Article pubs.acs.org/JPCC
Aqueous Nanoaggregation-Enhanced One- and Two-Photon Fluorescence, Crystalline J-Aggregation-Induced Red Shift, and Amplified Spontaneous Emission of 9,10-Bis(pdimethylaminostyryl)anthracene Yalong Wang, Tongliang Liu, Lingyu Bu, Jinfeng Li, Chao Yang, Xiaojing Li, Yong Tao, and Wenjun Yang* Key Laboratory of Rubber-Plastics of Ministry of Education/Shandong Provincial Key Laboratory of Rubber-plastics, Qingdao University of Science & Technology, 53-Zhengzhou Road, Qingdao, 266042, China ABSTRACT: We have synthesized two 9,10-bis(pdialkylaminostyryl)anthracene derivatives, 9,10-bis(pdimethylaminostyryl)anthracene (9,10-MADSA), and 9,10bis(p-dipropylaminostyryl)anthracene (9,10-PADSA), and the photophysical properties in solution, aqueous suspension, and crystalline state are comparatively investigated. Their twisted conjugated skeleton and D-π-D pattern make the molecular solution show weak fluorescence and the aqueous suspension exhibit aggregation-induced one- and two-photon emission. The crystals of 9,10-MADSA display high fluorescence efficiency (59.4%) and unusual red-shifted emission (586 nm) compared with that in solution and aqueous suspension, which is different from its homologue 9,10-PADSA that is yellow-emitting crystal (553 nm) with the fluorescence efficiency of 29.2%. Moreover, the amplified spontaneous emission effect is observed only from the single crystal of 9,10-MADSA. The origin of these unique photophysical properties for 9,10-MADSA crystals is ascribed to its specific packing mode, J-aggregation. This work demonstrates that the subtle manipulation of end groups of 9,10-divinylanthracene derivatives could significantly influence the molecular packing in crystals and endow them with novel optical properties.
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was first demonstrated by Prasad et al. in 9,10-bis-[4′-(4″aminostyryl)styryl]anthracene (BDSA-Bz)6 and used in twopohton fluorescence imaging and photodynamic therapy.1 Recently, Tian et al.7 have reported that 9,10-di(alkoxystyryl)anthracenes exhibited strong AIE effect and crystal fluorescence, 9,10-di(p-methylstyryl)anthracene showed amplified spontaneous emission (ASE) in its single crystal form, and phenol-moiety-containing and ammonium-salt-containing 9,10DSA derivatives could sense pH and biomacromolecules. Chi et al.8 have demonstrated that some of the 9,10-DSA derivatives end-capped with bulky tetraphenylethene or triphenylethylenetriphenylamine and so on displayed piezochromic fluorescence. These results imply that the subtle manipulation of end groups of 9,10-DSA could endow them with novel optical properties. In the current work, we synthesize two single-available 9,10DSA derivatives, 9,10-bis(p-dimethylaminostyryl)anthracene (9,10-MADSA) and 9,10-bis(p-dimethylaminostyryl)anthracene (9,10-PADSA). They are AIE/CEE-active compounds with a typical D-π-D structure, and our primary goal is to examine whether the twisted conjugated skeleton bearing electron-donating end groups could endow them with unique
INTRODUCTION Organic fluorophores exhibiting high nanoaggregation-induced emission and solid- and crystalline-state fluorescence efficiency have received increasing attention owing to their potential applications in fluorescence imaging, light-emitting devices, and active gain media for optically pumped solid-state lasers.1−3 However, most fluorescent organic materials show the aggregation- or crystallization-caused quenching (ACQ) effect due to strong π−π stacking interactions, which is a typical problem of common organic chromophores.4 Recently, some conjugated molecules with twisted skeleton conformation have been demonstrated to exhibit aggregation-induced emission (AIE) or crystallization-enhanced emission (CEE) effects,5 which are mainly ascribed to the restriction of intramolecular rotation or conformation planarization in the aggregates. The emergence of these new π-conjugated organic materials started to draw serious research attention only within the past decade and has widened the scope of molecular candidates applicable in optics and optoelectronics. Up to now, there have been a variety of conjugated molecules with AIE/CEE properties reported in the literature,5 such as siloles, CN-MBE, DPDSB derivatives, DPDBF derivatives, conjugated polymers, and others. Among them, 9,10-distyrylanthracene (9,10-DSA) derivatives are also a class of promising and attractive AIE/ CEE molecules. The AIE phenomenon of 9,10-DSA derivatives © 2012 American Chemical Society
Received: April 1, 2012 Revised: June 19, 2012 Published: July 3, 2012 15576
dx.doi.org/10.1021/jp3031094 | J. Phys. Chem. C 2012, 116, 15576−15583
The Journal of Physical Chemistry C
Article
fluorescence properties in the crystalline state and strong twophoton activities in the aqueous medium. We now report that 9,10-bis(p-dialkylaminostyryl)anthracenes exhibit aggregationenhanced one- and two-photon excitated fluorescence in aqueous media, and 9,10-MADSA shows a very high fluorescence efficiency (Φc = 59.4%), an unusual red emission (λem = 586 nm), and ASE effect in the single-crystal form resulting from its specific packing mode, J-aggregation.
this reference have been well-documented in the literature.11 The intensities of the two-photon-induced fluorescence spectra of the reference and sample emitted at the same excitation wavelength were determined. The TPA cross section, measured by using the two-photon-induced fluorescence measurement technique, can be measured by using the following equation
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δS =
EXPERIMENTAL SECTION General. Tetrahydrofuran (THF) was distillated over metallic sodium before use. Other solvents and reagents (analytical grade) were used as received, unless otherwise claimed. The NMR spectra were recorded on a Bruker-AC500 (500 MHz) spectrometer in CDCl3 with tetramethylsilane (TMS) as the standard. The elemental analysis was performed on Perkin−Elmer 2400. UV−vis absorption spectra were recorded on a UV-4100 spectrophotometer. One-photon fluorescence measurements were carried out with F-4600 fluorescence spectrophotometer. Crystalline-state PL efficiencies were measured on an integrating sphere (C-701, Labsphere) with a 325 nm Xe light as the excitation source, and the laser was introduced into the sphere through the optical fiber. Single crystals of the compounds were slowly prepared by simple vapor-diffusion method from the dichloromethane−methanol system at room temperature under rigorous exclusion of light. The single-crystal X-ray diffraction experiments were carried out on a Rigaku R-AXIS RAPID diffractometer equipped with a Mo Kα and Control Software using RAPID AUTO at 293(±2) °C. The structures were solved with direct methods and refined with a full-matrix leastsquares technique using the SHELXS v.5.1 programs, respectively. The space groups were determined from the systematic absences, and their correctness was confirmed by successful solution and refinement of structures. Preparation of Aqueous Nanoaggregate Suspension. Samples for the measurement of one-photon properties: An aliquot (1 mL) of stock THF solution of the compounds with a concentration of 1 × 10−4 M was slowly added to a certain amount of D.I. water with vigorous stirring, and concentration was kept at 1.0 × 10−5 M. Two-photon properties: An aliquot (1 mL) of stock THF solution of 9,10-PADSA with a concentration of 1 × 10−2 M was added slowly to 9 mL of D.I. water with vigorous stirring to form an aqueous suspension with the concentration of 1.0 × 10−3 M. These aqueous suspensions were stable during the measurement. Two-Photon Excitation Fluorescence and Absorption Cross Section. The two-photon excitation fluorescence (TPEF) spectra of 9,10-PADSA were measured by using the femtosecond laser pulses at 800 nm and under the input laser power of 48−196 mW. The excitation light source was a modelocked Ti:sapphire femtosecond laser (Spectra-Physics, Tsunami 3941, 700−910 nm, 80 MHz,
