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From Dipyrrolonaphthyridinediones to Quinazolinoindolizinoindolizinoquinazolines Bart#omiej Sadowski, David J. Stewart, Alexis T. Phillips, Tod A. Grusenmeyer, Joy E. Haley, Thomas M. Cooper, and Daniel Tomasz Gryko J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.9b00839 • Publication Date (Web): 27 May 2019 Downloaded from http://pubs.acs.org on May 27, 2019

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The Journal of Organic Chemistry

From Dipyrrolonaphthyridinediones to Quinazolinoindolizinoindolizinoquinazolines Bartłomiej Sadowski,a David J. Stewart,b,c Alexis T. Phillips,b,d Tod A. Grusenmeyer,b Joy E. Haley,b Thomas M. Cooperb* and Daniel T. Grykoa* a

Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland Air Force Research Laboratory, Materials and Manufacturing Directorate, Functional Materials Division, Wright-Patterson AFB, Ohio 45433-7750, United States b

c

General Dynamics Information Technology, 5100 Springfield Pike, Dayton, Ohio 45431, United States

d

Southwestern Ohio Council for Higher Education, Dayton, Ohio 45420, United States

Supporting Information Placeholder

ABSTRACT: The dipyrrolonaphthyridinedione (DPND) core can be readily converted into π-expanded, acid-responsive quinazolinoindolizinoindolizinoquinazoline (QIIQ) through a two-step route involving direct arylation followed by acid-catalysed condensation. Unlike the majority of previously obtained DPNDs, these non-planar dyes bearing 8 fused rings, are almost non-fluorescent, which is attributed to fast internal conversion (IC) relative to radiative decay and intersystem crossing (ISC).

Polycyclic aromatic hydrocarbons (PAHs)1 and their heterocyclic analogues possessing π-expanded structures2 have experienced a renaissance due to their high charge-carrier mobility and hence their potential applications in the field of organic electronics, such as organic light-emitting diodes (OLEDs),3 organic field effect transistors (OFETs)4 as well as dye-sensitized solar cells.5 Their large π-surfaces enable regular crystalline-state packing and electron transduction. Planar ladder-type PAHs are well-known class of these materials and have been thoroughly studied from an optoelectronic perspective. 2 The recently discovered dipyrrolonaphthyridinedione (DPND) core serves as an excellent scaffold in the design of strongly fluorescent dyes,6 efficient two-photon materials7 or molecules with emission in the red/NIR region of the spectrum.8 Our recent studies on the reactivity of this core have proven that it can be readily functionalized at the pyrrole moiety by employing a bromination/coupling reaction sequence6-8 or direct arylation reaction.6b,9 We were motivated to explore this subject in more detail since the reactivity of the carbonyl moiety within the DPND core has not been investigated before, and therefore may open an exciting avenue for further research.

Inspired by works from Shinokubo’s group 10 on the acid-catalysed condensation towards pyridine-fused perylene bisimides we envisioned that such a transformation performed on the DPND core should lead to structurally unique analogs of nitrogen-doped PAHs (Figure 1), which partially resemble a part of the fullerene C60 carbon skeleton. We expected that such a condensation may be challenging due to decreased electrophilic character of the carbonyl bond caused by the presence of a pyrrole ring within the DPND core. Herein we present results of our studies.

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Table 1. Synthesis of arylated DPNDs and the products of their intramolecular condensation. Aryl bromide

Figure 1. General structure of the QIIQ skeleton.

We began our investigation with the preparation of the corresponding bis(aryl)DPNDs 2a-d using direct arylation9,11 between the DPND and 2-bromoacetanilides 1a-d (Scheme 1). Next, we carried out several condensation processes using concentrated HCl (for 2a, 2c, and 2d) or a mixture of HClconc/H2SO4 conc (for 2b and 2d) and finally we obtained three examples of π-expanded quinazolinoindolizinoindolizinoquinazoline (QIIQ) 3a-c. We also found that organic acids (TFA or methanesulphonic acid) are not able to mediate such condensation. In the case of compound 2d, nucleophilic character of the amine groups (obtained in situ through hydrolysis of an acetanilide moiety) is significantly decreased due to strong negative inductive and negative resonance effects of NO2 group placed at para positions, thus the condensation process was ineffective employing both types of conditions. In the case of 2b bearing CF3 group, we obtained the corresponding product 2b in 60% yield as in this case only negative inductive effect applies.

R

2 (yield)

3 (yield)

1a

H

2a (29%)

3a (78%)

1b

CF3

2b (53%)

3b (60%)

1c

OMe

2c (34%)

3c (37%)

1d

NO2

2d (30%)

3d (traces)

In the literature, there is no evidence for the quinazolinoindolizinoindolizinoquinazoline (QIIQ) skeleton (Figure 1). Derivatives of 6-azaindolizine have been known since the late 1940s,12 however optical behaviour of unsubstituted 6-azaindolizine has been barely investigated.12a,13 The unsubstituted pyrrolo[1,2-c]quinazoline molecule is unknown although its derivatives have been widely investigated in terms of their biological activity.14 Absorption and normalized emission spectra in toluene are shown in Figure 2 and summarized in Table 2. The absorption spectra are characterized by strong transitions (~4 × 104 M−1 cm−1) around 310 nm with slightly weaker transitions just less than 3 × 104 M−1 cm−1 at the visible absorption maxima (~600 nm). Hence, the spectra shift bathochromically relative to the parent DPNDs6a to energies similar to that observed previously for the π-expanded DPND dyes.7 The absorption spectra of all three dyes are quite similar, although those of 3a and 3c have a more structured spectra at the visible maxima whereas 3b is broader. The emission spectra are structured and tail to ~1100 nm due to vibronic transitions. The absorption and emission spectra are not mirror images. This is evidence for the equilibrium S1 state having a different conformation than the ground state, supported by calculation results described below. Dyes 3a and 3c are essentially isoenergetic (679 nm vs 678 nm at their emission peak maxima, respectively) while 3b is slightly lower in energy (704 nm at peak maximum). Excitation spectra (Figure S1, ESI) overlay quite well with the absorption spectra, indicating the observed emission is from the absorbing species. In stark contrast to the DPND dyes,6-9 these dyes are extremely poor emitters, with Φfl ranging from 1.8 × 10−4 (3b) – 2.3 × 10−3 (3c). Across the series, 3c with the electron-donating methoxy substituents has the largest Φfl, followed by the parent dye 3a, then 3b with the electron-withdrawing trifluoromethyl substituents.

Scheme 1. General method for the synthesis of dyes 3a-d. Conditions: a) Pd2dba3, PCy3·HBF4, PivOH, K2CO3, 120°C, 3-5 days; b) HClconc or HClconc/H2SO4 conc, MeOH, 80°C, 30h.


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The Journal of Organic Chemistry to knr.6-9 We attempted to obtain the triplet energies from 77K phosphorescence measurements, but did not observe any phosphorescence out to 1700 nm. Table 3. Results of computational studies of dyes belonging to the QIIQ series. Cmpd.

3a

3b

3c

E(S1)

2.25 (H→L)

2.23 (H→L)

2.23 (H→L)

f (S0→S1)

0.97

1.01

1.05

E(S2)b

2.54 (H→L+1)

2.43 (H→L+1)

2.62 (H→L+1)

f (S0→S2)

0.0004

0.0004

0.0007

1.88

1.77

1.85

0.91

0.60

0.98

0.78

0.79

0.76

re-

E(S1 laxed)a Figure 2. Absorption (solid) and emission (dotted) spectra of 3a (black), 3b (red) and 3c (blue) in toluene. Emission spectra from 570 nm excitation.

Table 2. Spectroscopic properties of dyes belonging to QIIQ series in toluene.

a

Cmpd.

3a

3b

3c

λabs/nm

306/596

311/608

312/597

10-4·ε/ M-1·cm-1

4.3/2.9

3.5/2.6

4.5/2.7

λem/nm

679

704

678

τ/ps

32

17

81

10-3·fla

0.83

0.18

2.3

τrb/ns

39

94

35

The fluorescence quantum yield (Φfl) of 3c in toluene was obtained using Nile Blue (Φfl = 0.271 in ethanol) as a standard and corrected for refractive index differences of the solvents. 3c was chosen as it is the most emissive, and Φfl of 3a and 3b were then referenced to 3c. b S1 state radiative lifetime calculated from Φfl and S1 state lifetime. Because the fluorescence lifetimes are too short to be measured using time-correlated single-photon counting, ultrafast transient absorption measurements were used to obtain them. The lifetimes are all < 100 ps, and trend with the fluorescence quantum yields (3c > 3a > 3b). The transient absorption difference spectra are shown in Figure S2 (ESI) at various time delays. Although the transient signals are low, the spectra show positive features at short wavelengths and in the NIR, with bleaches observed at the ground-state absorption maxima. It should be noted that the relatively strong, positive signal in the NIR for 3c is not observed. One explanation is that because the transient absorption signal is weak, stimulated emission mitigates the positive signal. This is only observed for 3c because it is the best emitter. Transient absorption was also tried on the nanosecond time-scale in deaerated toluene, but signals were either extremely weak or not observable, indicating intersystem crossing is either nonexistent or slow. Coupled with the low Φfl values, the results indicate that nonradiative decay (knr > 1010 s−1 for all three dyes) is much greater than both radiative decay (kr) and intersystem crossing (kisc), and indicates internal conversion is the dominant decay pathway. This is notable when comparing these dyes to the DPND dyes where kr is of similar magnitude

fem )c

E(T1

Energies are given in eV. a S1 state energy from equilibrium geometry. b Energies of S2 state calculated for the relaxed S1 geometry. c T1 state energy from equilibrium geometry. H – HOMO; L – LUMO. In an attempt to gain insight into the photophysics of dyes 3a-c, we performed additional quantum chemistry calculations for all QIIQs (Table 3 and Figure 3). All DFT geometry minimizations (ground state, S1 state and T1 state) included frequency calculations that gave no imaginary frequencies. Table 3 presents TDDFT results. The S1 state energies and oscillator strengths were constant for the three chromophores, in agreement with measured λmax and extinction coefficient. The S1 state is a HOMO→LUMO transition for all three chromophores. Both HOMO and LUMO are evenly distributed over the whole molecule. The shapes for 3b and 3c are nearly identical to 3a (Figure 3a and Table S5 in ESI). The equilibrium S1 state energy estimates the emission energy, where E(CF3) < E(H) ~ E(OCH3). Finally E(T1) is predicted to be around 0.8 eV for all three chromophores. One possible explanation for the efficient energy dissipation through internal conversion is the energy gap law, which specifies an enhanced quenching of fluorescence via vibrational overlaps between S1 (v’ = 0) and S0 (v = n) upon lowering the S1-S0 energy gap.15 The obtained molecules are propeller-shaped, multiatomic systems with many vibrational modes capable of acting as acceptors for the dissipation of energy. Moreover, for 3a-c, the almost completely dark S2 state, which is a HOMO→LUMO+1 transition, lies only about 0.3 0.4 eV above the S1 state. Such small energy gap between these states also may result in efficient internal conversion through mixing of vibrational modes as explained earlier. Indeed, the S2-S1 energy gap correlates with the S1 lifetime; the smaller the gap, the shorter the lifetime. All the dyes had calculated nonplanar geometry. The molecule has a propeller shape with the dihedral angle θ = 14-15 degrees in the ground state, while angle decreases in the both S1 and T1 excited states to ~6-8 degrees (Figure 3b).



Figure 3. a. HOMO (left) and LUMO (right) shapes calculated for dye 3a. b. Structures of compound 3a in S0, S1 and T1 states determined by DFT methods (side view). θ - dihedral angle measured using four atoms denoted as black circles.

As the designed molecules contain basic nitrogen atoms, we investigated the potential of 3a to serve as an acid-responsive material by protonation experiments (Figure 4). To our surprise, the addition of up to 2.0 equivalents of trifluoroacetic acid (TFA) to a dichloromethane solution of 3a led to no pronounced changes in the UV-VIS spectrum. This is probably due to significant steric congestion caused by the presence of longer alkyl chains. On the addition of an excess of trifluoroacetic acid (up to 92 eq of TFA – green curve in Figure 4a) the main absorption band located around 600 nm weakened and two new absorption bands appeared: the shorter-wavelength band centered at 467 nm and the longer-wavelength located at 779 nm. The spectra shows isosbestic point at 662 nm, indicating there are only two species in the solution – 3a and mono-protonated individual. The second band, located in the NIR region of the spectrum, can be then attributed to mono-protonated species where positively charged nitrogen are electronically connected with pyrrole-type nitrogen atoms. The addition of higher amounts of TFA (up to 416 eq – blue curve in Figure 4a) caused much smaller spectral changes. Titration of the solution of 3a in dichloromethane with much stronger acid – methanesulfonic acid (MsOH) should shift the equilibrium toward double-protonated species. Upon addition of MsOH (0-10 eq, Figure 4b) spectrochemical behavior was found to be similar as previously noted for the titration with TFA, that is mainly mono-protonation took place (logK1 = 4.3). With higher amounts of MsOH (10-250 eq, Figure 4c), double-protonated compound is formed (logK2 = 2.3) and hence we observed a new, hypsochromically shifted band centered at 675 nm, while the broad band located above 700 nm disappeared completely. Finally, the conversions from neutral form to either mono- or double-protonated species are all reversible, as we were able to obtain identical absorption spectra (and hence the color) after adding an excess of Et 3N to both acidic solutions of 3a (Figure 4d). We also found that the weak fluorescence response noted for 3a vanishes completely upon protonation in both cases.

Figure 4. Changes in the absorption spectra and color of 3a in

CH2Cl2 (2.8∙10-5 M): a. upon addition of TFA (0-416 eq); b. upon addition of MsOH (0-10 eq); c. upon addition of MsOH (10-250 eq); d. photo of cuvettes containing 3a in CH2Cl2 solution before and after adding a large excess of TFA (left) and MsOH (right). According to cyclic voltammetry (CV) measurements (Tables S6 and S7 in ESI), compound 3a undergoes one reversible reduction and two reversible oxidation processes in the accessible potential range in dichloromethane. In contrast to the majority of DPND dyes,6,8-9 the ELUMO values determined for derivatives 3a and 3c lie higher than -3.0 eV, which means that a carbonyl group generally provides stronger stabilization of the LUMO level compared to an imine moiety. The introduction of trifluoromethyl groups (3b) results in the LUMO level lying below -3.0 eV. At the same time, the values of EHOMO calculated for dyes 3a-c are similar to values noted before for electron-rich DPNDs8 containing amine groups directly attached to the core. In conclusion, a convenient synthetic pathway leading to an unprecedented class of N-doped polycyclic aromatic hydrocarbons has been developed. This work demonstrates that the dipyrrolonaphthyridinedione core can also be effectively modified not only in a pyrrole region, but also within carbonyl moieties leading to acid-responsive molecules. Such dyes are an intense blue in solution and, in contrast to other DPND-based dyes, are almost non-fluorescent due to efficient energy dissipation through internal conversion (IC). According to DFT calculations, molecules belonging to the QIIQ series have propeller-like structure, probably due to strain similar to that of corannulene and fullerene. This work open up a new chapter in the chemistry of not only dipyrrolonaphthyridinediones but also aza-analogues of PAHs.

EXPERIMENTAL SECTION General Remarks


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The Journal of Organic Chemistry All reagents and solvents were purchased from commercial sources and were used as received unless otherwise noted. Reagent grade solvents (CH2Cl2, hexanes) were distilled prior to use. Toluene was dried by distillation over sodium and stored under argon. Transformations with moisture- and oxygen-sensitive compounds were performed under a stream of argon. The reaction progress was monitored by means of thin-layer chromatography (TLC), which was performed on aluminum foil plates, covered with silica gel 60 F254 or aluminum oxide 60 F254 (neutral). Chromatography was performed on silica gel (Kieselgel 60, 200-400 mesh). The identity and purity of prepared compounds were proved by 1H NMR and 13C NMR spectrometry as well as by mass spectrometry (via EI-MS or ESIMS). HRMS (ESI-TOF) and HRMS (EI): double-focusing magnetic sector instruments with EBE geometry were utilized. NMR spectra were measured on 500 or 600 MHz instruments with TMS as internal standard. All melting points for crystalline products were measured with an automated melting point apparatus and are given without correction. All chemicals were used as received, unless otherwise noted. DPND6a and 1a-d10a,16 were synthesized as described earlier. Optical Measurements Ground-state UV/vis absorption spectra were measured on a Cary 5000 spectrophotometer. Luminescence spectra were obtained using an Edinburgh Instruments FLS980 spectrometer. Due to the very weak emission, the spectra were collected in 1 mm cuvettes at a 45 degree angle to suppress solvent scattering peaks. The emission spectra were obtained using both a Hamamatsu R928P PMT (spectral range 200 nm – 870 nm) in a cooled housing (−20°C) and a Hamamatsu R5509-72 PMT (spectral range 300 – 1700 nm) in a nitrogen-flow cooled housing (operating temperature −80°C), with the spectra intensity matched and joined at 825 nm. The fluorescence quantum yield (Φfl) of 3c in toluene was obtained using Nile Blue (Φfl = 0.27 in ethanol17) as a standard and corrected for refractive index differences of the solvents. 3c was chosen as it is the most emissive, and Φfl of 3a and 3b were then referenced to 3c. To ensure reliability in the quantum yield measurements, 1 cm cuvettes were required. To remove solvent scattering peaks, the spectra obtained in 1 mm cuvettes were then used after intensity matching to the 1 cm spectra in a region without scattering. All experiments were performed at room temperature. Ultrafast transient absorption measurements were performed using a modified version of the femtosecond pump-probe UVVIS spectrometer described elsewhere.18 Briefly, 4 mJ, 45 fs pulses at 785 nm at 1 kHz repetition rate were obtained from a cryogenically-cooled, Ti:Sapphire regenerative amplifier (KM Labs Wyvern 1000-10). Approximately 5% (0.2 mJ) was reflected into the experiment, which was split into pump and probe (90 and 10%, respectively) by a beam splitter. The pump beam was directed into a frequency doubler (CSK Super Tripler) and then was focused into the sample. The probe beam was delayed in a computer-controlled optical delay (Newport MM4000 250 mm linear positioning stage) and then focused into a sapphire plate to generate white light continuum. The white light was then overlapped with the pump beam in a 2 mm quartz cuvette and then coupled into a CCD detector (Ocean Optics S2000 UV-VIS). Data acquisition was controlled by software developed by Ultrafast Systems LLC. Due to limitations in the experiment, the samples must be excited at 400 nm, a relative minimum of the dyes. Additionally, in order to maintain transparency throughout the visible, the absorbance at the

peak maxima had to be kept below 1.0. This gives absorbance values at 400 nm of around 0.1, and leads to very weak transient absorption signals. However, sufficient averaging still provided good signal-to-noise and allowed for reliable lifetimes to be obtained. Average lifetimes were determined from fits of at least five individual wavelengths near the transient absorption maxima. Computational Studies DFT calculations were performed using Gaussian 16W revision B.01. All geometry minimizations (ground state, S1 state and T1 state) included frequency calculations that gave no imaginary frequencies. The basis set was 6-311g(2d,p) for C, H and F. We added diffuse functions for N and O(6-311+g(2d,p)). All calculations simulated a toluene solvent by PCM. The functional was B3LYP for ground and T1 state calculations and CAM-B3LYP for TDDFT and S1 state optimizations. The T1 state energy was calculated as E(T1) – E(S0, T1 geometry). Experimental Procedures General procedure for the synthesis of dyes 2a-2d. According to the literature procedure,9 in a 25 mL Schlenk flask containing a magnetic stirring bar were placed: DPND (0.1 mmol, 43.3 mg, 1.0 eq), tris(dibenzylideneacetone)dipalladium(0) (9.4 mg, 0.01 mmol, 10%mol), PCy3·HBF4 (7.2 mg, 0.02 mmol, 20%mol), pivalic acid (6.2 mg, 0.06 mmol, 60% mol), K2CO3 (55.2 mg, 0.4 mmol, 4.0 eq) and the haloarene 1a-d (0.3 mmol, 3.0 eq). The vessel was evacuated and backfilled with argon (3 times). Anhydrous, degassed toluene (2 mL) was added next using a syringe. The vessel was tightly closed and again carefully evacuated and backfilled with argon (3 times). The content of the flask was stirred at 120°C for typically 3-5 days. After indicated time the flask was cooled down to RT and extracted three times with dichloromethane (3 x 20 mL), then dried over magnesium sulphate. All solvents were evaporated off and the residue was purified by column chromatography. N,N'-((6,12-diheptyl-5,11-dioxo-5H,11H-dipyrrolo[1,2b:1',2'-g][2,6]naphthyridine-3,9-diyl)bis(2,1-phenylene))diacetamide (2a). Prepared using N-(2-bromophenyl)acetamide16a (64.2 mg, 0.3 mmol). Product was purified using column chromatography (SiO2, hexanes : ethyl acetate, 1:1) and recrystallized from MeCN to give 20.5 mg (29% yield) of product. Rf = 0.17 (SiO2, hexanes/ethyl acetate, 1:1). mp. 208 - 209°C. 1H NMR (500 MHz, acetone-d6) δ 8.49 (s, 2H), 8.13 (br s, 2H), 7.37 (t, 2H, J = 7.0 Hz), 7.30 (d, 2H, J = 7.0 Hz), 7.14 (m, 2H), 7.12 (d, 2H, J = 3.5 Hz), 6.58 (d, 2H, J = 4.0 Hz), 3.26-3.10 (m, 4H), 1.91 (s, 6H), 1.67-1.61 (m, 4H), 1.47-1.41 (m, 4H), 1.361.27 (m, 12H), 0.86 (t, 6H, J = 7.0 Hz). Compound is too insoluble to record a 13C NMR spectrum. HRMS (ESI) calcd for C44H50N4O4Na 721.3730 [M+Na+], found 721.3710. N,N'-((6,12-diheptyl-5,11-dioxo-5H,11H-dipyrrolo[1,2b:1',2'-g][2,6]naphthyridine-3,9-diyl)bis(5-(trifluoromethyl)-2,1-phenylene))diacetamide (2b). Prepared using N-(2bromo-5-(trifluoromethyl)phenyl)acetamide16b (84.6 mg, 0.3 mmol). Product was purified using column chromatography (SiO2, hexanes : ethyl acetate, 1:1 to 2:3) and recrystallized from cyclohexane to give 44.7 mg (53% yield) of product. Rf = 0.28 (SiO2, hexanes/ethyl acetate, 1:1). mp. 219 - 220°C. 1H NMR (500 MHz, acetone-d6) δ 8.81 (s, 2H), 8.46 (br s, 2H), 7.71 (d, 2H, J = 9.0 Hz), 7.62 (s, 2H), 7.17 (d, 2H, J = 4.0 Hz), 6.73 (d, 2H, J = 3.5 Hz), 3.23-3.13 (m, 4H), 1.96 (s, 6H), 1.651.62 (m, 4H), 1.47-1.41 (m, 4H), 1.35-1.27 (m, 12H), 0.86 (t, 6H, J = 7.0 Hz). 13C NMR (125 MHz, acetone-d6) δ 168.2,



168.1, 158.9, 143.7, 140.7, 140.6, 135.2, 133.5, 127.4, 127.4, 125.3, 125.3, 124.5 (q, J(C, F) = 274.5 Hz), 124.1 (q, J(C, F) = 35.7 Hz), 119.4, 116.1, 116.0, 115.6, 31.6, 30.2, 30.1, 29.8, 23.4, 23.3, 22.4, 13.4. HRMS (ESI) calcd for C46H48N4O4F6Na 857.3477 [M+Na+], found 857.3471. N,N'-((6,12-diheptyl-5,11-dioxo-5H,11H-dipyrrolo[1,2b:1',2'-g][2,6]naphthyridine-3,9-diyl)bis(5-methoxy-2,1phenylene))diacetamide (2c). Prepared using N-(2-bromo-5methoxyphenyl)acetamide10a (73.2 mg, 0.3 mmol). Product was purified using column chromatography (SiO2, hexanes : ethyl acetate, 1:2). The residue after chromatography was boiled in minimal amount of cyclohexane, the flask was cooled down to room temperature, crystals were filtered off and dried to give 25.6 mg (34% yield) of product. R f = 0.31 (SiO2, hexanes/ethyl acetate, 1:2). mp. 215 - 217°C. 1H NMR (500 MHz, acetone-d6) δ 8.27 (br s, 2H), 7.85 (d, 2H, J = 9.0 Hz), 7.11 (d, 2H, J = 3.5 Hz), 6.94 (d, 2H, J = 9.0 Hz), 6.87 (br s, 2H), 6.56 (d, 2H, J = 3.0 Hz), 3.80 (s, 6H), 3.19-3.14 (br s, 4H), 1.85 (s, 6H), 1.661.60 (m, 4H), 1.46-1.41 (m, 4H), 1.34-1.28 (m, 12H), 0.86 (t, 6H, J = 7.0 Hz). 13C NMR (125 MHz, acetone-d6) δ 168.3, 159.8, 156.6, 136.6, 135.6, 128.5, 119.6, 116.8, 116.3, 115.9, 114.7, 79.2, 55.7, 32.5, 31.2, 30.9, 30.8, 23.8, 23.3. HRMS (ESI) calcd for C46H54N4O6Na 781.3941 [M+Na+], found 781.3934. N,N'-((6,12-diheptyl-5,11-dioxo-5H,11H-dipyrrolo[1,2b:1',2'-g][2,6]naphthyridine-3,9-diyl)bis(5-nitro-2,1-phenylene))diacetamide (2d). Prepared using N-(2-bromo-5-nitrophenyl)acetamide16c (77.7 mg, 0.3 mmol). Product was purified using column chromatography (SiO2, hexanes : ethyl acetate, 1:2). The residue after chromatography was boiled in minimal amount of cyclohexane for 5 min, the flask was cooled down to room temperature, the crystals were filtered off and dried to give 24.6 mg (31% yield) of product. Rf = 0.66 (SiO2, hexanes/ethyl acetate, 1:2). mp. 231 - 232°C. 1H NMR (500 MHz, acetone-d6) δ 9.02 (br s, 2H), 8.58 (dd, 2H, J1 = 4.0 Hz, J2 = 9.5 Hz), 8.28 (dd, 2H, J1 = 2.5 Hz, J2 = 9.5 Hz), 8.17 (br s, 2H), 7.20 (d, 2H, J = 3.5 Hz), 6.80 (d, 2H, J = 3.5 Hz), 3.33-3.07 (m, 4H), 1.99 (s, 6H), 1.67-1.61 (m, 4H), 1.44-1.40 (m, 4H), 1.33-1.26 (m, 12H), 0.85 (t, 6H, J = 7.0 Hz). 13 C NMR (125 MHz, acetone-d6) δ 168.6, 168.5, 158.9, 144.0, 143.4, 143.3, 142.4, 135.4, 132.5, 125.8, 125.1, 125.0, 123.9, 121.0, 120.9, 119.7, 116.3, 115.7, 31.6, 30.1, 30.1, 29.8, 23.6, 23.5, 22.4, 13.4. HRMS (ESI) calcd for C44H48N6O8Na 811.3431 [M+Na+], found 811.3416. General procedure for the synthesis of dyes 3a-3c. In a 100 mL round-bottom pressure flask containing a magnetic stirring bar were placed: 2a-d (0.07 mmol), HClconc or HClconc/H2SO4 conc, and 40 mL of MeOH. The flask was tightly closed and the content of the flask was stirred at 80°C for 3048h. After indicated time the flask was cooled down to RT and the content of the flask was slowly added to the solution of NaOH (1.1 eq of NaOH versus molar equivalent of H+) dissolved in ~100 mL of water. The solid was filtered off, washed with water and minimal amount of cold methanol. Then the crude material was adsorbed onto Celite and purified using column chromatography. All further manipulations are described below. 7,15-diheptylquinazolino[4'',3'',2'':3',4',5']indolizino[7',6':6,7]indolizino[5,4,3-bc]quinazoline (3a). Prepared using 2a (48.9 mg, 0.07 mmol) and 3 mL of concentrated HCl. Product was purified using column chromatography

(SiO2, CH2Cl2 : cyclohexane, 1:2). The residue after column was recrystallized from ethyl acetate, the crystals were filtered off and dried to give 31.6 mg (78% yield) of product. Rf = 0.59 (SiO2, CH2Cl2/cyclohexane, 1:2). mp. 247 - 248°C. 1H NMR (500 MHz, CDCl3, 50°C) δ 7.61 (d, 2H, J = 8.0 Hz), 7.45 (d, 2H, J = 8.0 Hz), 7.29 (t, 2H, J = 7.5 Hz), 7.23 (t, 2H, J = 7.5 Hz), 6.74 (m, 4H), 3.24-3.21 (m, 4H), 1.79-1.73 (m, 4H), 1.621.56 (m, 4H), 1.48-1.43 (m, 4H), 1.37-1.36 (m, 8H), 0.92 (t, 6H, J = 7.0 Hz). 13C NMR (125 MHz, CDCl3, 50°C) δ 142.9, 135.7, 128.4, 127.9, 126.9, 121.6, 121.4, 112.1, 102.6, 32.0, 30.5, 30.3, 29.3, 22.6, 14.0. HRMS (EI) calcd for C40H42N4 578.3409 [M·+], found 578.3409. 7,15-diheptyl-3,11-bis(trifluoromethyl)quinazolino[4'',3'',2'':3',4',5']indolizino[7',6':6,7]indolizino[5,4,3bc]quinazoline (3b). Prepared using 2b (58.4 mg, 0.07 mmol) and a mixture of 3 mL of concentrated HCl/1mL of concentrated H2SO4. Product was purified using column chromatography (SiO2, CH2Cl2 : cyclohexane, 1:2). The residue after column was recrystallized form ethyl acetate, the crystals were filtered off and dried to give 30.0 mg (60% yield) of product. mp. 253 - 254°C. Rf = 0.54 (SiO2, CH2Cl2/cyclohexane, 1:2). 1H NMR (500 MHz, tetrachloroethane-d2, 85°C) δ 7.82 (s, 2H), 7.49 (t, 4H, J = 7.0 Hz), 6.84 (d, 2H, J = 3.0 Hz), 6.82 (d, 2H, J = 3.0 Hz), 3.26-3.23 (m, 4H), 1.80-1.74 (m, 4H), 1.64-1.58 (m, 4H), 1.64-1.58 (m, 4H), 1.491.40 (m, 8H), 0.96 (t, 6H, J = 7.0 Hz). 13C NMR (125 MHz, tetrachloroethane-d2, 85°C) δ 146.0, 144.6, 136.8, 131.1, 128.8, 128.2 (q, J = 32.4 Hz), 127.6, 123.4 (q, J = 272.2 Hz), 120.9, 118.5 (q, J = 4.0 Hz), 118.0, 112.6, 103.5, 31.3, 30.1, 29.7, 28.7, 28.6, 22.0, 13.4. HRMS (EI) calcd for C 42H40N4F6 714.3157 [M·+], found 714.3152. 7,15-diheptyl-3,11-dimethoxyquinazolino[4'',3'',2'':3',4',5']indolizino[7',6':6,7]indolizino[5,4,3bc]quinazoline (3c). Prepared using 2c (53.1 mg, 0.07 mmol) and 1 mL of concentrated HCl. Product was purified using column chromatography (SiO2, cyclohexane : dichloromethane, 3:2). The residue after column was recrystallized from ethyl acetate, the crystals were filtered off and dried to give 16.4 mg (37% yield) of product. Rf = 0.26 (SiO2, CH2Cl2/cyclohexane, 2:3). mp. 216 - 217°C (dec.). 1H NMR (600 MHz, tetrachloroethane-d2, 100°C) δ 7.45 (d, 2H, J = 7.5 Hz), 7.08 (br s, 2H), 7.00-6.91 (br m, 2H), 6.826.70 (br m, 4H), 3.94 (s, 6H), 3.34-3.23 (m, 4H), 1.84-1.79 (m, 4H), 1.66-1.61 (m, 4H), 1.52-1.48 (m, 4H), 1.43-1.42 (m, 8H), 0.98 (t, 6H, J = 7.0 Hz). Due to profound molecular interactions in solution we were unable to record a 13C NMR signals coming from an aromatic part of molecule 3c even at 100°C. HRMS (EI) calcd for C42H46N4O2 638.3621 [M·+], found 638.3622.

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website. Copies of 1H NMR and 13C NMR spectra, cyclic voltammograms, computational details (PDF).

AUTHOR INFORMATION Corresponding Authors * E-mail: [email protected] * E-mail: [email protected]


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The Journal of Organic Chemistry ORCID Bartłomiej Sadowski: 0000-0002-1323-2826 David J. Stewart: 0000-0003-3246-3723 Tod Grusenmeyer: 0000-0002-1842-056X Daniel T. Gryko: 0000-0002-2146-1282

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 work was financially supported by the Polish National Science Centre (Grant No. PRELUDIUM 2016/23/N/ST5/00054). The authors would like to thank the Foundation for Polish Science (Grant TEAM/2016-3/22) and Global Research Laboratory Program (2014K1A1A2064569) through the National Research Foundation (NRF) funded by Ministry of Science, ICT & Future Planning (Korea). DJS acknowledges General Dynamics Information Technology contract FA8650-16-D-5402. ATP acknowledges SOCHE contract FA8650-14-2-5800.

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