All chemicals were purchased from Tokyo Chemical Industry Co., Wako Pure Chemical Industries Ltd, and Sigma-Aldrich, Japan. 1H NMR and 13C NMR spectra were recorded on a JEOL ECZ500 spectrometer, Bruker DPX-400 spectrometer, or Varian INOVA 400 spectrometer with chemical shifts recorded downfield from tetramethylsilane as the internal standard. Melting points were determined using a Mettler Toledo MP90 melting point apparatus equipped with a digital thermometer. Electrospray ionization high-resolution mass spectra were recorded on a JEOL AccuTOF-CS electrospray mass spectrometer. The molecular weights of the photoproducts were measured using GPC with SHIMADZU Prominence GPC equipped with both refractive index (RI) and ultraviolet (UV) detectors (UV detection, l = 280 nm) using Tosoh alpha 2000 columns. DMF containing 10 mM LiCl was used as the eluent. Transmission electron microscopy (TEM, JEM-1011, JEOL) at an accelerating voltage of 100 kV was used to observe the morphology of the self-assembly of each synthesized bolaamphiphile. The molecular weights of the photoproducts were analyzed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS; AUTOFLEX III, BRUKER). The photoproducts of bolaamphiphiles 1a and 1b after UV-light irradiation at 302 nm, which were corrected as a liquid by the evaporation of water, were dissolved in chloroform mixed with trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-propenylidene]malononitrile (DCTB) at a concentration of 10 mg/mL as a matrix.

Fluorescence spectrometers (FP-6500, JASCO) were used to determine the Critical Aggregation Concentration (CAC) using pyrene as the probe. A pyrene solution (6.0 × 10–2 M) was prepared by dissolving in acetone and diluting this solution with water. The acetone in the solution mixture was evaporated to form an acetone-free pyrene solution with a final concentration of 12.0 × 10–7 M. The pyrene solution was added to each bolaamphiphile solution (2 mL) with concentrations ranging from 6.3 × 10–6 to 1.3 × 10–2 M for the ester-bonded bolaamphiphiles 1a and 1b, respectively. To determine the CAC, the ratio of the fluorescence intensity of the first peak at ~ 372 nm (I1) to that of the third peak at ~ 385 nm (I3) was plotted as a function of the log[concentration] of the bolaamphiphiles. The intersection of the approximate curves of the high- and low-concentration regions was defined as the CAC [27, 28].

Bolaamphiphiles 1a and 1b were dissolved in pure water at a concentration of 1.8 × 10–3 M. The solutions were heated for 1 h at 70 °C and allowed to cool to RT (25 °C) for 3 weeks except for the Critical aggregation concentration measurement and gel permeation chromatography, for which self-assembled bolaamphiphiles were prepared by sonication for 1 h without the process of heating and cooling.

Bolaamphiphiles were dispersed in water at a concentration of 1.8 × 10–3 M and filled into quartz cuvettes with a screw cap. The cuvettes were placed in a UV crosslinker (CL1000M, UVP) and irradiated for several hours with a lamp that produced mid-range UV light at wavelengths centered at 302 nm which extends from 280 to 320 nm. Photochemical reactions were traced using a UV–Vis spectrometer (V-550, JASCO). The samples for UV/Vis measurements were diluted because the absorbance of the solution was saturated at a concentration of 1.8 × 10–3 M.

The self-assembled structures of bolaamphiphiles 1a and 1b were simulated by molecular mechanics (MM) molecular modeling on BIOVIA Materials Studio 2019 using the Forcite geometry optimization module with a DREIDING force field. A pair of 1a and 1b molecules was placed in a unit cell and calculated under periodic boundary conditions. Repeating structures were visualized using the Mercury CSD 4.3.1 software.

Dimethyl 3,3′-(3,3′-(butane-1,4-diyl)bis(5-methyl-2,4-dioxo-3,4-dihydropyrimidine-3,1(2H)-diyl))dipropanoate (3), methyl 3-phenyl)methyl]-5-methyl2,4-dioxo-1,2,3,4-tetrahydropyrimidin-1-yl}propanoate (4a), methyl 3- phenyl) methyl]-5-methyl2,4-dioxo-1,2,3,4-tetrahydropyrimidin-1-yl}propanoate (4b), and methyl 3-phenyl)methyl]-5-methyl-2,4-dioxo1,2,3,4-tetrahydropyrimidin-1-yl}propanoate (4c) were synthesized according to previously reported procedures [22, 24].

3,3′-((1,2-phenylenebis(methylene))bis(5-methyl-2,4-dioxo-3,4-dihydropyrimidine-3,1(2H)-diyl))dipropionic acid (5a): NaOH aqueous solution (2%, 300 mL) and 4a (3.00 g, 5.70 mmol) were added to a 300 mL round-bottom flask with stirring. The mixture was then refluxed for 1 h. The reaction mixture was acidified by adding concentrated aqueous HCl solution. The mixture was then placed in an ice bath for 2 h to precipitate a white solid. After filtering the solids, the filtrate was stored at RT for recrystallisation. After filtration, the white solid obtained was washed twice with cold distilled water to obtain 5a. Yield 1.07 g, 38%. M.P. 140.7–142.2 °C. 1H NMR (400 MHz, DMSO, δ) 1.84 (s, 6H), 2.62–2.68 (t, J = 4.0 Hz, 4H), 3.93 (t, J = 4.1 Hz, 4H), 5.15 (s, 4H), 6.84−6.92 (m, 2H), 7.10–7.16 (m, 2H), 7.67–7.71 (m, 2H), 12.44 (s, 2H). 13C NMR (100 MHz, CDCl3, δ) 13.01, 31.24, 33.24, 36.24, 39.39, 39.60, 39.80, 40.01, 40.22, 40.42, 40.63, 41.39, 107.82, 125.90, 127.26, 134.74, 141.44, 151.37, 162.75, 163.63, 172.71. High-resolution mass spectroscopy (electrospray ionization) [HRMS(ESI)] m/z [M + Na]+ calculated for C24H26N4O8 + Na+: 521.1646; found: 521.1643.

3,3′-((1,3-phenylenebis(methylene))bis(5-methyl-2,4-dioxo-3,4-dihydropyrimidine-3,1(2H)-diyl))dipropionic acid (5b): NaOH aqueous solution (2%, 100 mL) and 4b (1.0 g, 3.13 mmol) were added to a 250 mL round-bottom flask with stirring. The mixture was then refluxed for 1 h. The reaction mixture was acidified by adding concentrated aqueous HCl solution. The reaction mixture was placed at 4 °C to precipitate a white solid as a pure titled compound. Yield 0.820 g, 87%. M.P. 239.5–244.0 °C. H NMR (400 MHz, DMSO, δ) 1.80 (s, 6H), 2.61–2.66 (t, J = 4.0 Hz, 4H), 3.86–3.94 (t, J = 4.1 Hz, 4H), 4.95 (s, 4H), 7.14–7.24 (m, 4H), 7.60–7.66 (s, 2H), 12.44 (a, 2H). 13C NMR (100 MHz, CDCl3, δ) 13.06, 33.20, 39.37, 39.58, 39.79, 40.00, 40.20, 40.41, 40.62, 43.98, 45.55, 107.84, 126.57, 127.05, 128.74, 137.72, 141.26, 151.28, 163.47, 172.71. HRMS(ESI) m/z [M + Na] + calculated for C24H26N4O8 + Na +  521.1646; found: 521.1643.

3,3′-((1,4-phenylenebis(methylene))bis(5-methyl-2,4-dioxo-3,4-dihydropyrimidine-3,1(2H)-diyl))dipropionic acid (5c): NaOH aqueous solution (2%, 100 mL) and 4c (1.0 g, 3.13 mmol) were added to a 250 mL round-bottom flask with stirring. The mixture was then refluxed for 1 h. The reaction mixture was acidified by adding concentrated aqueous HCl solution. The reaction mixture was placed at 4 °C to precipitate a white solid as a pure title compound. Yield 0.35 g, 64%. M.P. 239.5–244.0 °C. H NMR (400 MHz, DMSO, δ) 1.80 (s, 6H), 2.63 (t, J = 3.8 Hz, 4H), 3.89 (t, J = 3.9 Hz, 4H), 4.95 (s, 4H), 7.16–7.20 (m, 4H), 7.61 (m, 2H), 12.40(s, 1.6H). 13C NMR (100 MHz, CDCl3, δ) 13.06, 33.20, 39.37, 39.58, 39.79, 40.00, 40.20, 40.41, 40.62, 43.98, 45.55, 107.84, 126.57, 127.05, 128.74, 137.72, 141.26, 151.28, 163.47, 172.71. HRMS(ESI) m/z: [M + Na]+ calculated for C24H26N4O8 + Na+ 521.1643; found 521.1636.

3,3′-((1,2-phenylenebis(methylene))bis(5-methyl-2,4-dioxo-3,4-dihydropyrimidine-3,1(2H)-diyl))bis(N-(2-(2-(2-methoxyethoxy)ethoxy)ethyl)propanamide)(1a): 5a (0.357 g, 0.72 mmol) and 1-hydroxybenzotriazole monohydrate (HOBt; 0.246 g, 1.6 mmol) were dissolved in DMF (15 mL) in a round-bottom flask placed in an ice bath. While stirring, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (0.304 g, 1.6 mmol) was added to the mixture, followed by the addition of TEGNH2 (0.273 g, 1.7 mmol). After stirring for 2 h in an ice bath, the reaction was allowed to proceed at RT for 2 d. The mixture was evaporated to remove DMF. The residue was taken up in CH2Cl2, washed with a saturated aqueous NaHCO3 solution (3 × 100 mL) and brine with low pH adjusted with concentrated HCl, and dried over MgSO4. After filtration, the filtrate was evaporated to obtain a brownish, viscous residue. The crude product was purified by column chromatography (chloroform:methanol:ethyl acetate = 5:1:3) to yield the pure product. Yield 0.518 g, 92%. 1H NMR (500 MHz, CDCl3, δ) 1.92 (s, 6H), 2.58–2.64 (t, J = 5.8 Hz, 4H), 3.35 (s, 6H), 3.37–3.34 (m, 3H), 3.47–3.63 (m, 21H), 4.00–4.06 (t, J = 6.0 Hz, 4H), 5.42 (s, 4H), 6.51–6.57 (t, J = 5.3 Hz, 2H), 7.13 − 7.25 (m, 6H). 13C NMR (125 MHz, CDCl3, δ 13.10, 34.85, 39.37, 41.88, 46.43, 58.96, 70.15–71.85, 109.28, 127.40, 128.47, 135.06, 140.10, 151.60, 164.05, 170.06. HRMS(ESI) m/z [M + Na]+ calculated for C38H56N6O12 + Na+ 788.3956; found 811.3845.

3,3′-((1,3-phenylenebis(methylene))bis(5-methyl-2,4-dioxo-3,4-dihydropyrimidine-3,1(2H)-diyl))bis(N-(2-(2-(2-methoxyethoxy)ethoxy)ethyl)propanamide) (1b): The titled compound was synthesized and purified following the same procedure as that followed for 1a. Yield 0.856 g, 70%. 1H NMR (500 MHz, CDCl3, δ) 1.87 (s, 6H), 2.65–2.68 (t, 5.8 Hz, 4H), 3.34 (s, 6H), 3.35–3.56 (m, 24H), 4.02–4.05 (t, J = 6.0 Hz, 4H), 5.06 (s, 4H), 7.02–7.04 (t, J = 5.3 Hz, 2H), 7.17 − 7.24 (m, 3H), 7.30–7.35 (m, 3H).13CDCl3 (125 MHz, CDCl3, δ) 12.98, 34.72, 39.41, 44.30, 46.63, 58.97, 69.63–71.86, 109.32, 128.13, 137.26, 140.20, 163.66, 170.11. HRMS(ESI) m/z [M + Na]+ calculated for C38H56N6O12 + Na+ 788.3956; found 811.3842.

3,3′-((1,4-phenylenebis(methylene))bis(5-methyl-2,4-dioxo-3,4-dihydropyrimidine-3,1(2H)-diyl))bis(N-(2-(2-(2-methoxyethoxy)ethoxy)ethyl)propanamide) (1c): The titled compound was synthesized and purified following the same procedure as that followed for 1a. Yield: 0.839 g, 70%. 1H NMR (500 MHz, CDCl3, δ) 1.88 (s, 6H), 2.55–2.61 (t, J = 5.8 Hz, 4H), 3.34 (s, 6H), 3.40–3.42 (m, 10H), 3.48–3.55(m, 8H), 3.58–3.62 (m, 12H), 3.92–4.01 (t, 4H), 5.06 (s, 4H), 6.32–6.36 (t, J = 5.3 Hz, 2H), 7.18–7.21 (m, 2H), 7.37–7.39 (m, 4H). 13CDCl3 (125 MHz, CDCl3, δ) 0.06, 13.07, 14.28, 34.83, 39.45, 44.25, 46.25, 59.03, 70.23, 70.46, 70.54, 71.94, 76.85, 77.10, 77.35, 109.42, 129.21, 136.34, 140.06, 151.60, 163.87, 170.02. HRMS(ESI) m/z [M + Na]+ calculated for C38H56N6O12 + Na+ 811.3848; found 811.382.