Pyrenyl-Capped Benzofiurene Derivatives: Synthesis

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Pyrenyl-Capped Benzofiurene Derivatives: Synthesis, Characterization, and the Effects of Flexible Side Chains on Modulating the Optoelectronic Properties Yi Jiang, Cheng Cheng, Jin-Jin Huang, Ling-Wei Feng, Xin Guo, Cheng-Fang Liu, Xin-Wen Zhang, Wen-Yong Lai, and Wei Huang J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.5b09719 • Publication Date (Web): 27 Nov 2015 Downloaded from http://pubs.acs.org on December 5, 2015

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The Journal of Physical Chemistry

Pyrenyl-Capped Benzofiurene Derivatives: Synthesis, Characterization, and the Effects of Flexible Side Chains on Modulating the Optoelectronic Properties Yi Jiang,† Cheng Cheng,† Jin-Jin Huang,† Ling-Wei Feng,† Xin Guo,† Cheng-Fang Liu,† Xin-Wen Zhang,† Wen-Yong Lai,*, † Wei Huang*, ‡ †

Key Laboratory for Organic Electronics and Information Displays (KLOEID) & Institute of

Advanced Materials (IAM), Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM), Nanjing University of Posts & Telecommunications, 9 Wenyuan Road, Nanjing 210023, China ‡

Key Laboratory of Flexible Electronics (KLOFE) & Institute of Advanced Materials (IAM),

Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM), Nanjing Tech University (NanjingTech), 30 South Puzhu Road, Nanjing 211816, China *Email: [email protected] (W. Y. Lai); [email protected] (W. Huang)

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ABSTRACT: A new series of pyrenyl-capped benzofiurene derivatives (PFP-1, PFP-2, PFP-3, and PFP-4) were designed, synthesized and investigated as model compounds for understanding the effects of flexible side chains on modulating the functional properties of organic semiconductors for optoelectronics. The resulting compounds exhibited high fluorescence yields (changing from 28% for PFP-1 to 46% for PFP-3), good thermal stability (increasing from 439 °C for PFP-4 to 510 °C for PFP-1) and fair glass-transition temperatures (ranging from 84 °C for PFP-4 to 175 °C for PFP-1). According to ultraviolet absorption (UV) and photoluminescence (PL) spectra, the long flexible side chains on diaryl substituents have played an important role on influencing the intermolecular interactions and radiative deactivation decays. Moreover, the flexible side chains on diaryl substituents also influence the process of exciton migration and exciton quenching, further resulting in different photoluminescence quantum yield (PLQY) and transient lifetimes for PFP-X. As evidenced by atomic force microscopy (AFM) images and X-ray diffraction (XRD) patterns, an increase in the lengths of flexible chain substituents can effectively depress the crystalline nature of the rigid conjugated molecular backbone, which can endow the corresponding materials with improved morphology properties. The solution-processed nondoped organic light-emitting diodes (OLEDs) based on PFP-3 showed high efficiency (up to 2.56 cd/A and 8372 cd/m2) and bright blue-light emission with Commission Intermationale de L’Eclairage (CIE) coordinates of (0.15, 0.15). It is worthwhile to mention that the performance of these solution-processed OLEDs is comparable to and even better than that of vacuum-deposited OLEDs. One dimensional (1D) distributed feedback lasers using PFP-3 as gain media were constructed with a tunable wavelength ranging from 456.0 nm to 471.4 nm and low pump energy thresholds (0.28 KW/cm2), which is among the best results achieved from small molecular gain media. This study emphasizes that subtle structural alteration even for flexible side chains can significantly 2 ACS Paragon Plus Environment

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affect the corresponding characteristics, which are vital for rational design of the molecular structures for optoelectronic applications. INTRODUCTION π-Conjugated semiconductors have received immense attention in recent years owing to low-cost, large-area manufacturing by solution processing and tunable optoelectronic properties through a convenient molecular design, which make them potential materials for various applications such as organic light-emitting diodes (OLEDs),1-3 organic photovoltaic cells (OPVs),

4-7

and organic

thin-film transistors (OTFTs).8-14 It is well established that the device performance based on organic semiconductors heavily depends on the solid-state structures. From this perspective, understanding the relationship between the structure and the property is critically important. In the past decades, tremendous efforts have been focused on the rational design of π-conjugated backbones,1-16 while the effects of flexible chains, which are usually used as solubilizing groups, on the functional optoelectronic properties have attracted much less attention.17-20 Generally speaking, the attachment of flexible chains to π-conjugated backbones can improve the solubility in common solvents, which is crucial for solution processing and the film-forming ability. However, there is little literature unravelling the relationships between flexible chains and functional optoelectronic properties, such as luminous efficiency and especially lasing performance.21 As far as we are concerned, flexible chains may have a crucial impact on molecular packing and thin-film morphology, and hence on device performance.22-26 It is therefore of our great interest to construct a set of model samples to investigate the structure-property relationships by modulating the flexible side chains including the influences of types, length, symmetry, and branching points. 3 ACS Paragon Plus Environment


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Fluorene based compounds are considered to be the most promising blue light-emitting materials because of their high photoluminescence (PL) efficiencies, good thermal stabilities and easy tunability of properties by substitution at the C9 position. Unfortunately, long-wavelength emission bands upon annealing or passage of current, which lead to poor spectral stabilities, have hampered their practical applications.27-30 In contrast to fluorene based molecules, pyrene molecules have outstanding thermal stability in addition to their high photoluminescence.31 However, in the case of the solid state, planar pyrene molecules are likely to form aggregate/excimer, giving rise to red-shifted emission.31 In order to solve this problem, the introduction of bulky substituents to their molecular structures can successfully prevent the molecular packing and hence result in excellent film-forming abilities and morphological stability.32 We have recently reported a series of fluorene-pyrene hybrids based on 2,7-disubstituted fluorene, which demonstrated not only interesting photophysical properties and morphological stability but also excellent OLED performance.33-36 Consequently, we surmise that the integration of fluorene and pyrene into a molecular structure can impart favourable optical and charge transport properties for optoelectronic applications. In this work, we present the design, synthesis and structure-property relationships of a novel set of pyrenyl-capped benzofiurene derivatives (PFP-1, PFP-2, PFP-3, and PFP-4, Scheme 1). Pyrenyl-capped benzofiurene was selected as the molecular backbone and the flexible chains on diaryl substituents at C9 position of the fluorene units were varied with the aim to provide a set of model samples to unravel the effects of flexible side chains on modulating the functional properties of organic semiconductors for optoelectronics. By using the techniques of UV/PL spectra, fluorescence transient spectroscopy and quantum chemical calculations, the influences of flexible 4 ACS Paragon Plus Environment

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side chains with varing types, length, symmetry, and branching points were investigated. The corresponding morphology and packing structure were studied by atomic force microscopy (AFM) and X-ray diffraction (XRD). Highly efficient solution-processed blue OLEDs based on the small molecules with favourable long flexible side chains exhibited impressive characteristics and achieved comparable performance to those devices employing vacuum deposition. In this case, proper modulation of the flexible side chains enabled the resulting small molecules with solution processability, overcoming the disadvantages of vacuum deposition such as complex fabrication and high cost. Owing to their good solubility and film-forming properties, PFP-3 and PFP-4 were selected as gain media to investigate their lasing behaviours. To our surprise, one dimensional (1D) distributed feedback lasers based on PFP-3 with long flexible side chains as gain media achieved quite low pump energy thresholds (0.28 KW/cm2) with a wavelength ranging from 456.0 nm to 471.4 nm. R1

R2

PFP-1

R1=H

R2=CH3

PFP-2

R1=CH3

R2=CH3

PFP-3

R1=OC6H13

R2=OC6H13

PFP-4

R1=OC6H12(C2H5)

R2=OC6H12(C2H5)

Scheme 1. Molecular structures of PFP-X, X = 1-4. RESULTS AND DISCUSSION Synthesis and physical properties. The synthetic routes toward the pyrenyl-capped benzofiurene derivatives, PFP-1, PFP-2, PFP-3 and PFP-4, are depicted in Scheme 2. Compound 1 was obtained by reacting 2,7-dibromo-fluorenone with the Grignard reagent of 4-bromotoluene, then dehydrated to give compound 1 with the aid of acids. The synthetic route to obtain compound 2 was similar to that of compound 1, except for the use of toluene for the dehydration reaction. 5 ACS Paragon Plus Environment


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2,7-Dibromo-fluorenone

was

treated

with

phenol

and

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methanesulfonic

acid,

yielding

2,7-dibromo-9,9-bis-(4-hydroxy-phenyl)-fluorene. Compound 3 and 4 were obtained by reacting the different alkoxy phenyl-substituted fluorene segments with 1-bromohexane and 2-ethylhexyl bromide, respectively. Microwave-assisted multiple Suzuki coupling reactions37-40 of pyrene boric acid with compounds 1, 2, 3, and 4 were employed for the synthesis of PFP-1, PFP-2, PFP-3, and PFP-4, respectively. The purity and chemical structures of PFP-1, PFP-2, PFP-3, and PFP-4 were well confirmed by 1H NMR,

13

C NMR and MALDI-TOF mass spectrometry, as shown in Fig.

S1-S12 (Supporting Information).

c Br

Br

OH

1

Br

Br d

a

Br

Br

O Br

2

Br C6H 13O

OC 6H13

Br

Br

e b HO

OH 3

Br

Br O

O

f Br

Br 4

O BO

PFP-1, PFP-2, PFP-3, PFP-4

1, 2, 3, 4 Microwave, pressurized vessel, Pd(pph3) 4, K2CO3, THF, 150℃, 30 min

Scheme 2. Reagents and conditions: (a) (1) 4-bromotoluene, Mg, I2, THF, (2) 2, 6 ACS Paragon Plus Environment

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7-dibromofluorenone, THF, reflux; (b) phenol, 3-methanesulfonic acid, CH3SO3H, 50°C, 16 h; (c) benzene, CH3SO3H, 140°C, reflux; (d) toluene, CH3SO3H, 140°C, reflux; (e) 1-bromohexane, K2CO3, DMF, 70°C, 24 h; (f) 2-ethylhexyl bromide, K2CO3, DMF, 70°C, 24 h. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) measurements were carried out to investigate the impact of flexible side chains on their thermal properties. The results are shown in Fig. 1 and summarized in Table 1. All the compounds are thermally stable with 5% weight loss temperature (Td) over 435°C, ensuring their good thermal stabilities to be used as active materials for optoelectronic applications. As revealed by DSC curves, PFP-1 and PFP-2 are stable amorphous materials with glass transition temperature (Tg) of 175°C and 168°C, respectively. In contrast, PFP-3 and PFP-4 show lower Tg values of 113°C and 84°C, respectively, probably resulting from the introduction of long flexible side chains. These results manifest that Tg values of PFP-X decrease with increasing the flexible chain length on diaryl substituents at C9 position of the fluorene units.

PFP-1 PFP-2 PFP-3 PFP-4

100

PFP-2

PFP-1

Weight (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


80

60

Tg=175 oC

160 170 PFP-3

Tg=168 oC

180 120

150

180

PFP-4 Tg=84 oC

Tg=113 oC 85

40 100

105

200

125 60

300

80

100

400

500

600

700

o

Temperature ( C) Fig. 1. TGA and DSC curves of PFP-X at a heating rate of 10°C min-1. 7 ACS Paragon Plus Environment


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The powder wide-angle X-ray diffraction (WAXRD) patterns of PFP-X are shown in Fig. S13. For PFP-1 and PFP-2, a series of sharp diffraction peaks were recorded with high intensity, which are suggestive of the crystalline nature of the rigid conjugated molecular backbone. Both PFP-3 and PFP-4 exhibited similar weak and broad amorphous peaks, suggesting their amorphous glassy morphologies. These results testify that an increase in the lengths of flexible chain substituents can effectively depress the crystalline nature of the rigid conjugated molecular backbone to achieve amorphous properties.

Fig. 2. AFM topographic images of (a) PFP-1, (b) PFP-2, (c) PFP-3 and (d) PFP-4.

Atomic force microscopy (AFM) measurements were conducted from the pristine films of PFP-X on spectrosil substrates to explore the influence of flexible side chains on the morphology 8 ACS Paragon Plus Environment

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and the film-forming ability, as shown in Fig. 2a-d. The films were spin-coated from toluene solution and then heated at 60°C for 1 h to remove the solvent. An extremely rough surface was recorded with a root-mean-square (RMS) roughness of 3.90 nm for PFP-1 and 3.95 nm for PFP-2, respectively, which was mainly ascribed to their high crystallinity. The trends were consistent with the XRD analysis. Generally speaking, such poor film-forming ability is not desirable for organic semiconductor devices. In contrast, the films of PFP-3 and PFP-4 exhibited a smooth and uniform surface with the RMS roughness of 0.38 nm and 0.40 nm, respectively. These results suggested that the modulation of flexible chain length on diaryl substituents could effectively improve their amorphous properties and film-forming ability, therefore largely facilitating the fabrication of homogeneous amorphous thin films by solution processing, which is highly demanded for organic optoelectronic devices. Photophysical and electrochemical properties. The UV-Vis absorption and photoluminescence (PL) spectra of PFP-X in solution and in films are shown in Fig. 3. The relevant data are summarized in Table 1. The absorption spectra of the four compounds in dilute solution (Fig. 3a) exhibit a broad absorption band with no obvious vibrational features. Meanwhile, their nearly identical absorption spectra of PFP-X in both solution and solid states imply that the conjugated backbone rather than the flexible side chains dominates the absorption properties in the ground states, indicating no formation of any distinct aggregates for this rigid conjugated π system when going from dilute solution to thin film condensed states. As shown in Fig. 3b, the PL spectra of PFP-3 and PFP-4 in solution manifest almost the same peak at 432 nm, showing a slight red-shift compared with those of PFP-1 and PFP-2 at 426 nm. Under this circumstance, it can be construed that the alkoxyl benzene as a weak electron-donating 9 ACS Paragon Plus Environment


groups in PFP-3 and PFP-4 could lead to additional intramolecular energy transfer and red-shifted radiative decay.41 The PL spectra of the PFP-X films are red-shifted by about 40 nm in comparison to those recorded from the dilute solutions, suggesting obvious intermolecular interactions in the excited states, i.e. excimer formation. Furthermore, the PL spectra of PFP-3 and PFP-4 show a narrowed, and red-shifted emission, compared with those obtained from PFP-1 and PFP-2. The narrower emission band might be due to more efficient energy transfer through exciton migration42 for PFP-3 and PFP-4. This hypothesis also fits the fluorescence lifetimes data (see Fig. 4b). (a)

(b) N orm alized Photolum inescence (a. u.)

PFP-1-Solution PFP-2-Solution PFP-3-Solution PFP-4-Solution

Norm alized Absorbance (a. u.)

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PFP-1-Film PFP-2-Film PFP-3-Film PFP-4-Film

300

350

400

450

500

PFP-1-Solution PFP-2-Solution PFP-3-Solution PFP-4-Solution

PFP-1-Film PFP-2-Film PFP-3-Film PFP-4-Film

400

Wavelength (nm)

450

500

550

600

Wavelength (nm)

Fig. 3. (a) Normalized UV-visible absorption spectra of PFP-X in THF solution (10-6 mol/L) and film states. (b) Normalized PL spectra of PFP-X in THF solution (10-6 mol/L) and film states. The photoluminescence quantum yields (PLQY) of the samples in films were estimated to be 28%, 30%, 46%, and 38% for PFP-1, PFP-2, PFP-3 and PFP-4, respectively, measured on quartz plates using an intergrating sphere. Photophysical data of PFP-X are listed in Table 1. These features clearly corroborate that the flexible side chains may play an important role on impacting the process of exciton migration and exciton annihilation in the solid states, further resulting in distinct different emissive behaviours. 10 ACS Paragon Plus Environment

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To gain an insight into the excited state relaxation processes of the samples and to determine the governing relaxation pathway, fluorescence transients of PFP-1, PFP-2, PFP-3 and PFP-4 were investigated. The transients measured at the fluorescence band maxima of the studied samples in 10-5 M THF solution and neat films are presented in Fig. 4a and Fig. 4b, respectively. Excited state relaxation of the compounds in solution was found to follow a quite similar single exponential decay profile with estimated fluorescence lifetimes (τ) of 1.22-1.26 ns for PFP-X with a deviation of only 0.04 ns. Comparing with the pyrene chromophore, the estimated lifetimes are 2 orders of magnitude shorter, suggesting much more efficient and fast decay from the lowest S1→S0 transition for PFP-X in dilute solution.43 As a consequence, the different flexible chain lengths on diaryl substituents have little influence on the decay time of molecules in dilute solutions. Table 1. Photophysical data of PFP-X ( X=1, 2, 3, 4). Estimated fluorescence lifetimes

Compd

Td[a] [°C]

Tg[b] [°C]

λmax,abs [nm]

λmax, PL [nm]

PLQY [e]

τsolution [ns]

τfilm [ns]

PFP-1

510

175

363[c]/372[d]

426[c]/460[d]

28%

1.22

1.81 (54%), 7.27 (46%)

PFP-2

508

168

363[c]/369[d]

424[c]/464[d]

30%

1.26

1.38 (47%), 6.65 (54%)

PFP-3

443

113

368[c]/370[d]

432[c]/472[d]

46%

1.22

2.61 (33%), 9.13 (67%)

PFP-4

439

84

364[c]/373[d]

432[c]/473[d]

38%

1.24

2.68 (33%), 9.83 (67%)

[a]

Td: decomposition temperature. [b] Tg: glass transition temperature. [c] Measured in THF solution. [d]

Measured in films. [e] PLQY in films, measured on quartz plates using an integrating sphere. The influence of flexible side chains become more pronounced in neat films for PFP-X as shown in Fig. 4b. The relaxation decays of the samples in neat films was found to follow a bi-exponential decay profile with estimated fluorescence lifetimes of τ1 (PFP-1) = 1.81 ns (54%) and τ2 (PFP-1) = 7.27 ns (46%) for PFP-1, τ1 (PFP-2) = 1.38 ns (47%) and τ2 (PFP-2) = 6.65 ns (53%) for PFP-2, τ1 11 ACS Paragon Plus Environment


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(PFP-3) = 2.61 ns (33%) and τ2 (PFP-3) = 9.13 ns (67%) for PFP-3, τ1 (PFP-4) = 2.68 ns (33%) and τ2 (PFP-4) = 9.83 ns (67%) for PFP-4, respectively. The average lifetime of PFP-X in films are 4.32 ns, 4.24 ns, 6.98 ns, 7.47 ns, respectively. Meanwhile, the shorter τ1 of PFP-X in films are close to those in solutions. The τ1 is thus ascribed to exciton migration, and then the migration-induced exciton quenching. The prolonged relaxation (τ2) is attributed to the excimer-like states, where the excitons localize at lower energy levels.44 The bi-exponential transients with rapid excited state relaxation in an early stage (ca. 1-3 ns after excitation) and prolonged relaxation at a later stage (ca. 6 ns after excitation) are typically observed in solid states, where exciton localization at lower energy levels take place.45 During the initial exciton migration stage, migration-induced exciton quenching at nonradiative decay centers occurs, which drastically degrades PLQY of the neat films. Being localized at lower energy states, excitons evade fast radiative decay and therefore, exhibit prolonged relaxation times. Furthermore, there is a much smaller fast decay component in PFP-3 and PFP-4 compared with PFP-1 and PFP-2 in film states, which suggests that there is efficient migration of the excitations to the excimer-like states.46 Obviously, the long flexible side chains in PFP-3 and PFP-4 causes more pronounced excition migration in excimer-like states and, thus efficient energy transfer, comparing with PFP-1 and PFP-2. This hypothesis has also been confirmed by the lower PLQY values of PFP-1 and PFP-2 in comparison to those of PFP-3 and PFP4 in film states. Obviously, the long flexible chains are beneficial for mitigating the exciton annihilation and retaining the emissive properties of the samples in film states. To further understand the electronic properties of PFP-X, the electrochemical behaviours of the samples were investigated by cyclic voltammetry (CV). The measurements were carried out with a standard

three

electrodes

electrochemical

cell

in

a

0.1


M

tetra-n-butylammomium

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hexafluorophosphate (Bu4NPF6) in CH2Cl2 at room temperature under nitrogen with a scanning rate of 100 mV/s. The oxidation onset potentials are measured to be 0.85, 0.90, 0.95 and 1.18 V for PFP-1, PFP-2, PFP-3, and PFP-4, respectively. The corresponding HOMO energy levels are thus estimated to be -5.62, -5.67, -5.72 and -5.95 eV for PFP-1, PFP-2, PFP-3, and PFP-4, respectively. The LUMO values of PFP-1, PFP-2, PFP-3, and PFP-4 are quite similar ranging from -2.54 eV to -2.57 eV, which are estimated from the onset reduction potentials assuming the absolute energy level of Fc/Fc+ to be 4.8 eV below vacuum (Table S1 and Fig. S14).47 (a)

(b)

PFP-1-Solution, τ=1.22 ns PFP-2-Solution, τ=1.24 ns PFP-3-Solution, τ=1.22 ns PFP-4-Solution, τ=1.26 ns

0.1

0.01

0

10

20 30 Time (ns)

40

PFP-1-Solution PFP-1-Film, =4.32 ns PFP-2-Film, =4.24 ns PFP-3-Film, =6.98 ns PFP-4-Film, =7.47 ns

1 Norm. Intensity (a. u.)

1 Norm. Intensity (a. u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


50

0.1

0.01

0

20 40 Time (ns)

60

Fig. 4. Fluorescence transients of (a) THF solution (10-5 M) and (b) films of PFP-X measured at the fluorescence band maxima. Theoretical Calculations. The photophysical characteristics of organic emitters mainly depend on their ground- and excited-state properties, which can be simulated via quantum chemical calculations. Quantum chemical calculations of the pyrenyl-capped benzofiurene derivatives were performed using density functional theory (DFT) method as implemented in Gaussian 03 software package. Ground-state geometries of the molecular structures were optimized at the B3LYP functional level with the 6-31G (d, p) basis set supplemented with polarization functions. By means of the semi-empirical ZINDO calculations, singlet transition energies and spatial distributions of electron density for HOMO (0, -1, -2) and LUMO (0, +1, +2) were acquired. 13 ACS Paragon Plus Environment


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To get insight into how the different flexible chain length on diaryl substituents influences the electronic structures and energy levels, the optimization was performed by inspecting the first few HOMOs (HOMO to HOMO-2) and LUMOs (LUMO to LUMO+2) of the four samples (Fig. 5). The HOMO, LUMO, and LUMO+2 of the parent compounds (PFP-1/2/3/4) are mainly localized on the molecular backbone, while the HOMO-1, LUMO+1 primarily arise from the pyrene units. For PFP-1 and PFP-2, all the HOMOs and LUMOs are mainly localized on the molecular backbone and correlate to frontier molecular orbitals (MOs) of the molecular backbone itself, indicating limited interaction between the central chromophore and the peripheral flexible side chain substitutions. Although HOMO and HOMO-1 in PFP-3 and PFP-4 are also mostly on the backbone, there is a relatively significant difference of HOMO-2 onto the substitution due to MO is made up of the energetically close alkoxy benzene HOMO. The HOMO-2 MOs in PFP-3 and PFP-4 may enhance the participation of π-π orbital interactions between the diaryl substituents and conjugated backbones, which would help to change the excitation and radiative deactivation pathways.48-50 Overall, the flexible side chains exhibit notable electronic couplings with the molecular backbone, depending on the characteristics of substitutions (e.g., MO levels of the substitution, the way of linkage, etc.). Despite a slight change, the configuration of PFP-1 and PFP-2 results in close HOMO and HOMO-1 as well as LUMO and LUMO+1, which is beneficial for the intermolecular charge transfer compared with PFP-3 and PFP-4.51 The results show that the flexible side chain substitutions have relatively significant influences on the electronic structures of the resulting samples, and thus affecting the photophysical properties and device performance. With the aim to better understand how different flexible chain length on diaryl substituents affects the molecular architecture, dihedral angles between pyrene and fluorene (D1) and between 14 ACS Paragon Plus Environment

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fluorene and benzene (D2 and D3) (see Fig. S15 and Table S2) are systematically measured. On the basis of the results, dihedral angels (D1, D2, D3) in our system are similar, indicating that the different flexible chain length on diaryl substituents have little impact on the molecular architecture, which is much different from the molecular systems based on D-π-A backbones.52-55

Fig. 5. Energy level diagrams, molecular configuration and frontier molecular orbitals of PFP-X, simulated by DFT calculations. Electroluminescent Properties. Owing to their good solubility and film-forming properties, the electroluminescent properties of solution-processed PFP-3 and PFP-4 were studied. Nondoped OLED devices based on the two samples were fabricated in the configuration ITO/PEDOT:PSS (40 nm)/PFP-3 or PFP-4 (50 nm)/TPBI (40 nm) /LiF (0.5 nm)/Al (80 nm) (Device 1/2), where TPBI was used as a buffer electron-transporting and hole-blocking layer.



(b) 3.0

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Device 1 CIE=(0.15, 0.15) Device 2 CIE=(0.15, 0.13) Device 6 CIE=(0.15, 0.08) Device 11 CIE=(0.16, 0.07)

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Fig. 6. (a) Current density-voltage-brightness (J-V-L) characteristics for Device 1 and 2. (b) Current efficiency-luminance-power efficiency characteristics of Devices 1 and 2. (c) Normalized EL spectra of Device 1 at various driving voltages. (d) Normalized EL spectra of Device 1, 2, 6, and 10 at 8 V. Device 1 exhibited a low turn-on voltage of 3.75 V, the maximum luminance of 8372 cd/m2 at 8.3 V, the current density of 470 mA/cm2, the maximum efficiency of 2.56 cd/A, and the CIE coordinates of (0.15, 0.15) (Fig. 6a, 6b, 6d). It is noteworthy to mention that the device still keeps a considerable efficiency of 1.78 cd/A, when the luminescence reaches its maximum. This implies that the device is quite stable against various working conditions before damage. With increasing driving voltage from 4 to 8 V, the EL spectra of Device 1 remain nearly unchanged, and the CIE coordinate values show negligible variation, suggesting a remarkable bias-independent EL emission 16 ACS Paragon Plus Environment

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(Fig. 6c). Furthermore, the EL spectra of these materials (PFP-3 or PFP-4) are similar to their PL spectra in thin film states, indicating no additional formation of excimer or exciplex during the EL process.56-57 Due to their poor film-forming properties it was not possible to fabricate OLEDs based on PFP-1 and PFP-2 neat films by solution processing. 4, 4’-Bis(9H-carbazol-9-yl) biphenyl (CBP) was used as a host to fabricate OLED devices doped with PFP-1 or PFP-2 with various concentrations of 4%, 6%, 8%, 10%, 12%. Among these doped devices, the highest performance was achieved at 10 wt%. As summarized in Table S3, performances of doped devices (Device 3-12) based on PFP-1 and PFP-2 are inferior to those of the nondoped devices (Device 1 and 2) based on PFP-3 and PFP-4 in terms of the turn-on voltage, maximum current efficiency, maximum brightness and maximum power efficiency, although some of the doped devices achieved better color purity (Fig. 6d). Amplified Spontaneous Emission (ASE) and Lasing Properties. Organic emitters with good thermal and morphological stabilities are promising for organic solid-state lasers.58-62 To explore the potential of the resulting materials for optical gain applications, PFP-3 and PFP-4 were selected as the samples to investigate the lasing properties because of their good solubility and better film-forming properties. The ASE and lasing emission measurements of PFP-3 and PFP-4 were carried out in a slab waveguide structure with a 375 nm excitation laser source (10 Hz, 5 ns pulsed excitation from a Nd:YAG laser pumped optical parametric amplifier). The representative UV, PL, amplified spontaneous emission (ASE) spectra for PFP-3 and PFP-4 films on silica substrates are shown in Fig. 7a and the thicknesses of the corresponding films in these measurements are approximate 125 nm for PFP-3 and 120 nm for PFP-4, respectively. Increasing the excitation energy per pulse results in narrowing the PL spectra with peaks at 454 17 ACS Paragon Plus Environment


nm and 450 nm for PFP-3 and PFP-4, respectively. A threshold pulse energy Eth is defined at which the full width at half maximum indensity (FWHM) of the emission spectrum drops to half of its low intensity excitation PL value.63 An alternative threshold energy measure comes from the observation of a kink in the output versus input intensity (Iout vs. Iin) characteristics (Fig. 7b). The ASE threshold (Eth) values are 22.75 µJ/cm2 (0.41 µJ/pulse) and 32.45 µJ/cm2 (0.58 µJ/pulse) at 25 °C for PFP-3 and PFP-4, respectively. Fig. 7a shows the ASE spectra of PFP-3 and PFP-4, in which the FWHM has reduced to 8.7 nm and 8.5 nm, from the ca. 95 nm linewidth characteristic of the normal PL spectrum, respectively (Fig. S16 and S17).

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1.0 0.8 0.6 0.4

PFP-3 PFP-4

0.2 0.0 0

50

100

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Fig. 7. (a) UV, PL and ASE spectra of compound PFP-3 and PFP-4 collected on thick films. The films were spin-cast from a 30 mg/mL toluene solution, and the thickness was controlled by the spinning speed. Excitation wavelength: 370 nm and 373 nm for PL; 375 nm for ASE. (b) Normalized output intensity versus pump energy for PFP-3 and PFP-4. PFP-3 was selected to investigate the gain properties because of its highest PLQY, the lower ASE threshold and better OLED performance. Optically pumped surface-emitting distributed feedback (DFB) lasers were fabricated. Resonant feedback in DFB structures was introduced by spin-coating the films onto gratings patterned into silica substrates. By using a 280 nm period, 50% 18 ACS Paragon Plus Environment

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fill factor and 80 nm depth 1D grating and varying the film thickness from 280 nm to 300 nm, we were able to tune the lasing wavelength over a range of at least 15 nm (456.0 nm to 471.4 nm) in the blue emission with the lowest lasing threshold of 0.28 KW/cm2 at 456.0 nm (Fig. 8), which are comparable and even better than most of the results reported for organic lasers in the literature.58-59, 63-64

The FWHM-Pump energy-output intensity characteristics for the 456.0 nm and 460.0 nm are

presented in Fig. S18 and Fig. S19.

Normalized Intensity (a. u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


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Fig. 8. The lasing spectra obtained by tuning the film thickness. The peaks are observed at 456.0 nm, 460.0 nm, 468.2 nm, 471.4 nm, corresponding to the film thickness of 280 nm, 290 nm, 300 nm and 310 nm, respectively. CONCLUSIONS In summary, a new series of pyrenyl-capped derivatives (PFP-X) have been synthesized in high yields by microwave-assisted multiple Suzuki reaction and explored as ideal model samples to investigate the impacts of flexible side chains on the functional optoelectronic properties. The resulting samples manifest good thermal stability and high fluorescence yields. A combination of UV/PL spectra, AFM images, XRD patterns, fluorescence transients and quantum chemical calculations has offered an opportunity to explore how flexible side chains influence the electronic 19 ACS Paragon Plus Environment


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structure, intermolecular interactions and exciton quenching, resulting in various photophysical and electrochemical behaviours, and further affecting the device performance. The increase of flexible chain lengths can effectively reduce the intermolecular interactions and depress the crystalline nature, leading to improved morphology properties and prominent optoelectronic characteristics. The nondoped solution-processed blue OLEDs using PFP-3 and PFP-4 have maximum current efficiencies of 2.56 and 2.35 cd/A with CIE coordinates of (0.15, 0.15) and (0.15, 0.13), respectively, which realized high-efficiency performance comparable to vaccum-deposited devices. In addition, 1D distributed feedback lasers using PFP-3 as gain media have demonstrated a wavelength ranging from 456.0 nm to 471.4 nm and low pump energy thresholds (0.28 KW/cm2), which is among the best results ever reported for organic laser gain media. This study emphasizes that subtle structural alteration even for flexible side chains can significantly affect the corresponding characteristics, which are vital for rational design of the molecular structures for optoelectronic applications. ASSOCIATED CONTENT

Supporting Information

Synthetic procedures; chemical and photophysical results (including NMR, MALDI-TOF, AFM, PLQY and PL decay) of PFP-X samples; WAXD patterns of PFP-X powders; cyclic voltammograms of PFP-X films; DFT-calculated molecular structures and several dihedral angels of PFP-X; ASE parameters of PFP-3 and PFP-4, including ASE peak, FWHM and ASE output intensity changing with pump energy; 1D DFB laser characteristics of PFP-3; general methods for OLED device fabrication, the ASE and laser characterization. This information is available free of charge via the Internet at http://pubs.acs.org. 20 ACS Paragon Plus Environment

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AUTHOR INFORMATION Corresponding Author *Email: [email protected] (W. Y. Lai); [email protected] (W. Huang); Tel/Fax: +86 25 8586 6008.

Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

Notes The authors declare no competing financial interest.

Acknowledgment The authors acknowledge financial support from the National Key Basic Research Program of China (973 Program, 2014CB648300), the National Natural Science Foundation of China (21422402, 20904024, 51173081, 61136003), the Natural Science Foundation of Jiangsu Province (BK20140060, BK20130037, BM2012010), Program for Jiangsu Specially-Appointed Professors (RK030STP15001), Program for New Century Excellent Talents in University (NCET-13-0872), Specialized Research Fund for the Doctoral Program of Higher Education (20133223110008, and 20113223110005), the Ministry of Education of China (IRT1148), the Synergetic Innovation Center for Organic Electronics and Information Displays, the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD), the NUPT "1311 Project", the Six Talent Plan (2012XCL035), the 333 Project (BRA2015374) and the Qing Lan Project of Jiangsu Province. REFERENCES 21 ACS Paragon Plus Environment


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(1) Qin, T.; Wiedemair, W.; Nau, S.; Trattnig, R.; Sax, S.; Winkler, S.; Vollmer, A.; Koch, N.; Baumgarten, M.; List, E. J. W.; et al. Core, Shell, and Surface-Optimized Dendrimers for Blue Light-Emitting Diodes. J. Am. Chem. Soc. 2011, 133, 1301-1303. (2) Luo, J.; Zhou, Y.; Niu, Z.-Q.; Zhou, Q.-F.; Ma, Y.; Pei, J. Three-Dimensional Architectures for Highly Stable Pure Blue Emission. J. Am. Chem. Soc. 2007, 129, 11314-11315. (3) Nau, S.; Schulte, N.; Winkler, S.; Frisch, J.; Vollmer, A.; Koch, N.; Sax, S.; List, E. J. W. Highly Efficient Color-Stable Deep-Blue Multilayer PLEDs: Preventing PEDOT:PSS-Induced Interface Degradation. Adv. Mater. 2013, 25, 4420-4424. (4) Wang, N.; Chen, Z.; Wei, W.; Jiang, Z. Fluorinated Benzothiadiazole-Based Conjugated Polymers for High-Performance Polymer Solar Cells without Any Processing Additives or Post-Treatments. J. Am. Chem. Soc. 2013, 135, 17060-17068. (5) Qin, T.; Zajaczkowski, W.; Pisula, W.; Baumgarten, M.; Chen, M.; Gao, M.; Wilson, G.; Easton, C. D.; Muellen, K.; Watkins, S. E. Tailored Donor-Acceptor Polymers with an A-D1-A-D2 Structure: Controlling Intermolecular Interactions to Enable Enhanced Polymer Photovoltaic Devices. J. Am. Chem. Soc. 2014, 136, 6049-6055. (6) He, Z.; Xiao, B.; Liu, F.; Wu, H.; Yang, Y.; Xiao, S.; Wang, C.; Russell, T. P.; Cao, Y. Single-Junction Polymer Solar Cells with High Efficiency and Photovoltage. Nat. Photonics 2015, 9, 174-179. (7) He, Z.; Zhong, C.; Su, S.; Xu, M.; Wu, H.; Cao, Y. Enhanced Power-Conversion Efficiency in Polymer Solar Cells Using an Inverted Device Structure. Nat. Photonics 2012, 6, 591-595. (8) Amin, A. Y.; Khassanov, A.; Reuter, K.; Meyer-Friedrichsen, T.; Halik, M. Low-Voltage Organic Field

Effect

Transistors

with

a

2-Tridecyl[1]benzothieno[3,2-b][1]benzothiophene

Semiconductor Layer. J. Am. Chem. Soc. 2012, 134, 16548-16550. 22 ACS Paragon Plus Environment

Page 22 of 31

Page 23 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(9) Lei, T.; Dou, J.-H.; Pei, J. Influence of Alkyl Chain Branching Positions on the Hole Mobilities of Polymer Thin-Film Transistors. Adv. Mater. 2012, 24, 6457-6461. (10) Giri, G.; Verploegen, E.; Mannsfeld, S. C. B.; Atahan-Evrenk, S.; Kim, D. H.; Lee, S. Y.; Becerril, H. A.; Aspuru-Guzik, A.; Toney, M. F.; Bao, Z. Tuning Charge Transport in Solution-Sheared Organic Semiconductors Using Lattice Strain. Nature 2011, 480, 504-508. (11) Tsao, H. N.; Cho, D. M.; Park, I.; Hansen, M. R.; Mavrinskiy, A.; Yoon, D. Y.; Graf, R.; Pisula, W.; Spiess, H. W.; Muellen, K. Ultrahigh Mobility in Polymer Field-Effect Transistors by Design. J. Am. Chem. Soc. 2011, 133, 2605-2612. (12) Lei, T.; Cao, Y.; Fan, Y.; Liu, C.-J.; Yuan, S.-C.; Pei, J. High-Performance Air-Stable Organic Field-Effect Transistors: Isoindigo-Based Conjugated Polymers. J. Am. Chem. Soc. 2011, 133, 6099-6101. (13) Wang, C.; Zhang, J.; Long, G.; Aratani, N.; Yamada, H.; Zhao, Y.; Zhang, Q. Synthesis, Structure, and Air-stable N-type Field-Effect Transistor Behaviors of Functionalized Octaazanonacene-8,19-dione. Angew. Chem. Int. Edit. 2015, 54, 6292-6296. (14) Chen, W.; Zhang, J.; Long, G.; Liu, Y.; Zhang, Q. From Non-Detectable to Decent: Replacement of Oxygen with Sulfur in Naphthalene Diimide Boosts Electron Transport in Organic Thin-Film Transistors (OTFT). J. Mater. Chem. C 2015, 3, 8219-8224. (15) Wu, J.-S.; Cheng, S.-W.; Cheng, Y.-J.; Hsu, C.-S. Donor-Acceptor Conjugated Polymers Based on Multifused Ladder-Type Arenes for Organic Solar Cells. Chem. Soc. Rev. 2015, 44, 1113-1154. (16) Zhu, M.; Yang, C. Blue Fluorescent Emitters: Design Tactics and Applications in Organic Light-Emitting Diodes. Chem. Soc. Rev. 2013, 42, 4963-4976. (17) Mei, J.; Kim, D. H.; Ayzner, A. L.; Toney, M. F.; Bao, Z. Siloxane-Terminated Solubilizing 23 ACS Paragon Plus Environment


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Side Chains: Bringing Conjugated Polymer Backbones Closer and Boosting Hole Mobilities in Thin-Film Transistors. J. Am. Chem. Soc. 2011, 133, 20130-20133. (18) Osaka, I.; Zhang, R.; Sauve, G.; Smilgies, D.-M.; Kowalewski, T.; McCullough, R. D. High-Lamellar

Ordering

and

Amorphous-Like

π-Network

in

Short-Chain

Thiazolothiazole-Thiophene Copolymers Lead to High Mobilities. J. Am. Chem. Soc. 2009, 131, 2521-2529. (19) Chen, H.; Guo, Y.; Yu, G.; Zhao, Y.; Zhang, J.; Gao, D.; Liu, H.; Liu, Y. Highly π-Extended Copolymers with Diketopyrrolopyrrole Moieties for High-Performance Field-Effect Transistors. Adv. Mater. 2012, 24, 4618-4622. (20) Pertegas, A.; Tordera, D.; Serrano-Perez, J. J.; Orti, E.; Bolink, H. J. Light-Emitting Electrochemical Cells Using Cyanine Dyes as the Active Components. J. Am. Chem. Soc. 2013, 135, 18008-18011. (21) Kim, H.; Schulte, N.; Zhou, G.; Muellen, K.; Laquai, F. A High Gain and High Charge Carrier Mobility Indenofluorene-Phenanthrene Copolymer for Light Amplification and Organic Lasing. Adv. Mater. 2011, 23, 894-897. (22) Oosterbaan, W. D.; Bolsee, J.-C.; Gadisa, A.; Vrindts, V.; Bertho, S.; D'Haen, J.; Cleij, T. J.; Lutsen, L.; McNeill, C. R.; Thomsen, L.; et al. Alkyl-Chain-Length-Independent Hole Mobility via Morphological Control with Poly(3-alkylthiophene) Nanofibers. Adv. Funct. Mater. 2010, 20, 792-802. (23) Szarko, J. M.; Guo, J.; Liang, Y.; Lee, B.; Rolczynski, B. S.; Strzalka, J.; Xu, T.; Loser, S.; Marks, T. J.; Yu, L.; et al. When Function Follows Form: Effects of Donor Copolymer Side Chains on Film Morphology and BHJ Solar Cell Performance. Adv. Mater. 2010, 22, 5468-5472. 24 ACS Paragon Plus Environment

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(24) Piliego, C.; Holcombe, T. W.; Douglas, J. D.; Woo, C. H.; Beaujuge, P. M.; Frechet, J. M. J. Synthetic Control of Structural Order in N-Alkylthieno[3,4-c]pyrrole-4,6-dione-Based Polymers for Efficient Solar Cells. J. Am. Chem. Soc. 2010, 132, 7595-7597. (25) Cho, E.; Risko, C.; Kim, D.; Gysel, R.; Miller, N. C.; Breiby, D. W.; McGehee, M. D.; Toney, M. F.; Kline, R. J.; Bredas, J.-L. Three-Dimensional Packing Structure and Electronic Properties of Biaxially Oriented Poly(2,5-bis(3-alkylthiophene-2-yl)thieno-[3,2-b]thiophene) Films. J. Am. Chem. Soc. 2012, 134, 6177-6190. (26) Yiu, A. T.; Beaujuge, P. M.; Lee, O. P.; Woo, C. H.; Toney, M. F.; Frechet, J. M. J. Side-Chain Tunability of Furan-Containing Low-Band-Gap Polymers Provides Control of Structural Order in Efficient Solar Cells. J. Am. Chem. Soc. 2012, 134, 2180-2185. (27) Wu, Y.-S.; Li, J.; Ai, X.-C.; Fu, L.-M.; Zhang, J.-P.; Fu, Y.-Q.; Zhou, J.-J.; Li, L.; Bo, Z.-S. Interplay Between the Keto Defect and the Interchain Interaction on the Green Emission of Fluorene-Based Polymer. J. Phys. Chem. A 2007, 111, 11473-11479. (28) Becker, K.; Lupton, J. M.; Feldmann, J.; Nehls, B. S.; Galbrecht, F.; Gao, D. Q.; Scherf, U. On-Chain Fluorenone Defect Emission from Single Polyfluorene Molecules in the Absence of Intermolecular Interactions. Adv. Funct. Mater. 2006, 16, 364-370. (29) Sims, M.; Bradley, D. D. C.; Ariu, M.; Koeberg, M.; Asimakis, A.; Grell, M.; Lidzey, D. G. Understanding the Origin of the 535 nm Emission Band in Oxidized Poly(9,9-dioctylfluorene): The Essential Role of Inter-Chain/Inter-Segment Interactions. Adv. Funct. Mater. 2004, 14, 765-781. (30) Kappaun, S.; Scheiber, H.; Trattnig, R.; Zojer, E.; List, E. J. W.; Slugovc, C. Defect Chemistry of Polyfluorenes: Identification of the Origin of "Interface Defects" in Polyfluorene Based Light-Emitting Devices. Chem. Commun. 2008, 41, 5170-5172. 25 ACS Paragon Plus Environment


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(31) Figueira-Duarte, T. M.; Muellen, K. Pyrene-Based Materials for Organic Electronics. Chem. Rev. 2011, 111, 7260-7314. (32) Tao, S. L.; Peng, Z. K.; Zhang, X. H.; Wang, P. F.; Lee, C. S.; Lee, S. T. Highly Efficient Non-Doped Blue Organic Light-Emitting Diodes based on Fluorene Derivatives with High Thermal Stability. Adv. Funct. Mater. 2005, 15, 1716-1721. (33) Tang, C.; Liu, F.; Xia, Y. J.; Lin, J.; Xie, L. H.; Zhong, G. Y.; Fan, Q. L.; Huang, W. Fluorene-Substituted Pyrenes-Novel Pyrene Derivatives as Emitters in Nondoped Blue OLEDs. Org. Electron. 2006, 7, 155-162. (34) Liu, F.; Tang, C.; Chen, Q.-Q.; Shi, F.-F.; Wu, H.-B.; Xie, L.-H.; Peng, B.; Wei, W.; Cao, Y.; Huang, W. Supramolecular π-π Stacking Pyrene-Functioned Fluorenes: Toward Efficient Solution-Processable Small Molecule Blue and White Organic Light Emitting Diodes. J. Phys. Chem.

C 2009, 113, 4641-4647.

(35) Tang, C.; Xu, H.; Liu, F.; Xia, Y.-J.; Huang, W. Isolated Large πSystems in Pyrene-Fluorene Derivatives for Intramolecular Through-Space Interaction in Organic Semiconductors. Org. Electron. 2013, 14, 782-789. (36) Liu, F.; Tang, C.; Chen, Q.-Q.; Li, S.-Z.; Wu, H.-B.; Xie, L.-H.; Peng, B.; Wei, W.; Cao, Y.; Huang, W. Pyrene Functioned Diarylfluorenes as Efficient Solution Processable Light Emitting Molecular Glass. Org. Electron. 2009, 10, 256-265. (37) Lai, W.-Y.; Chen, Q. Q.; He, Q. Y.; Fan, Q. L.; Huang, W. Microwave-Enhanced Multiple Suzuki Couplings Toward Highly Luminescent Starburst Monodisperse Macromolecules. Chem. Commun. 2006, 18, 1959-1961. (38) Lai, W.-Y.; Zhu, R.; Fan, Q. L.; Hou, L. T.; Cao, Y.; Huang, W. Monodisperse Six-Armed Triazatruxenes: Microwave-Enhanced Synthesis and Highly Efficient Pure-Deep-Blue 26 ACS Paragon Plus Environment

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Electroluminescence. Macromolecules 2006, 39, 3707-3709. (39) Lai, W.-Y.; Liu, D.; Huang, W. Towards Highly Substituted Starburst Macromolecular Semiconductors: Microwave Synthesis, Spectroscopy and Electrochemical Properties. Macromol. Chem. Phys. 2011, 212, 445-454. (40) Lai, W.-Y.; Xia, R.; Bradley, D. D. C.; Huang, W. 2,3,7,8,12,13-Hexaaryltruxenes: An Ortho-Substituted Multiarm Design and Microwave-Accelerated Synthesis Toward Starburst Macromolecular Materials with Well-Defined π Delocalization. Chem. Eur. J. 2010, 16, 8471-8479. (41) Hurst, J. R.; Schuster, G. B. Nonradiative Relaxation of Singlet Oxygen in Solution. J. Am. Chem. Soc. 1983, 105, 5756-5760. (42) Westenhoff, S.; Daniel, C.; Friend, R. H.; Silva, C.; Sundstrom, V.; Yartsev, A. Exciton Migration in a Polythiophene: Probing the Spatial and Energy Domain by Line-Dipole Forster-Type Energy Transfer. J. Chem. Phys. 2005, 122, 094903-094910. (43) Crawford, A. G.; Dwyer, A. D.; Liu, Z.; Steffen, A.; Beeby, A.; Palsson, L.-O.; Tozer, D. J.; Marder, T. B. Experimental and Theoretical Studies of the Photophysical Properties of 2-and 2,7-Functionalized Pyrene Derivatives. J. Am. Chem. Soc. 2011, 133, 13349-13362. (44) Reghu, R. R.; Grazulevicius, J. V.; Simokaitiene, J.; Miasojedovas, A.; Kazlauskas, K.; Jursenas, S.; Data, P.; Karon, K.; Lapkowski, M.; Gaidelis, V.; et al. Glass-Forming Carbazolyl and Phenothiazinyl Tetra Substituted Pyrene Derivatives: Photophysical, Electrochemical, and Photoelectrical Properties. J. Phys. Chem.

C 2012, 116, 15878-15887.

(45) Karpicz, R.; Puzinas, S.; Krotkus, S.; Kazlauskas, K.; Jursenas, S.; Grazulevicius, J. V.; Grigalevicius, S.; Gulbinas, V. Impact of Intramolecular Twisting and Exciton Migration on Emission Efficiency of Multifunctional Fluorene-Benzothiadiazole-Carbazole Compounds. J. 27 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Chem. Phys. 2011, 134, 204508-204516. (46) Shaw, P. E.; Cavaye, H.; Chen, S. S. Y.; James, M.; Gentle, I. R.; Burn, P. L. The Binding and Fluorescence Quenching Efficiency of Nitroaromatic (Explosive) Vapors in Fluorescent Carbazole Dendrimer Thin Films. Phys. Chem. Chem. Phys. 2013, 15, 9845-9853. (47) Pommerehne, J.; Vestweber, H.; Guss, W.; Mahrt, R. F.; Bassler, H.; Porsch, M.; Daub, J. Efficient 2-Layer LEDs On a Polymer Blend Basis. Adv. Mater. 1995, 7, 551-554. (48) Esboui, M.; Jaidane, N. Non-Radiative Deactivation in Phenol-Pyridine Complex: Theoretical Study. Photochem. Photobiol. Sci. 2015, 14, 1127-1137. (49) Iikura, H.; Mori, S.; Sawamura, M.; Nakamura, E. Endohedral Homoconjugation in Cyclopentadiene Embedded in C60. Theoretical and Electrochemical Evidence. J. Org. Chem. 1997, 62, 7912-7913. (50) Smirnova, O.; Mairesse, Y.; Patchkovskii, S.; Dudovich, N.; Villeneuve, D.; Corkum, P.; Ivanov, M. Y. High Harmonic Interferometry of Multi-Electron Dynamics in Molecules. Nature 2009, 460, 972-977. (51) Zhang, Z.; Zhang, Z.; Chen, R.; Jia, J.; Han, C.; Zheng, C.; Xu, H.; Yu, D.; Zhao, Y.; Yan, P.; et al. Modulating the Optoelectronic Properties of Large, Conjugated, High-Energy Gap, Quaternary Phosphine Oxide Hosts: Impact of the Triplet-Excited-State Location. Chem. Eur. J. 2013, 19, 9549-9561. (52) Adam, G.; Pivrikas, A.; Ramil, A. M.; Tadesse, S.; Yohannes, T.; Sariciftci, N. S.; Egbe, D. A. M. Mobility and Photovoltaic Performance Studies on Polymer Blends: Effects of Side Chains Volume Fraction. J. Mater. Chem. 2011, 21, 2594-2600. (53) Mondal, R.; Ko, S.; Verploegen, E.; Becerril, H. A.; Toney, M. F.; Bao, Z. Side Chain Engineering of Fused Aromatic Thienopyrazine Based Low Band-Gap Polymers for Enhanced 28 ACS Paragon Plus Environment

Page 28 of 31

Page 29 of 31

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Charge Carrier Mobility. J. Mater. Chem. 2011, 21, 1537-1543. (54) Shi, Q.; Fan, H.; Liu, Y.; Chen, J.; Ma, L.; Hu, W.; Shuai, Z.; Li, Y.; Zhan, X. Side Chain Engineering of Copolymers Based on Bithiazole and Benzodithiophene for Enhanced Photovoltaic Performance. Macromolecules 2011, 44, 4230-4240. (55) Tu, G.; Massip, S.; Oberhumer, P. M.; He, X.; Friend, R. H.; Greenham, N. C.; Huck, W. T. S. Synthesis and Characterization of Low Bandgap Conjugated Donor-Acceptor Polymers for Polymer: PCBM Solar Cells. J. Mater. Chem. 2010, 20, 9231-9238. (56) Liu, C.; Fu, Q.; Zou, Y.; Yang, C.; Ma, D.; Qin, J. Low Turn-on Voltage, High-Power-Efficiency, Solution-Processed Deep-Blue Organic Light-Emitting Diodes Based on Starburst Oligofluorenes with Diphenylamine End-Capper to Enhance the HOMO Level. Chem. Mater. 2014, 26, 3074-3083. (57) Liu, C.; Li, Y.; Li, Y.; Yang, C.; Wu, H.; Qin, J.; Cao, Y. Efficient Solution-Processed Deep-Blue Organic Light-Emitting Diodes Based on Multibranched Oligofluorenes with a Phosphine Oxide Center. Chem. Mater. 2013, 25, 3320-3327. (58) Lai, W.-Y.; Xia, R.; He, Q.-Y.; Levermore, P. A.; Huang, W.; Bradley, D. D. C. Enhanced Solid-State Luminescence and Low-Threshold Lasing from Starburst Macromolecular Materials. Adv. Mater. 2009, 21, 355-360. (59) Qian, Y.; Wei, Q.; Del Pozo, G.; Mroz, M. M.; Lueer, L.; Casado, S.; Cabanillas-Gonzalez, J.; Zhang, Q.; Xie, L.; Xia, R.; et al. H-Shaped Oligofluorenes for Highly Air-Stable and Low-Threshold Non-Doped Deep Blue Lasing. Adv. Mater. 2014, 26, 2937-2942. (60) Xia, R.; Lai, W.-Y.; Levermore, P. A.; Huang, W.; Bradley, D. D. C. Low-Threshold Distributed-Feedback

Lasers

Based

on

Pyrene-Cored

Starburst

Molecules

with

1,3,6,8-Attached Oligo(9,9-dialkylfluorene) Arms. Adv. Funct. Mater. 2009, 19, 2844-2850. 29 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(61) Yap, B. K.; Xia, R.; Campoy-Quiles, M.; Stavrinou, P. N.; Bradley, D. D. C. Simultaneous Optimization of Charge-Carrier Mobility and Optical Gain in Semiconducting Polymer Films. Nat. Mater. 2008, 7, 376-380. (62) Yu, L.; Liu, J.; Hu, S.; He, R.; Yang, W.; Wu, H.; Peng, J.; Xia, R.; Bradley, D. D. C. Red, Green, and Blue Light-Emitting Polyfluorenes Containing a Dibenzothiophene-S,S-Dioxide Unit and Efficient High-Color-Rendering-Index White-Light-Emitting Diodes Made Therefrom. Adv. Funct. Mater. 2013, 23, 4366-4376. (63) Xia, R.; Heliotis, G.; Campoy-Quiles, M.; Stavrinou, P. N.; Bradley, D. D. C.; Vak, D.; Kim, D. Y. Characterization of a High-Thermal-Stability Spiroanthracenefluorene-Based Blue-LightEmitting Polymer Optical Gain Medium. J. Appl. Phys. 2005, 98, 083101-083106. (64) Xu, W.; Yi, J.; Lai, W.-Y.; Zhao, L.; Zhang, Q.; Hu, W.; Zhang, X.-W.; Jiang, Y.; Liu, L.; Huang, W. Pyrene-Capped Conjugated Amorphous Starbursts: Synthesis, Characterization, and Stable Lasing Properties in Ambient Atmosphere. Adv. Funct. Mater. 2015, 25, 4617-4625.


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Table of Contents Graphic


Pyrenyl-Capped Benzofiurene Derivatives: Synthesis

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