photon Absorbing Thiopyranyl Probe. J. Phys. Chem. C 2013, 117, 11941−11952. (65) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; et al. Gaussian 09, Revision A.2; Gaussian, Inc.: Wallingford, CT, 2009. (66) Yanai, T.; Tew, D. P.; Handy, N. C. A New Hybrid Exchange− Correlation Functional Using the Coulomb-Attenuating Method (CAM-B3LYP). Chem. Phys. Lett. 2004, 393, 51−57. (67) Stephens, P. J.; Devlin, F. J.; Chabalowski, C. F.; Frisch, M. J. Ab Initio Calculation of Vibrational Absorption and Circular Dichroism Spectra Using Density Functional Force Fields. J. Phys. Chem. 1994, 98, 11623−11627. (68) Hehre, W. J.; Ditchfield, R.; Pople, J. A. Self-Consistent Molecular Orbital Methods. XII. Further Extensions of Gaussian Type Basis Sets for Use in Molecular Orbital Studies of Organic Molecules. J. Phys. Chem. 1972, 56, 2257−2261. (69) Mikhailov, I. A.; Bondar, M. V.; Belfield, K. D.; Masunov, A. E. Electronic Properties of a New Two-Photon Absorbing Fluorene Derivative: The Role of Hartree-Fock Exchange in the Density Functional Theory Design of Improved Nonlinear Chromophores. J. Phys. Chem. C 2009, 113, 20719−20724. (70) Masunov, A.; Tretiak, S. Prediction of Two-Photon Absorption Properties for Organic Chromophores Using Time-Dependent Density- Functional Theory. J. Phys. Chem. B 2004, 108, 899−907. (71) Nelson, T.; Fernandez-Alberti, S.; Chernyak, V.; Roitberg, A. E.; Tretiak, S. Nonadiabatic Excited-State Molecular Dynamics Modeling of Photoinduced Dynamics in Conjugated Molecules. J. Phys. Chem. B 2011, 115, 5402−5414. (72) Ohta, K.; Antonov, L.; Yamada, S.; Kamada, K. Theoretical Study of the Two-Photon Absorption Properties of Several Asymmetrically Substituted Stilbenoid Molecules. J. Chem. Phys. 2007, 127, 084504/1−12. (73) Rumi, M.; Ehrlich, J. E.; Heikal, A. A.; Perry, J. W.; Barlow, S.; Hu, Z. Y.; McCord-Maughon, D.; Parker, T. C.; Rockel, H.; Thayumanavan, S.; et al. Structure-Property Relationships for TwoPhoton Absorbing Chromophores: Bis-Donor Diphenylpolyene and Bis(Styryl)Benzene Derivatives. J. Am. Chem. Soc. 2000, 122, 9500− 9510. (74) Beaujuge, P. M.; Amb, C. M.; Reynolds, J. R. Spectral Engineering in π-Conjugated Polymers with Intramolecular DonorAcceptor Interactions. Acc. Chem. Res. 2010, 43, 1396−1407. (75) Gong, Y.; Guo, X.; Wang, S.; Su, H.; Xia, A.; He, Q.; Bai, F. Photophysical Properties of Photoactive Molecules with Conjugated Push-Pull Structures. J. Phys. Chem. A 2007, 111, 5806−5812. (76) Strickler, S. J.; Berg, R. A. Relationship between Absorption Intensity and Fluorescence Lifetime of Molecules. J. Chem. Phys. 1962, 3, 814−822. (77) El-Daly, S. A.; El-Azim, S. A.; Elmekawey, F. M.; Elbaradei, B. Y.; Shama, S. A.; Asiri, A. M. Photophysical Parameters, Excitation Energy Transfer, and Photoreactivity of 1,4-Bis(5-Phenyl-2-Oxazolyl)Benzene (Popop) Laser Dye. Int. J. Photoenergy 2012, 2012, 458126/ 1−10. (78) Rosenthal, I. Photochemical Stability of Rhodamine 6G in Solution. Opt. Commun. 1978, 24, 164−166. (79) Xia, T.; Hagan, D. J.; Dogariu, A.; Said, A. A.; Van Stryland, E. W. Optimization of Optical Limiting Devices Based on Excited-State Absorption. Appl. Opt. 1997, 36, 4110−4122. (80) Zhou, G.-Y.; Wang, C.; Lei, H.; Wang, D.; Shao, Z.-S.; Jiang, M.H. Two-Photon Absorption and Optical Power Limiting Based on New Organic Dyes. Chin. Phys. Lett. 2001, 18, 1120−1122. (81) Enciso, E.; Costela, A.; Garcia-Moreno, I.; Martin, V.; Sastre, R. Conventional Unidirectional Laser Action Enhanced by Dye Confined in Nanoparticle Scatters. Langmuir 2010, 26, 6154−6157. J



Article

(82) Zhang, D.; Wang, Y.; Ma, D. SiO2 Nanoparticles as Scatterers for Random Organic Laser Action in Red fluorescent Dye 4(Dicyanomethylene)-2-Tert-Butyl-6(1,1,7,7-Tetramethyljulolidyl-9Enyl)-4h-Pyran Doped Polystyrene films. J. Appl. Phys. 2008, 103, 123107/1−4. (83) Shafer, F. P. Dye Lasers; Springer-Verlag: New York, 1973; p 285. (84) Kwon, J. E.; Park, S. Y. Advanced Organic Optoelectronic Materials: Harnessing Excited-State Intramolecular Proton Transfer (Esipt) Process. Adv. Mater. 2011, 23, 3615−3642. (85) Fita, P.; Fedoseeva, M.; Vauthey, E. Ultrafast Excited-State Dynamics of Eosin B: A Potential Probe of the Hydrogen-Bonding Properties of the Environment. J. Phys. Chem. A 2011, 115, 2465− 2470. (86) Kosumi, D.; Maruta, S.; Fujii, R.; Kanemoto, K.; Sugisaki, M.; Hashimoto, H. Ultrafast Excited State Dynamics of Monomeric Bacteriochlorophyll A. Phys. Status Solidi C 2011, 8, 92−95. (87) Golibrzuch, K.; Ehlers, F.; Scholz, M.; Oswald, R.; Lenzer, T.; Oum, K.; Kim, H.; Koo, S. Ultrafast Excited State Dynamics and Spectroscopy of 13,13′-Diphenyl-B-Carotene. Phys. Chem. Chem. Phys. 2011, 13, 6340−6351. (88) Pozdnyakov, I. P.; Kolomeets, A. V.; Plyusnin, V. F.; Melnikov, A. A.; Kompanets, V. O.; Chekalin, S. V.; Tkachenko, N.; Lemmetyinen, H. Photophysics of Fe(III)−Tartrate and Fe(III)− Citrate Complexes in Aqueous Solutions. Chem. Phys. Lett. 2012, 530, 45−48. (89) Efimova, S. L.; Malyukin, Y. V. Franck-Condon State Relaxation in Some Pyrazoline Luminophor. Funct. Mater. 2002, 9, 247−250. (90) Gustavsson, T.; Cassara, L.; Gulbinas, V.; Gurzadyan, G.; Mialocq, J.-C.; Pommeret, S.; Sorgius, M.; van der Meulen, P. Femtosecond Spectroscopic Study of Relaxation Processes of Three Amino-Substituted Coumarin Dyes in Methanol and Dimethyl Sulfoxide. J. Phys. Chem. A 1998, 102, 4229−4245. (91) Taylor, A. J.; Erskine, D. J.; Tang, C. L. Femtosecond Vibrational Relaxation of Large Organic Molecules. Chem. Phys. Lett. 1984, 103, 430−435.

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