Manipulating Organic Triplet Harvesting in

Regioisomeric Microcrystals

Table of contents

1. Methods

2. Synthesis

3. Photophysical Properties

I. In Solutions

II. In Microcrystals

4. Crystallography

5. Computation Results

6. References

Electronic Supplementary Material (ESI) for Journal of Materials Chemistry C.This journal is © The Royal Society of Chemistry 2017

1. MethodsCharacterization. 1H NMR spectra were recorded on Varian 400 MHz NMR spectrometer. Electrospray ionization mass spectra (ESI-MS) were performed in positive ion mode on Bruker Apex IV Fourier transform ion cyclotron resonance mass spectrometer. Elemental analyses were measured on a VARIO EL from Elementar Analysensysteme GmbH. Wide angle X-ray diffractometry (WAXD) data were collected using a Panalytical XRD instrument with Cu radiation 1.5406 Å at 40 kV and 40 A, at a scan rate of 9o (2θ) per minute. Single crystal X-ray data of L-mBr were recorded on a SuperNova Dual Atlas CCD diffractometer with Mo/Kα (λ = 0.71073 Å) radiation. Single crystal X-ray data of L-pBr and L-oBr were recorded on Rigaku Pilatus 200 K using the same wavelength radiation. UV-Vis absorption spectra were recorded using a Shimadzu UV-2401 PC spectrometer. Luminescent photographs of microcrystals were taken by a Panasonic DMC-G3 camera and an Olympus BX51 microscope under 365 nm UV light irradiation. The excitation, photoluminescence (PL) spectra and time-resolved emission decay data were obtained using a spectrometer (FLSP980) from Edinburgh Instruments. PL spectra at different temperatures (room temperature to 77 K) were monitored by a FLS980 spectrometer equipped with a temperature control accessory (Oxford Instruments liquid nitrogen cryostates with ITC controller). Lifetimes were obtained on a single photon counting spectrometer from Edinburgh FLS980 with micro-second pulse lamp or 340 nm laser pulse as the excitation source. The absolute quantum yields were measured using a Hamamatsu C9920-02 absolute PL quantum yield measurement system. A dewar flask holder was used for low temperature measurements.

HOMO and LUMO measurements. HOMO, LUMO and the energy gap (Eg) between them were estimated by the first oxidation peak in the cyclic voltammogram and the absorption edge in UV-Vis spectrum. Cyclic voltammetry measurements were carried out in 1 mM CHCl3 with 0.1 M Bu4NPF6 as a supporting electrolyte, AgCl/Ag as a reference electrode, and Pt wire as working and counter electrodes, and scan rate was at 100 mV/s.The HOMO levels were calculated from the empirical formula EHOMO = -(1.4±0.1)×(qVCV) - (4.6±0.08) eV, VCV is determined from the difference between the oxidation potentials at which the reference solute and samples are oxidized.1 The LUMO levels were calculated from ELUMO = EHOMO + Eg, where Eg is derived from absorption edge.

Estimation of kinetic parameters of triplet involving processes. All non-radiative internal convertion processes are neglected. The rate constants of prompt fluorescence (kPF) and delayed fluorescence (kDF) can be obtained experimentally using Equation (1) and (2):2

𝑘𝑃𝐹 =Φ𝑃𝐹

𝜏𝑃𝐹 (1)

𝑘𝐷𝐹 =Φ𝐷𝐹

𝜏𝐷𝐹 (2)

where the fluoroscence efficiency of PF (ΦPF) and DF (ΦDF) were determined from the total PL quantum yields (PLQY) and the ratio between their components which was calculated from the transient PL spectra.3 Negelecting the non-radiative process of the triplet state (knr, T) at room temperature and assuming that the rISC yield is close to unity, the rate constant of intersystem crossing (kISC) and reverse intersystem crossing (krISC) can be obtained from Equation (3) and

Equation (4):

𝑘𝐼𝑆𝐶 =Φ𝐷𝐹

Φ𝐷𝐹 + Φ𝑃𝐹𝑘𝑃𝐹 (3)

𝑘𝑟𝐼𝑆𝐶 =𝑘𝐷𝐹𝑘𝑃𝐹

𝑘𝐼𝑆𝐶

Φ𝐷𝐹

Φ𝑃𝐹 (4)

The phosphorescence rate constant was determined from the reciprocal of the phosphorescence lifetime. kISC in L-oBr were calculated by Equation 5 with the assumption that

only fluorescence and ISC processes deactivate the lowest excited singlet states.4 is the intrinsic 𝑘0𝑓

rate constant of fluorescence, kf is the apparent rate constant of fluorescence. The fluorescence efficiency (Φf) was determined from the total PL quantum yields (PLQY) and the ratio of fluorescence peak integrated area.

𝑘𝐼𝑆𝐶 = 𝑘𝑓 ‒ 𝑘0𝑓 =

1𝜏𝑓

‒Φ𝑓

𝜏𝑓 (5)

Preparation of co-ground mixture of L-mBr with a europium complex. The co-ground mixture was prepared in an agate mortar with ethanol as a grinding assistant. Grinding for several minutes, ethanol evapourated and a white solid was obtained.

DFT calculations. The Gaussian 09 program was utilized to perform the DFT/TD-DFT calculations. Considered the importance of intermolecular interactions in dimers, long-range corrected functional wB97XD5 was employed in DFT and TD-DFT calculations. To simulate the fluorescence and phosphorescence spectra of microcrystal samples, the excited state geometries of different types of dimers, which were obtained from the single crystal structures, need furture optimization in order to calculate the lowest excited states of a given multiplicity. Natural transition orbitals (NTOs) of excited states, a means of finding a compact orbital representation for the electronic transition density matrix, were calculated by Gaussian 09 program.6

2. SynthesisL-(p,m,o)Br were facilely prepared through nucleophilic addition reaction between benzoyl

chloride and carbazole. The identity of L-(p,m,o)Br was confirmed by 1H-NMR, 13C-NMR and ESI-MS.

O

ClR1R2

R3

HN (1) NaH, THF, 60 oC

(2)

NO

R1

R2

R3

L-pBr: R1=R2=H, R3=Br

L-mBr: R1=R3=H, R2=Br

L-oBr: R2=R3=H, R1=Br

Figure S1. Synthetic route to L-pBr, L-mBr, and L-oBr.N-(4-bromobenzoyl)-carbazole (L-pBr). Into a 50 mL three-necked round-bottom flask was placed carbazole (1.67 g, 10 mmol). The flask was evacuated under vacuum and flushed with

nitrogen for three times. Then dry THF (20 mL) was injected. Sodium hydride (0.80 g, 20 mmol) was added to the flask under nitrogen flux. The reaction mixture was heated to 60 oC and stirred for 30 min, and then cooled down to 0 oC. To this reaction mixture was added 4-bromobenzoyl chloride (3.29 g, 15mmol) drop-wise, with stirring. The mixture was further heated at 60 oC and stirred overnight. The resulting suspension was diluted with water carefully. The crude product was filtrated and then purified by flash chromatography (silica gel, PE/DCM, 9/1, v/v), affording a white needle-like crystal was obtained (2.45 g, 70%). 1H NMR (400 M, DMSO-d6, δ): 8.26-8.18 (m, 2H), 7.83 (d, J = 8.4 Hz, 2H), 7.69 (d, J = 8.5 Hz, 2H), 7.42 (qd, J = 6.2, 4.0 Hz, 6H). 13C NMR (400 M, CDCl3, δ): 168.51, 138.99, 134.48, 132.26, 130.77, 127.31, 126.87, 126.10, 123.64, 119.96, 115.71. ESI-MS (m/z): calcd for C19H12BrNO 349.01, found 350.0 (M+H+). Found: C, 65.16; H, 3.55; N, 4.01. Calc. for C19H12BrNO: C, 65.16; H, 3.45; N, 4.00%.N-(3-bromobenzoyl)-carbazole (L-mBr). The synthetic procedure for L-mBr is similar to that of L-pBr. A white solid was obtained (1.75 g, 50%). 1H NMR (400 M, CDCl3, δ): 8.05 – 7.99 (m, 2H), 7.89 (s, 1H), 7.78 (dt, J = 8.1, 1.4 Hz, 1H), 7.62 (dd, J = 7.8, 1.4 Hz, 1H), 7.55 – 7.48 (m, 2H), 7.45 – 7.30 (m, 5H). 13C NMR (400 M, CDCl3, δ): 167.87, 138.92, 137.63, 135.32, 131.90, 130.45, 127.56, 126.93, 126.19, 123.76, 123.03, 119.96, 115.78. ESI-MS (m/z): calcd for C19H12BrNO 349.01, found 350.0 (M+H+). Found: C, 65.29; H, 3.50; N, 3.95. Calc. for C19H12BrNO: C, 65.16; H, 3.45; N 4.00%.N-(2-bromobenzoyl)-carbazole (L-oBr). The synthetic procedure for L-oBr is similar to that of L-pBr. A white solid was obtained (1.54 g, 88%). 1H NMR (400 M, CDCl3, δ): 7.99 (d, J = 8.4 Hz, 2H), 7.72(d, J = 7.8 Hz, 1H), 7.61-7.28 (m, 9H). 13C NMR (400 M, CDCl3, δ): 167.25, 138.54, 138.48, 133.64, 131.98, 128.86, 128.27, 127.34, 126.69, 124.20, 119.85, 119.82, 115.92. ESI-MS (m/z): calcd for C19H12BrNO 349.01, found 350.0 (M+H+). Found: C, 65.16; H, 3.59; N, 4.00. Calc. for C19H12BrNO: C, 65.16; H, 3.45; N 4.00%.

Further purification of L-(p,m,o)Br has been made by use of a physical vapor-transport method in a horizontal tube furnace at around 10 Pa pressure. Single crystals of L-(p,m,o)Br were grown from dichloromethane/ethanol mixtures. All the sublimated samples were confirmed as crystalline forms through the intense diffraction peaks in the wide-angle X-ray diffraction (WAXD). The XRD patterns of sublimated L-(p,m,o)Br are nearly the same as the simulated diffraction patterns from the single crystals grown by the solution method, which indicates that no new polymorph was produced during the heating process (Fig. S2). Fast aggregation samples were prepared by dipping the tetrahydrofuran solutions to water quickly, and then collected by centrifugation. After 24 hours vacuum drying at 65 oC, fast aggregation samples were ready for various measurements.

Figure S2. XRD patterns of L-pBr (left), L-mBr (middle) and L-oBr (right): (A) Calculated from

single crystal grown by the solution method, (B) As-prepared samples.

3. Photophysical propertiesI. In Solutions

Figure S3. UV-Vis absorption spectra of L-(p,m,o)Br in CH2Cl2 (1 × 10-5 M).

Figure S4. Molecular frontier orbitals diagram for HOMOs and LUMOs of L-pBr, L-mBr and L-oBr (solid line: experiment measurement results, dash line: calculation results).

Figure S5. Cyclic voltammograms of (a) L-(p,m,o)Br and (b) ferrocene in CHCl3.

Figure S6. PL spectra of (a) L-pBr and (b) L-mBr in solvents (5 × 10-5 M) having different polarities. The peaks that change significantly with different solvent polarities were normalized to same intensity.

Figure S7. Normalized phosphorescence spectra (delay 3 ms) of L-(p,m,o)Br in 2-MTHF (1 × 10-5 M) at 77 K.

Table S1. The photophysical properties of L-(p,m,o)Br in solutionsλEm,77

a

[nm]λEm,RT

b

[nm]τRT

(%)Φsol

d

[%]

L-pBr 414,444,467 5553.12 ns (12)145 ns (88)

5.0

L-mBr 414,444,467 5653.06 ns (34)101 ns (66)

2.9

L-oBr 416,446,469 367,385,404 6.0c ns 6.2a. Measured in 2-methyltetrahydrofuran (2-MTHF, 1 × 10-5 M) at 77 K. b. Measured in CHCl3 (1 × 10-5 M) in air at room temperature. c. Mean lifetime. d. Φ = quantum yield, solution efficiencies (Φsol) were determined with the excitation wavelength of 330 nm.

II. In MicrocrystalsThe lifetime decay profiles of L-(p,m,o)Br are shown in Fig. S9a-S9c. Due to the overlapped

emission peaks in L-mBr, lifetimes were distinguished by gated spectra with different delay times (Fig. S8). The effects of low temperature on the PL of L-(p,m,o)Br micro-crystals were investigated. We note that not only the spectra (Fig. S9d-S9e) but also the kinetics of phosphorescence for the three crystals are strongly temperature dependent (Table S2). When the temperature decreases from room temperature to 77 K, the phosphorescent emission intensities of L-mBr and L-oBr increase, while the para- substituent isomer changes in an opposite way (Fig. S9d). It is confirmed that L-pBr is a TADF material in which up-conversion from triplet to singlet states is accelerated by heat. The evolution of temperature-dependent spectral shape in L-(p,m,o)Br series shows three different characteristics: a 14 nm red-shift and fine-structured emission is observed at 77 K for L-pBr (Fig. S9d), finer vibrational structure is presented for L-mBr (Fig. S9e), and higher triplet levels arises in L-oBr (Fig. S9f).

360 400 440 480 520 560 600 640 680 720

Nor

mal

ized

Inte

nsity

(a.u

.)

Wavelength (nm)

Em Delay 0.05 ms Delay 1 ms

Figure S8. The steady (black) and gated (red and blue) spectra of L-mBr microcrystals at room temperature.

Table S2. The photophysical properties of L-(p,m,o)Br in microcrystals

λEm,77

[nm]τ77 K

[ms]Φ77 K[%]

Φfast

[%]L-pBr 489; 524 371; 419 11 8

L-mBr

471; 482; 502533578631

20.1; 22.3; 22.216.7 (71%) 256 (29%)16.7 (59%) 295 (41%)16.9 (53%) 311 (47%)

49 5

L-oBr460495537

141 (31%) 462 (69%)133 (20%) 482 (80%)133 (24%) 461 (76%)

32 9

Figure S9. a, Lifetime decay profiles of emission band at 473 nm of L-pBr excited by 340 nm. The inset is the decay profile of prompt component at 473 nm. b, Lifetime decay profiles of emission bands (472, 529 nm) of L-mBr excited by 340 nm. The inset is the decay profile of 472 nm. c, Lifetime decay profiles of emission bands (530, 575 nm) of L-oBr excited by 340 nm. d, e, f, The steady-state PL spectra of L-pBr, L-mBr, and L-oBr recorded with decreasing temperature from room temperature to 77 K, respectively.

4. CrystallographyThe crystal structures were solved by the direct method using SHELXS program and refined

by least squares method on F2, SHELXL, which were incorporated in OLEX2.7 Hydrogens were calculated by geometrical methods and refined as a constrained coordinates.

Figure S10. Single-crystal structures of (a) L-pBr, (b) L-mBr and (c) L-oBr. Thermal ellipsoids are drawn at 50% probability level. The configurations of three molecules share a common feature that C=O is inclined to be coplanar with carbazole moieties, which is driven by intramolecular C-H· · ·O=C contact.

Table S3. Crystal data of L-(p,m,o)Br crystals

L-oBr L-mBr L-pBr

CCDC 1540850 1534317 1533213

Empirical formula C19H12NOBr C19H12NOBr C19H12NOBr

Crystal colour colourless colourless colourless

Formula weight 350.21 350.21 350.21

Temperature/K 113 180 113

Crystal system monoclinic monoclinic monoclinic

Space group P21/n I2/a P21/n

a/Å 8.2389(16) 21.5976(18) 11.5066(15)

b/Å 9.5522(18) 7.7186(4) 10.2017(13)

c/Å 18.470(3) 18.3872(16) 12.3497(16)

α/o 90.00 90 90

β/o 91.861(5) 110.435(10) 95.332(4)

γ/o 90.00 90 90

Volume/Å3 1452.8(5) 2872.3(4) 1443.4(3)

Z 4 8 4

ρcalc mg/mm3 1.601 1.620 1.612

F(000) 704 1408 704

μ/mm 2.830 2.863 2.848

RadiationMo Kα

(λ= 0.71073)Mo Kα

(λ= 0.71073)Mo Kα

(λ= 0.71073)

θ range /o 3.06 - 27.50 2.89 - 27.48 3.06 - 27.54

Independent reflections 3284 2821 3305

Rint 0.0667 0.0469 0.0345

R1/wR2 [I>2σ(I)] 0.0300/0.0734 0.0495/0.1197 0.0205/0.0565

R1/wR2 [all data] 0.0384/0.0742 0.0741/0.1344 0.0230/0.0570

Goodness-of-fit on F2 0.933 1.056 1.101

Residual peak / hole e.Å-3 0.785 / -0.562 1.758 / -0.654 0.276 / -0.470

Figure S11. (a) C-H· · ·Br interaction in L-pBr. (b) C-Br· · ·Br-C interaction in L-oBr, θ1=θ2=141.6 °.

L-oBr

L-mBr

L-pBr2.93 Å

3.39 Å

3.18 Å

6.58 Å

Figure S12. Two different dimer conformations of L-(p,m,o)Br. Left column: head-to-tail dimer; right column: slipped-parallel dimer. The dimer in grey background refers to the intermolecular interactions between two molecules are weak.

5. Computation ResultsThe long-range corrected functional wB97XD2 employing the 6-31G+* basis sets (lanl2dz for

Br atoms) was used for the calculations. From geometrical optimizations with the single crystal structures as starting geometries, we determined frontier orbitals and binding energies of head-to-tail and slipped-parallel dimers of L-(p,m,o)Br in the ground state (except slipped-parallel dimer of L-oBr, similarly hereinafter). The ground state geometries (S0) of dimers maintain the specific molecular configurations and intermolecular locations corresponding to the single crystal structures (Supplementary Fig. 16).

TD-DFT calculations were employed to model the vertical excitation of each N-benzoyl-carbazole dimer at its optimized ground state geometry (S0,opt). Fluorescence and phosphorescence emissions of L-(p,m,o)Br were simulated by the TD-DFT method based on optimized molecular structures at the singlet or triplet excited state to obtained the lowest n-th singlet and n-th triplet states, as the equilibrium positions of atoms for the excited states, usually, are different from those

of the ground state.8

Supplementary Table 4. Binding energies (BEs) and excited states (S1, T2, and T1) energy levels of L-(p,m,o)Br.

BE[eV]

S1,vertical

[eV]f

S1,opt

[eV]f

T1

[eV]T2

[eV]

sPa 0.58 4.58b 0.32b 2.54 0.0006 2.13 2.46L-pBr

H2Ta 0.54 4.61b 0.16b 2.57 0.0021 2.11 2.48

sP 0.68 4.36 0.44 2.54 0.0002 2.34 3.25L-mBr

H2T 0.62 4.32 0.28 2.42 0.0002 2.38 3.29

L-oBr sP 0.59 4.79 0.38 2.44 0.0005 2.32 3.24

a. sP stands for the slipped-parallel dimer; H2T stands for the head-to-tail dimer.b. The vertical excitation energy and oscillator strength (f) of L-pBr are S2 state.

The possible S1 to T1 (or T2) ISC channels are believed to share part of the same transition orbital compositions, and the energy gap between S1 and the specific Tn should be small (usually smaller than 0.3 eV).9, 10 Orbital configurations and the most possible ISC channels of different dimers of L-(p,m,o)Br are represented in Table S5-S7.

Table S5. The singlet and triplet states transition configurations of slipped-parallel (sP) dimer and head-to-tail (H2T) dimer of L-pBr. The matched excited states with same orbital transition components and a suitable energy gap were highlighted in red.

n-thEnergy

(eV)Transition configuration (%)

S1 2.54 H-11→L (4.99), H→L (86.47), H→L+11 (3.15)

T2 2.43H-17→L (3.67), H-16→L (11.66), H-11→L (3.03),H-8→L (15.57), H-7→L (34.35), H-6→L (11.27),H-4→L+11 (9.58), H-7←L (2.08)

sP dimer

T1 2.11H-16→L (3.36) H-11→L (3.39), H-8→L (18.73),H→L (51.42), H→L+1 (2.90)

S1 2.57H-12→L (3.60), H-11→L (2.95), H→L (84.85),H→L+11 (2.91)

T2 2.46H-17→L (7.40), H-16→L (6.83), H-9→L (10.73),H-7→L (3.35), H-6→L (18.94), H-5→L (5.34),H-4→L (8.97)

H2T dimer

T1 2.13H-16→L (2.18), H-9→L (12.64), H-8→L (12.38),H-7→L (3.82), H-6→L (6.30), H→L (49.05),H→L+11 (2.51)

Table S6. The singlet and triplet states transition configurations of slipped-parallel (sP) dimer and head-to-tail (H2T) dimer of L-mBr. The matched excited states with same orbital transition components and a suitable energy gap were highlighted in red.

n-thEnergy

(eV)Transition configuration (%)

S1 2.54 H-11→L (5.48), H→L (84.74), H→L+11 (2.84)

T2 3.29H-11→L+11 (5.30), H-6→L+3 (2.08), H-2→L+1 (5.59), H-2→L+3 (2.08), H-2→L+4 (2.75), H-1→L+8 (12.73)sP dimer

T1 2.39H-12→L (4.64), H-3→L+10 (2.22), H→L (36.45),H→L+1 (6.40), H→L+2 (47.44), H←L+2 (2.52)

S1 2.42 H-14→L (3.90), H→L (88.89), H→L+11 (2.65)

T2 3.25H-12→L+13 (2.48), H-6→L+3 (2.22), H-2→L+1 (6.88), H-2→L+2 (2.55), H-2→L+3 (49.33), H-2→L+5 (2.79), H-1→L+8 (13.16)

H2T dimer

T1 2.35H-11→L+13 (2.05), H→L (14.71), H→L+1 (27.33), H→L+2 (48.29), H←L+2 (2.70)

Table S7. The singlet and triplet states transition configurations of slipped-parallel (sP) dimer of L-oBr. The matched excited states with same orbital transition components and a suitable energy gap were highlighted in red.

n-thEnergy

(eV)Transition configuration (%)

S1 2.44H-12→L (4.79), H-11→L (2.14), H-9→L (3.96), H→L (82.48), H→L+11 (2.77)

T2 3.24H-11→L+13 (4.57), H-7→L+3 (3.97), H-2→L+1 (3.20),H-2→L+10 (10.88), H-1 →L+1 (27.74), H-1→L+3 (33.87)

sP dimer

T1 2.32H-12→L+12 (3.82), H-3→L+11 (3.57), H→L (77.49), H→L+2 (13.61), H←L (3.59)

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