Synthesis, photophysical properties and solvatochromic analysis of some naphthalene-1,8-dicarboxylic acid derivatives

Journal Pre-proof Synthesis, photophysical properties and solvatochromic analysis of some naphthalene-1,8-dicarboxylic acid derivatives

Alina Nicolescu, Anton Airinei, Emilian Georgescu, Florentina Georgescu, Radu Tigoianu, Florin Oancea, Calin Deleanu PII:

S0167-7322(19)36405-0

DOI:

https://doi.org/10.1016/j.molliq.2020.112626

Reference:

MOLLIQ 112626

To appear in:

Journal of Molecular Liquids

Received date:

1 December 2019

Revised date:

21 January 2020

Accepted date:

30 January 2020

Please cite this article as: A. Nicolescu, A. Airinei, E. Georgescu, et al., Synthesis, photophysical properties and solvatochromic analysis of some naphthalene-1,8-dicarboxylic acid derivatives, Journal of Molecular Liquids(2018), https://doi.org/10.1016/j.molliq.2020.112626

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© 2018 Published by Elsevier.

Journal Pre-proof Synthesis, photophysical properties and solvatochromic analysis of some naphthalene1,8-dicarboxylic acid derivatives

Alina Nicolescu

a,b

, Anton Airinei a,*, Emilian Georgescu c, Florentina Georgescu d, Radu

Tigoianu a, Florin Oancea e, Calin Deleanu a,b,* a

“Petru Poni” Institute of Macromolecular Chemistry, Romanian Academy, Aleea Grigore

Ghica Voda 41A, RO-700487 Iasi, Romania b

“C. D. Nenitescu” Centre of Organic Chemistry, Romanian Academy, Spl. Independentei

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202B, RO-060023 Bucharest, Romania

Chimcomplex Research Center, St. Uzinei 1, RO-240050 Ramnicu Valcea, Romania

d

Enpro Soctech Com srl, Str. Elefterie 51, RO-050524 Bucharest, Romania

e

National Research & Development Institute for Chemistry & Petrochemistry – ICECHIM,

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ro

c

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Spl. Independentei 202, RO-060021 Bucharest, Romania

ABSTRACT

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Two groups of new naphthalene-1,8-dicarboxylic acid derived compounds, 6-amino-1,8naphthalic anhydride derivatives and 2-hydroxy-6-amino-1,8-naphthalimide derivatives, have

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been synthesized and characterized. The spectroscopic properties of all synthesized compounds were investigated in order to be used in the field of bio-imaging studies and as

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intermediates for the preparation of new fluorescent bioactive compounds. Positive solvatochromism was observed from non-polar to polar solvents and it was discussed using

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Catalan multilinear regression analysis. Comparative study of the photophysical characteristics of naphthalic anhydride and 1,8-naphthalimide derivatives was performed. The new naphthalic anhydride 6-(4-benzyl-piperazin-1-yl)benzo[de]isochromene-1,3-dione (3) presents the highest value of fluorescence quantum yield in solvents with lower polarities. The results demonstrate that the quantum yields values of naphthalic anhydride derivatives are higher than those of naphthalimide derivatives.

Keywords: spectroscopic properties; fluorescence; 1,8-naphthalic anhydride derivatives; 1,8naphthlimide derivatives, quantum yield; NMR

* Corresponding authors: E-mail address: [email protected] (A. Airinei). 1

Journal Pre-proof E-mail address: [email protected] (C. Deleanu).

1. Introduction Fluorescence has become an important method used in biotechnology, medicinal chemistry and clinical diagnostics because it offers high sensitivity and selectivity, noninvasive, real-time monitoring, rapid response and low detection limits. Fluorescent compounds have broad range of applications as key tools for chemical biology, as multipurpose dyes and photoelectric materials [1,2]. Organic fluorophores based on a naphthalene nucleus are known as dyes, fluorescent sensors and fluorescent probes [3-6].

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Compounds containing 1,8-naphthalimide nucleus have found applications as fluorescent dyes for fibers [7-10], liquid-crystal displays [11], optical brighteners [12], photoinduced

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electron transfer (PET) fluorescent sensors [13-17], and fluorescent molecular probes [18-22].

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Many of 1,8-naphthalimide derivatives have interesting biological properties and applications [23,24]. Usually, 1,8-naphthalic anhydride derivatives are prepared by the interaction of 4-

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nitro- or 4-halo-1,8-naphthalic anhydride with secondary amines in various reaction conditions [7,8,13,22], while 1,8-naphthalimide derivatives are synthesized by the reaction of

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4-nitro- or 4-halo-1,8-naphthalic anhydride with hydroxylamine or primary amines in a large variety of solvents and reaction conditions [7-9,18].

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Continuing our researches in the field of bioactive compounds [24-31], we investigated a range of naphthalene-1,8-dicarboxylic acid derived compounds which are to be

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used for bio-imaging investigations and intermediates for the preparation of new fluorescent bioactive compounds. Herein we report the synthesis, characterization and spectroscopic

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properties of two groups of 6-amino-1,8-naphthalic anhydride derivatives and 2-hydroxy-6amino-1,8-naphthalimide derivatives.

2. Experimental 2.1. Methods Melting points were determined on a Boetius apparatus and are uncorrected. The IR spectra were recorded on a Nicolet Impact 410 spectrometer, in KBr pellets. The NMR analyses were performed on Bruker Avance Neo spectrometers, operating either at 400.1, 100.6 and 40.6 MHz for 1H, 13C, and 15N respectively, or at 600.1, 150.9, and 60.8 MHz for 1

H, and

13

C, and

15

N respectively. The 1D and 2D spectra were recorded with 5 mm

multinuclear inverse detection z-gradient probes. Unambiguous 1D NMR signal assignments were made based on 2D NMR homo- and heteronuclear correlations. H-H COSY (Correlation 2

Journal Pre-proof Spectroscopy), H-C HSQC (Heteronuclear Single Quantum Coherence) and H-C HMBC (Heteronuclear Multiple Bond Correlation) experiments were recorded using standard pulse sequences in the version with z-gradients, as delivered by Bruker with TopSpin 4.0.6 spectrometer control and processing software. Chemical shifts are reported in δ units (ppm) and were referenced to TMS for 1H nuclei (0.00 ppm), the residual solvent signals for

13

C

nuclei (CDCl3 at 77.0 ppm and DMSO-d6 at 39.4 ppm) and liquid ammonia (0.0 ppm) using nitromethane (380.2 ppm) as external standard for 15N nuclei. All reagents were commercially available products and have been used without purification. Exact molecular weights have been obtained from high resolution MS spectra recorded on a Bruker Maxis II QTOF

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spectrometer with electrospray ionization (ESI) in the positive mode excepting for one naphtalimide derivative (5) which could be ionized only in the negative mode.

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Ultraviolet-visible (UV-Vis) absorption spectra were determined on a SPECORD

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200PLUS Analytik Jena spectrophotometer in 10 mm quartz cuvettes. Steady state fluorescence measurements were obtained on a Perkin Elmer LS55 luminescence

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spectrometer using a four-side clear quartz cell with a path length of 10 mm at room temperature. The time resolved fluorescence spectra were collected on an Edinburgh FLS980

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spectrometer by using time-correlating single photon counting method. All emission decay profiles were determined in a 10 x 10 mm quartz cell, excited with a nanosecond diode laser

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operating at 375 nm as light source. For all the lifetime measurements the analysis of fluorescence decays was made by a multi-exponential model as in the following relation: I(t)

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= Σ aiexp(-t/τi), where I(t) represents the emission intensity at time t, ai and τi are the preexponential factor and the decay time of component i, respectively. The best fitted parameters

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were obtained for reduced chi-squared values close to 1 and the weighted residuals were uniform distributed around zero line. The fluorescence quantum yields were measured on a FSL980 luminescence spectrometer using an integrating sphere on dilute solutions with an absorbance below 0.1 at the excitation wavelengths corresponding to the absorption maxima.

2.2. Synthetic procedures 2.2.1. General procedure for the synthesis of 4-amino-1,8-naphthalic anhydrides (2-4) To a suspension of 3.5 g (15 mmol) 4-chloro-1,8-naphthalic anhydride (1) in 50 mL of N-methylpyrrolidone 20 mmol of cyclic secondary amine and 3.5 mL (25 mmol) of triethylamine were added and the reaction mixture was heated at reflux temperature for 24 hour. The most part of the solvent was distilled under vacuum, 100 mL of water was added under stirring and the reaction product extracted in chloroform (3 x 150 mL). Combined 3

Journal Pre-proof extracts were dried on Na2SO4 anh., the solvent was distilled off and the residue was triturated with acetone, the solid filtered off and recrystallized from EtOH.

6-(4-Methyl-piperidin-1-yl)benzo[de]isochromene-1,3-dione (2). Orange crystals (3.63 g, 82%) with mp. 153-155 °C. 1H-NMR (600.1 MHz, DMSO-d6, δ ppm): 1.04 (3H, d, J = 6.5 Hz, CH3), 1.48-1.55 (2H, m, CH2-3‟A), 1.61-1.68 (1H, m, CH-4‟), 1.83 (2H, dd, J = 12.5, 2.0 Hz, CH2-3‟B), 2.96 (2H, td, J = 12.1, 1.7 Hz, CH2-2‟A), 3.58 (2H, d, J = 12.4 Hz, CH2-2‟B), 7.30 (1H, d, J = 8.2 Hz, CH-5), 7.80 (1H, t, J = 7.3 Hz, CH-8), 8.36 (1H, d, J = 8.2 Hz, CH4), 8.42 (1H, dd, J = 8.5, 1.0 Hz, CH-7), 8.46 (1H, dd, J = 7.3, 1.0 Hz, CH-9). 13C-NMR

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(150.9 MHz, DMSO-d6, δ ppm): 21.7 (CH3), 30.2 (CH-4‟), 33.8 (CH2-3‟), 53.0 (CH2-2‟), 110.4 (C-3a), 115.1 (CH-5), 119.1 (C-9a), 125.1 (C-6a), 126.0 (CH-8), 131.7 (C-9b), 131.9

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(CH-7), 132.4 (CH-9), 134.2 (CH-4), 157.3 (C-6), 160.3 (CO-3), 161.2 (CO-1).

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N-NMR

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(60.8 MHz, DMSO-d6, δ ppm): 76.0 (N-1‟). IR (KBr, cm-1): 2937, 1766, 1719, 1586, 1565, 1515, 1455, 1395, 1325, 1299, 1226, 1116, 1079, 1015. HRMS-ESI (m/z): [M+H]+ for

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C18H18NO3, calcd. 296.1281, found 296.1273.

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6-(4-Benzyl-piperidin-1-yl)benzo[de]isochromene-1,3-dione (3). Dark orange crystals (4.23 g, 76%) with mp. 195-197 °C. 1H-NMR (600.1 MHz, DMSO, δ ppm): 1.56-1.62 (2H, m,

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CH2-3‟A), 1.77-1.84 (3H, m, CH-4‟ and CH2-3‟B), 2.66 (2H, d, J = 7.0 Hz, CH2), 2.93 (2H, t, J = 12.1 Hz, CH2-2‟A), 3.62 (2H, d, J = 12.2 Hz, CH2-2‟B), 7.21 (1H, t, J = 7.4 Hz, CH-

ur

4”Ph), 7.25 (2H, d, J = 7.3 Hz, CH-2”Ph), 7.32 (2H, t, J = 7.6 Hz, CH-3”Ph), 7.33 (1H, d, J = 8.2 Hz, CH-5), 7.84 (1H, t, J = 7.60 Hz, CH-8), 8.40 (1H, d, J = 8.2 Hz, CH-4), 8.44 (1H, d, J

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= 8.5 Hz, CH-7), 8.50 (1H, dd, J = 7.2 Hz, CH-9). 13C-NMR (150.9 MHz, DMSO, δ ppm): 31.7 (CH2-3‟), 37.2 (CH-4‟), 42.2 (CH2), 53.0 (CH2-2‟), 110.5 (C-3a), 115.1 (CH-5), 119.2 (C-9a), 125.2 (C-6a), 125.9 (CH-4”Ph), 126.1 (CH-8), 128.3 (CH-3”Ph), 129.1 (CH-2”Ph), 131.8 (C-9b), 131.9 (CH-7), 132.4 (CH-9), 134.2 (CH-4), 140.0 (C-1”Ph), 157.3 (C-6), 160.4 (CO-3), 161.3 (CO-1). 15N-NMR (60.8 MHz, DMSO-d6, δ ppm): 75.6 (N-1‟). IR (KBr, cm-1): 2920, 2843, 1763, 1728, 1562, 1514, 1451, 1377, 1305, 1229, 1179, 1080, 1017. HRMS-ESI (m/z): [M+Na]+ for C24H21NO3Na, calcd. 394.1414, found 394.1429. 6-(4-Methyl-piperazin-1-yl)benzo[de]isochromene-1,3-dione (4). The preparation of this compound was already reported [28] but without separation and characterization. Pale yellow crystals (3.15 g, 71%) with mp. 194-196 °C. 1H-NMR (600.1 MHz, DMSO, δ ppm): 2.31 (3H, s, CH3), 2.65 (4H, t, J = 4.1 Hz, CH2-3‟), 3.30 (4H, t, J = 4.4 Hz, CH2-2‟), 7.36 (1H, d, J 4

Journal Pre-proof = 8.2 Hz, CH-5), 7.84 (1H, t, J = 8.5 Hz, CH-8), 8.41 (1H, d, J = 8.2 Hz, CH-4), 8.48 (1H, dd, J = 8.5, 1.0 Hz, CH-7), 8.50 (1H, dd, J = 7.3, 1.0 Hz, CH-9). 13C-NMR (150.9 MHz, DMSO, δ ppm): 45.7 (CH3), 52.3 (CH2-2‟), 54.5 (CH2-3‟), 111.1 (C-3a), 115.2 (CH-5), 119.3 (C-9a), 125.1 (C-6a), 126.2 (CH-8), 131.7 (C-9b), 131.8 (CH-7), 132.5 (CH-9), 134.1 (CH-4), 156.6 (C-6), 160.3 (CO-3), 161.2 (CO-1).

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N-NMR (60.8 MHz, DMSO-d6, δ ppm): 36.6 (N-4‟),

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70.8 (N-1‟). IR (KBr, cm ): 2937, 2836, 2796, 1748, 1721, 1582, 1571, 1517, 1457, 1398, 1325, 1239, 1138, 1015. HRMS-ESI (m/z): [M+H]+ for C17H17N2O3, calcd. 297.1234, found 297.1246.

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2.2.2. General procedure for the synthesis of 2-hydroxy-4-amino-1,8-naphthalimide derivatives (5-8)

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To a suspension of 10 mmol of 1,8-naphthalic anhydride 1, 2, 3 or 4 in 35 mL of

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dioxane 1 g (14 mmol) of hydroxylamine hydrochloride and 2.76 g (20 mmol) of K2CO3 were added and the reaction mixture was heated at reflux temperature for 24 hour. The reaction

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mixture was poured on 100 g of crushed ice and neutralized with HCl 5%. The formed solid

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was filtered off, washed on the filter with water and acetone and recrystallized.

2-Hydroxy-6-(4-methyl-piperidin-1-yl)benzo[de]isoquinoline-1,3-dione 1

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crystals (2.83 g, 91%) with mp. 260-262 °C (from EtOH).

(5).

Orange

H-NMR (600.1 MHz,

DMSO+TFA, δ ppm): 1.00 (3H, d, J = 6.4 Hz, CH3), 1.47-1.55 (2H, m, CH2-3‟A), 1.59-1.63

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(1H, m, CH-4‟), 1.80 (2H, d, J = 11.0 Hz, CH2-3‟B), 2.90 (2H, t, J = 11.0 Hz, CH2-2‟A), 3.53 (2H, d, J = 12.1 Hz, CH2-2‟B), 7.29 (1H, d, J = 8.2 Hz, CH-5), 7.77 (1H, t, J = 7.50 Hz, CH-

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8), 8.39 (1H, d, J = 8.2 Hz, CH-4), 8.40 (1H, d, J = 8.4 Hz, CH-7), 8.48 (1H, d, J = 7.2 Hz, CH-9). 13C-NMR (150.9 MHz, DMSO+TFA, δ ppm): 21.8 (CH3), 30.5 (CH-4‟), 34.2 (CH23‟), 53.7 (CH2-2‟), 115.4 (CH-5), 115.6 (C-3a), 123.2 (C-9a), 126.0 (C-6a), 126.1 (CH-8), 128.5 (C-9b), 130.9 (CH-9), 131.1 (CH-7), 132.7 (CH-4), 157.1 (C-6), 160.4 (CO-3), 160.8 (CO-1). 15N-NMR (60.8 MHz, DMSO-d6, δ ppm): 71.1 (N-1‟). IR (KBr, cm-1): 3454, 2922, 2797, 1692, 1654, 1632, 1585, 1513, 1460, 1376, 1260, 1221, 1137, 1038. HRMS-ESI (m/z): [M-H]- for C18H17N2O3, calcd. 309.1234, found 309.1244. 2-Hydroxy-6-(4-benzyl-piperidin-1-yl)benzo[de]isochromene-1,3-dione crystals (2.91 g, 75%) with mp. 227-229 °C (from EtOH).

1

(6).

Orange

H-NMR (600.1 MHz,

DMSO+TFA, δ ppm): 1.54-1.60 (2H, m, CH2-3‟A), 1.74-1.76 (3H, m, CH-4‟ and CH2-3‟B), 2.62 (2H, d, J = 6.5 Hz, CH2), 2.83 (2H, t, J = 11.5 Hz, CH2-2‟A), 3.53 (2H, d, J = 11.7 Hz, 5

Journal Pre-proof CH2-2‟B), 7.17 (1H, t, J = 7.2 Hz, CH-4”Ph), 7.21 (2H, d, J = 7.1 Hz, CH-2”Ph), 7.26 (1H, d, J = 8.0 Hz, CH-5), 7.28 (2H, t, J = 7.5 Hz, CH-3”Ph), 7.77 (1H, t, J = 7.8 Hz, CH-8), 8.36 (1H, d, J = 8.2 Hz, CH-4), 8.38 (1H, d, J = 7.0 Hz, CH-7), 8.46 (1H, d, J = 7.1 Hz, CH-9). 13

C-NMR (150.9 MHz, DMSO+TFA, δ ppm): 32.1 (CH2-3‟), 37.6 (CH-4‟), 42.6 (CH2), 53.6

(CH2-2‟), 115.3 (CH-5), 115.6 (C-3a), 123.2 (C-9a), 125.9 (C-6a), 126.1 (CH-4”Ph and CH8), 128.4 (CH-3”Ph and C-9b), 129.3 (CH-2”Ph), 130.9 (CH-9), 131.1 (CH-7), 132.6 (CH-4), 140.4 (C-1”Ph), 157.0 (C-6), 160.9 (CO-3), 161.2 (CO-1). 15N-NMR (60.8 MHz, DMSO-d6, δ ppm): 71.8 (N-1‟). IR (KBr, cm-1): 3451, 2918, 2801, 1702, 1663, 1585, 1513, 1456, 1376,

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1252, 1030. HRMS-ESI (m/z): [M+Na]+ for C24H22N2O3Na, calcd. 409.1523, found 409.1526. 2-Hydroxy-6-(4-methylpiperazin-1-yl)benzo[de]isoquinoline-1,3-dione (7) [32]. Orange

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crystals (2.64 g, 85%) with mp. 240-242 °C (from EtOH). 1H-NMR (600.1 MHz, DMSO, δ

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ppm): 2.46 (3H, s, CH3), 2.87 (4H, bs, CH2-3‟), 3.32 (4H, bs, CH2-2‟), 7.36 (1H, d, J = 8.2 Hz, CH-5), 7.82 (1H, t, J = 7.40 Hz, CH-8), 8.40 (1H, d, J = 8.2 Hz, CH-4), 8.45 (1H, d, J =

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8.5, CH-7), 8.48 (1H, d, J = 7.3 Hz, CH-9), 9.22 (1H, bs, OH).

13

C-NMR (150.9 MHz,

DMSO, δ ppm): 44.7 (CH3), 51.6 (CH2-2‟), 53.9 (CH2-3‟), 115.4 (CH-5), 115.9 (C-3a), 122.9

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(C-9a), 125.4 (C-6a), 126.2 (CH-8), 127.9 (CH-9b), 130.6 (CH-7), 130.7 (CH-9), 132.2 (CH4), 155.4 (C-6), 160.4 (CO-3), 160.8 (CO-1). 15N-NMR (60.8 MHz, DMSO-d6, δ ppm): 38.4

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(N-4‟), 65.8 (N-1‟). IR (KBr, cm-1): 3418, 2956, 2845, 1700, 1664, 1581, 1455, 1394, 1361,

found 312.1346.

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1230, 1193, 1149, 1029, 1008. HRMS-ESI (m/z): [M+H]+ for C17H18N3O3, calcd. 312.1343,

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2-Hydroxy-6-chloro-benzo[de]isoquinoline-1,3-dione (8). Dark beige crystals (2.3 g, 93%) with mp. 213-215 °C (from CHCl3/Et2O). 1H-NMR (400.1 MHz, DMSO, δ ppm): 8.00 (1H, t, J = 8.0 Hz, CH-8), 8.02 (1H, d, J = 7.8 Hz, CH-5), 8.43 (1H, d, J = 7.9 Hz, CH-4), 8.58 (2H, d, J = 7.9 Hz, CH-7 and CH-9), 10.84 (1H, s, OH). 13C-NMR (100.6 MHz, DMSO, δ ppm): 121.8 (C-3a), 123.1 (C-10), 127.3 (C-6), 127.8 (CH-5), 128.5 (C-6a), 128.7 (CH-8), 130.2 (CH-7), 130.9 (CH-4), 131.7 (CH-9), 137.7 (C-11), 160.1 (CO-3), 160.4 (CO-1). IR (KBr, cm-1): 3416, 3097, 2910, 1708, 1687, 1656, 1570, 1467, 1396, 1241, 1189, 1030. HRMS-ESI (m/z): [M+Na]+ for C12H6ClNO3Na, calcd. 269.9928, found 269.9940. HRMS-ESI (m/z): [M+H]+ for C12H7ClNO3, calcd. 248.0109, found 248.0120.

3. Results and discussion 3.1. Synthesis 6

Journal Pre-proof Two series of naphthalene-1,8-dicarboxylic acid derived compounds have been synthesized starting from commercially available 4-chloro-1,8-naphthalic anhydride 1. The first series, formally derived from 1,8-naphthalic anhydride, was prepared by treating 4chloro-1,8-naphthalic anhydride 1 in N-methylpyrrolidone with cyclic secondary amines such as 4-methylpiperidine, 4-benzylpiperidine and 4-methylpiperazine, respectively, to obtain the 4-amino-1,8-naphthalic anhydride derivatives 2-4, respectively (Scheme 1). The second series of compounds, formally derived from 1,8-naphthalimide, was prepared either by the reactions of 4-amino-1,8-naphthalic anhydride compounds 2-4 with hydroxylamine hydrochloride in dioxane, under basic conditions, to access the 2-hydroxy-4-amino-1,8-naththalimides 5-7

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respectively, or by the direct reaction of 4-chloro-1,8-naphthalic anhydride 1 with hydroxylamine hydrochloride to access 2-hydroxy-4-chloro-1,8-naphthalimide 8 (Scheme 1).

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The compounds 6-(4-methyl-piperazin-1-yl)benzo[de]isochromene-1,3-dione 4 and 2-

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hydroxy-6-(4-methylpiperazin-1-yl)benzo[de]isoquinoline-1,3-dione 7 have been previously prepared by different synthetic procedures, but no characterization data have been reported for

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the compound 4 while the compound 7 was only partly characterized [32]. All the other

R X

NH

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compounds are new, not previously reported in the literature. R X

Cl O O

2: R=Me, X=CH 3: R=benzyl, X=CH 4: R=Me, X=N

X

N N OH

K2CO3, 

O 5: R=Me, X=CH 6: R=benzyl, X=CH 7: R=Me, X=N

O

Cl

H2NOH HCl

N OH

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1

O

R

O

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O

H2NOH HCl

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

O

O

N

K2CO3, 

O 8

Scheme 1. The synthetic procedures towards naphthalene-1,8-dicarboxylic acid derivatives.

The structures of all synthesized compounds were assigned on the basis of chemical and spectral analysis (IR, 1H, and

13

C and

15

N NMR spectra). All 1H and

13

C NMR

assignments have been confirmed through 2D homo- and heteronuclear correlations. As a general trend, when comparing the NMR spectra for the transformation of anhydride group (from compounds 2, 3, 4) into hydroxypiperidinedione group (from compounds 5, 6, 7) there is almost no influence in the NMR spectra (less than 0.1 ppm variation in 1H chemical shifts and less than 1 ppm variation in

13

C chemical shifts) with the exception of the

7

13

C chemical

Journal Pre-proof shifts for positions 3a, 9a and 9b. Thus on the replacement of the O atom with N-OH group there is a 4 up to 5 ppm deshielding in positions 3a and 9a and a 3 ppm shielding in position 9b. Notably, even the two ketone groups in positions 1 and 2 directly linked to either O or NOH exhibit no noticeable chemical shifts differences. The molecular formula was confirmed in all cases through molecular ion detected by HR-MS. In all cases except compound 5 the compounds have been ionized either in positive mode (naphthalic anhydrides) or both in positive and negative modes (naphthalimides) whereas compound 5 revealed the molecular ion only in negative mode, i.e. by losing the proton attached to the imide group. The NMR

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and MS spectra for compounds 2-8 are presented as Supplementary Information.

3.2. Photophysical properties

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In view of future exploitation of synthesized compounds 2-8 in the field of bio-

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imaging investigations a study of the spectroscopic properties of these compounds has been undertaken. The UV-VIS absorption spectra of 1,8-naphthalic anhydride and 1,8-

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naphthalimide derivatives were recorded in solvents with different polarities and the spectral data are summarized in Table 1 and Table 2. The absorption spectra of the six derivatives (2-4

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and 5-7, respectively) are rather similar, having the main absorption band located at about 390-430 nm, depending on the solvent nature. Typical absorption spectra are shown in Fig. 1

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and Fig. 2 for naphthalic anhydride derivatives (2-4) and for naphthalimide derivatives (5-7), respectively. This absorption band from longer wavelengths can be assigned to a π-π*

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transition (first excited singlet, S1) [33-34] without vibrational structure. However, the presence of the methyl piperazine moiety in 4 and 7 determines a hypsochromic shift of the

Jo

absorption band around 403 nm as compared to the spectral profile of compounds 2, 3 and 5, 6 (Fig. 1 and 2). This blue shift can be caused by the decrease of coplanarity degree between the π electronic system of the naphthalene ring and the piperidine nitrogen. It is interesting to note that compounds 1 and 8 exhibit a different spectral pattern. In their electronic absorption spectra a broad absorption band with vibrational structure and a maximum around 340 was revealed (Fig. 1 and 2). The formation of the N-substituted derivatives by the reaction of 4chloro-1,8-naphthalic anhydride 1 is characterized by the appearance of a broad absorption band over 400 nm (Fig. 1) and the same spectral pattern was found for the naphthalimide derivatives 5-7 (Fig. 2). The absorption band from longer wavelengths of the derivatives 2-4 and 5-7 showed bathochromic shifts in function of the solvent polarity passing from a nonpolar to polar solvent (Table 1 and 2). As shown in Table 1, the absorption maximum of 2 shifted from 401 nm to 419 nm changing the solvent from toluene to DMSO. Unexpectedly, 8

Journal Pre-proof the absorption maximum for derivatives 2-4 and 5-7, respectively presents the highest red shift in dichloroethane as compared to a nonpolar solvent which is not adequated with the solvent polarity scale. The lowest red shifts were in compounds 1 and 8, suggesting a weak interaction between solute and solvent. Some fluorescence characteristics like Stokes shift (Δυ), emission wavelength (λ em), the quantum yield of fluorescence (Φ) and fluorescence lifetimes (τi) are presented in Tables 1-3. The emission bands of derivatives 2-4 and 5-7 appear in the green range at 530-545 nm, while the derivatives 1 and 8 demonstrates a violet emission at 380-410 nm (Fig. 3 and 4). Also, the presence of piperazine group in 4 and 7 indicates a slight shift to shorter

of

wavelengths of the emission maxima in the same manner as the electronic absorption spectra of 1 and 8. In Fig. 5, it can be noticed that the influence of the solvent polarity on the

ro

emission maxima is more pronounced as compared to absorption bands, the λem for 3 is

-p

shifted from 494 nm for toluene to 546 nm for DMSO. The significant red shift of the emission bands of derivatives 2-4 and 5-7 as the solvent polarity increases from non-polar to

re

polar solvents suggests that the excited state becomes highly polar and it is stabilized with increasing solvent polarity.

lP

The fluorescence quantum yields of the naphthalic anhydride and naphtalimide series were determined in different solvents and the data were collected in Table 1 and 2. The results

na

revealed that the values of the fluorescence quantum yield depend strongly on the solvent polarity. The values of fluorescence quantum yield of the substituted naphthalic anhydrides

ur

are generally much higher than those of naphthalimide derivatives. As can be seen from Table 1, derivative 3 having a benzylpiperidine group exhibit the highest fluorescence quantum

Jo

yield in nonpolar or chlorinated solvents (Φdioxane = 69.24% and ΦDCM = 91.04%). The same observation is valid for derivative 2, but here the quantum yields are lower (Φdioxane = 56.91% and ΦDCM = 65.23%). At the same time, in polar solvents the fluorescence quantum yield dramatically diminishes (ΦCH3CN = 5.83% for 2 and ΦCH3OH = 0.53% for 3). This process can be related to the specific interaction in protic solvents or alcohols between carboxylic oxygen of naphthalic anhydride and solvent in terms of hydrogen bonds. These interactions can favor non-radiative transitions which cause the decrease of the fluorescence yield. Also, some deviations of the attached phenyl moieties out the plan of naphthalene structure can lead to the decrease of the emission quantum yield. This phenomenon was reported in other papers for naphthalic anhydride and naphthalimide derivatives [11,22], which is in accordance with our experimental data. We can notice that the quantum yields of the derivatives 4 and 7 containing piperazine moiety were 5.87 and 4.67, respectively, in toluene, while in DMF the 9

Journal Pre-proof values of the quantum yield were 5.59 and 0.01, respectively. The fluorescence quantum yields of naphthalimide derivatives respect practically the same characteristics found to the naphthalic anhydride derivatives. Representative

time-resolved

decay

profiles

of

naphthalic

anhydride

and

naphthalimide derivatives are presented in Fig. 6 and the relevant results are collected in Table 3. Also, a strong solvent influence on the photophysical properties of compounds 2-4 and 5-7 was observed. For the naphthalimide derivatives, a monoexponential decay of the fluorescence lifetime was observed in non-polar solvents, while in polar solvents a biexponential decay was found out. For the naphthalic anhydride derivatives, the decay

of

profiles were adjusted to a biexponential model, excepting DMF where three fluorescence lifetimes were found out. The values of fluorescence lifetime decrease significantly passing

ro

from a nonpolar solvent to a polar one. In all cases, for the biexponential decay, it is clear that

-p

the lifetime τ1 is lower than τ2 for a particular solvent. The emission lifetime in non-polar solvents was around 9 ns for compounds 2-4 and 4.5-7.0 ns for compounds 5-7. The emission

re

decay in polar solvents supposes a biexponential fitting of the experimental data associated with two lifetimes τ1 and τ2. For both derivative series τ1 is lower than τ2 and the contributions

na

3.3. Solvatochromic behavior

lP

of the two lifetime components are much higher for τ1 than for τ2 (Table 3).

The solvent effect on the absorption and emission bands of some naphthalimide and

ur

naphthal anhydride derivatives was analyzed using the Catalan solvatochromic model [35,36] and a model based on the following solvatochromic parameters: polarity function f(ε) = ε +

Jo

1/ε + 2, electronic polarizability f(n) = (n2 – 1)/ (n 2 + 2), H-bonding donor ability (α) and Hbonding acceptor ability (β) [37,38], according to the relations: υ = υ0 + asaSA + bSBSB + cSPSP + dSaPSdP

(1)

and υ = υ0 + C1f(ε) + C2f(n) + C3β + C4α

(2)

where υ0 denotes the extrapolated value of wavenumber in gas state, SA is the solvent acidity, SB represents the solvent basicity, SP is the solvent polarizability, SdP denotes the solvent dipolarity, aSP, bSP, cSP, dSP and C1, C2, C3, C4 are coefficients which are characteristic for a given compound. For a certain solvent υ and υ0 represent the studied spectral property (υabs, υem, Δυ) in the presence or in the absence of the solvent. The values of the solvatochromic parameters [35,36,39-42] are given in Table 4. The regression coefficients indicate the dependence of y on the solvent parameters. The multiparametric regression analysis for the 10

Journal Pre-proof absorption and emission band maxima and Stokes shifts was performed using equations (1) and (2) to explain the solvato(fluoro)chromism of the these naphthalimide derivatives. The resulting values for the regression coefficients and the correlation coefficient (R2) for absorption and emission bands and Stokes shift are given in Table 5. The two types of multilinear regressions according to equations (1) and (2) give practically similar trends with high R2 values, suggesting a significant contribution of the non-specific interactions on the solvatochromic shifts. Plots corresponding to the calculated data according to equation (1) as a function of the experimental data are depicted in Fig. 7. It can be noticed from Table 5 that the

of

nonspecific interactions are the most important in the dependence of υ a and υem on Catalan parameters. The multilinear regression using the Catalan parameters indicates that the

ro

absorption maxima are mainly determined by the polarizability coefficient, however, the

-p

solvent dipolarity cannot be neglected for derivatives 2 and 3, and the basicity becomes a major contributor for derivatives 5 and 6, taking into account the values of the corresponding

re

coefficients. The dependence of Stokes shifts (Δυ) on the Catalan parameters indicated that the solvent polarizability and basicity had also a high influence on the Δυ for all derivatives

lP

being less sensitive to solvent dipolarity. As given in Table 5 the solvent polarizability contributions are of three magnitude orders higher relating to the basicity contribution. For the

na

fluorescence spectra the non-specific contributions represented by the polarizability and dipolarity coefficients give the greatest contribution to the spectral shifts. The negative sign of

ur

regression coefficients cSP and aSP is consistent with the bathochromic shift of the emission polar one.

Jo

maxima and the change in fluorescence quantum yield values from a nonpolar solvent to a The estimated coefficients using the {f(n), f(ε), β, α} multilinear regression analysis are listed in Table 5. In this case the changes in the absorption and fluorescence spectra of compounds 2,3 and 4,5 following the equation (2), the coefficients of polarizability (C2) and dielectric function (C2) are much higher than those of basicity and acidity suggesting that these compounds are more sensitive to the polarizability and induction interactions (f(ε)). The |C3| values are higher than |C4| excepting derivatives 4,5 for emission spectra. The {f(n), f(ε), β, α} multilinear regression fit applied to Δυ evolution showed again that the spectral shifts are dependent mainly on the polarizability (f(n) function) and solvent basicity because the absolute values of coefficient C2 is bigger than C3 coefficient and we must admit that the Stokes shifts are less sensitive to orientation-induction interactions and solvent acidity. A

11

Journal Pre-proof good agreement between the experimental data and wavenumbers determined according equations (1) and (2) was found in the selected solvents (Fig. 7 and 8). Due to their excellent emission properties some naphthalimide derivatives have been tested as chemosensors for different metal ions or neutral molecules [43,44]. For this purpose the emission characteristics of naphthalic anhydride and naphthalimide derivatives were investigated to detect picric acid. Firstly, fluorimetric titration was performed with compound 2 in presence of different concentrations of picric acid (c0 = 1.003x10-4 mol/L) in DMF. When the picric acid solution was gradually added into the solution of derivative 2, the fluorescence intensity decreases without the change of the position and the spectral profile, as shown in

of

Fig. 9. The quenching efficiency can be estimated using the relation (I0-I)/I0 where I0 and I are the fluorescence intensities before and after addition of picric acid as quencher. The

ro

fluorescence quenching efficiency reaches around 42 % for derivatives 2 and 3, respectively

-p

and 48 % for 5 and 6. A higher quenching efficiency was obtained for derivative 1 (33 %). The fluorescence quenching due to picric acid can be described by the Stern-Volmer (SV)

re

equation:

I0/I = 1 = KSV[C]

(3)

lP

where I0 and I are the fluorescence intensity in the absence and in the presence of quencher, [C] is the molar concentration of quencher and KSV represents the quenching constant. A good

na

linear relationship between I0/I ratio and quencher concentration was observed on the whole range of quencher concentration (Fig. 10). The Stern-Volmer constant calculated according to

ur

relation (3) was found to be 3.9x104 mol-1. The linearity of the Stern-Volmer plot indicated that the quenching can follow a static mechanism. The decrease of the emission lifetimes and

4. Conclusions

Jo

the quantum fluorescence yield can be associated with the increase of solvent polarity.

Synthesis procedures and photophysical properties for derivatives of 6-amino-1,8naphthalic anhydride and 2-hydroxy-6-amino-1,8-naphthalimide have been described. The results demonstrated that both 1,8-naphthalic anhydride and 1,8-naphthalimide derived group of compounds have fluorescence properties and convenient Stokes shift values. Multilinear regression analysis of these derivatives was carried out using Catalan solvatochromic parameters indicating that the solvent polarizability was a major factor responsible for the red shift of absorption and emission spectra. Also, the solvatochromic analysis based on {f(n), f(ε), β, α} parameters concluded that the polarity function and polarizability are the main contributors to the red shifted absorption and emission spectra from non-polar to polar 12

Journal Pre-proof solvents. Taking into account the discernible fluorescent characteristics of the naphthalic anhydride derivatives, their sensing properties towards picric acid were tested. Due to the interesting photophysical properties proved by some of these molecules, the design, synthesis and spectroscopic investigations of similar fluorescent compounds may be taken into consideration in bio-imaging investigations and as core of new fluorescent bioactive compounds.

Acknowledgements This work was supported by the Ministry of Research and Innovation, CNCS -

of

UEFISCDI, project ERANET-INCOMERA-2018-BENDIS within the PNCDI III and EU H2020 programs, Contract 7/2018. Access to research infrastructure developed in the “Petru

ro

Poni” Institute of Macromolecular Chemistry through the European Social Fund for Regional

-p

Development, Competitiveness Operational Programme Axis 1, Project InoMatPol (ID

re

P_36_570, Contract 142/10.10.2016, cod MySMIS: 107464) is gratefully acknowledged.

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Captions

re

Scheme 1. The synthetic procedures towards naphthalene-1,8-dicarboxylic acid derivatives. Fig. 1. Absorption UV-VIS spectra of the naphthalic anhydride derivatives in DMF.

lP

Fig. 2. Absorption UV-VIS spectra of the naphthalimide derivatives in DMF. Fig. 3. Emission spectra of the compounds 1-4.

na

Fig. 4. Emission spectra of the compounds 5-7.

Fig. 5. Fluorescence spectra of derivative 2 in selected solvents.

derivatives.

ur

Fig. 6. Time-resolved decay profile of the naphthalic anhydride and naphthalimide

Jo

Fig. 7. Correlation graphs between the frequencies obtained using Catalan parameters and experimentally frequencies of derivative 3: a) absorption; b) emission; c) Stokes shift. Fig. 8. Linear relationship between the experimental and calculated frequencies using relation (2) for derivative 6: a) absorption; b) emission; c) Stokes shift. Fig. 9. Fluorescence spectra changes of derivative 2 in DMF upon addition of picric acid. Fig. 10. Stern-Volmer plot for quenching of 2 by picric acid. Table 1. Absorption and fluorescence wavenumbers, Stokes shifts (cm-1) and fluorescence quantum yields (%) of some naphthalic anhydride derivatives. Table 2. Absorption, fluorescence wavenumbers, Stokes shifts (cm-1) and fluorescence quantum yields (%) of some naphthalimide derivatives. Table 3. Excited state lifetimes of some naphthalic anhydride and naphthalimide derivatives. Table 4. Some empirical solvatochromic parameters of the solvents. 17

Journal Pre-proof Table 5. Susceptibility constants using the multiple regression analysis of equations (1) and

Jo

ur

na

lP

re

-p

ro

of

(2).

18

Journal Pre-proof Table 1. Absorption and fluorescence wavenumbers, Stokes shifts (cm-1) and fluorescence quantum yields (%) of some naphthalic anhydride derivatives. Compound

1

2

No.

Solvent

υa

υem

Δυ

Φ

υa

υem

Δυ

Φ

υa

1

Dioxane

29586

26205

3381

3.88

24938

19485

5453

56.91

25000

1

2

Toluene

29375

24563

4762

4.52

24814

20198

4606

52.99

24814

2

Ethyl acetate 29586

26288

3298

5.12

24712

19091

5661

29.08

24691

1

3

DCM

29325

25880

3415

7.17

23866

19090

4786

65.23

23981

1

5

DCE

29325

25900

3405

<0.01

23585

19015

4570

30.24

23868

1

6

Methanol

29498 355549

3999

6.96

24155

18505

5650

<0.01

24213

1

7

Acetonitrile

29598

25859

3639

5.92

24086

18336

5758

5.83

24155

1

8

DMF

29412

26219

3193

0.95

24096

18386

5710

16.61

24096

1

9

DMSO

29325

26246

3078

0.27

23866

18501

5710

<0.01

23923

1

-p

ro

of

4

re

DCM - dichloromethane; DCE - dichloroethane; DMF - dimethylformamide; DMSO -

Jo

ur

na

lP

dimethyl sulfoxide.

19

Journal Pre-proof Table 2. Absorption, fluorescence wavenumbers, Stokes shifts (cm-1) and fluorescence quantum yields (%) of some naphthalimide derivatives.

Compound

6

Solvent

υa

υem

Δυ

Φ

υa

υem

Δυ

Φ

1

Dioxane

24631

19316

5315

29.21

24631

19284

5337

65.28

2

Toluene

24450

19612

4838

21.61

24213

19627

4586

45.97

3

Ethyl acetate

24570

18925

5644

7.54

24570

18939

5631

11.19

4

DCM

23697

18864

4833

41.28

23474

18854

4620

74.71

5

DCE

23256

18800

4456

17.13

23364

18776

4588

36.09

6

Methanol

21753

18779

4974

0.35

23809

18681

5128

2.65

7

Acetonitrile

24096

18625

5471

<0.01

23923

18474

5449

4.39

8

DMF

24155

18779

5376

0.20

24213

18734

5479

2.21

9

DMSO

23866

18776

5090

23923

18678

5245

<0.01

ro

of

No

-p

5

Jo

ur

na

lP

re

0.14

20

Journal Pre-proof Table 3. Excited state lifetimes of some naphthalic anhydride and naphthalimide derivatives.

4 8 5

6

7

1.107 0.722

79.94 10.99

94.48 84.47

7.539 5.664

5.52 15.53

92.50 80.69

5.876 6.847

7.50 19.31

11.596 8.953 2.195

46.92 48.67 27.82

50.80 64.08

1.943 7.665

6.31 35.92

81.89 77.88

6.958 7.670

18.11 22.12

46.36

4.571

53.64

53.08 51.33 41.89

ur

3

Jo

2

20.06 84.12

a3

10.00

4.89

10.996

30.29

7.891

42.89

of

0.076 0.027 9.124 9.746 8.083 0.370 0.167 8.899 9.980 8.601 0.446 0.179 1.338 1.508 1.110 0.147 4.979 7.255 5.505 0.248 0.175 4.516 6.854 4.717 0.237 0.172 1.284 0.261

9.84 89.34 89.33

τ3 (ns)

ro

Acetonitrile DMF Toluene DCM DCE Acetonitrile DMF Toluene DCM DCE Acetonitrile DMF Toluene DMF Toluene DMF Toluene DCM DCE Acetonitrile DMF Toluene DCM DCE Acetonitrile DMF Toluene DMF

90.16 10.66 10.67

a2

-p

Dioxane DCM DCE

τ2 (ns) 6.801 1.648 1.442

a1

re

1

τ1 (ns) 1.044 0.446 0.330

lP

Solvent

na

Sample

21

Journal Pre-proof

n

ε

β

α

SA

SB

SP

SdP

Dioxane

1.4224

2.22

0.37

0.00

0.00

0.444

0.737

0.312

Toluene

1.4969

2.38

0.11

0.00

0.00

0.128

0.782

0.284

Ethyl acetate

1.3723

6.08

0.45

0.10

0.00

0.542

0.656

0.603

DCM

1.4242

9.08

0.00

0.3

0.04

0.178

0.761

0.769

DCE

1.4448

10.42

0.0

0.0

0.03

0.126

0.771

0.712

Methanol

1.3288

22.10 0.62

0.93

0.605

0.545

0.608

0.904

Acetonitrile

1.3442

37.50 0.31

0.19

0.044

0.286

0.645

0.974

DMF

1.4305

38.75 0.69

0.10

0.031

0.613

0.759

0.977

DMSO

1.4770

47.24 0.76

0.00

0.830

0.830

1.000

of

Solvent

ro

Table 4. Some empirical solvatochromic parameters of the solvents.

0.012

-p

DCM - dichloromethane; DCE - dichloroethane; DMF - dimethylformamide; DMSO -

Jo

ur

na

lP

re

dimethyl sulfoxide

22

Journal Pre-proof Table 5. Susceptibility constants using the multiple regression analysis of equations (1) and

Eq (2) υa

dSaP

R2

2

26887

-529

1129

-2519

-1652

0.90

3

26602

-366

803

-2015

-1503

0.95

5

26178

-1145

887

-2339

-1004

0.92

6

15971

-1079

1744

-2155

-1148

0.93

2

19244

360

-563

1790

-1925

0.95

3

2028

49

-683

682

-1981

-.97

5

18815

316

76

1203

-1107

0.90

6

18770

287

84

1812

-1248

0.93

2

7643

-888

1692

-4310

-274

0.92

3

6394

415

1485

-2677

458

0.91

5

7677

-1551

1329

-3924

-69

0.90

6

7202

-1367

1660

-3681

100

0.96

Sample

I0

C1

C2

C3

C4

R2

2

27143

-2079

-6745

824

-216

0.92

3

26884

-1876

-5714

581

-162

0.97

5

26826

-422

-10214

7

192

0.92

6

26706

-7709

1182

-691

0.96

18870

-1901

6103

-388

372

0.94

Δυ

ro

of

CSP

-1526

3

19784

-2039

3182

-517

221

0.95

5

18737

-1162

3744

154

263

0.94

6

18690

-1281

4134

124

254

0.95

2

8274

-178

-12818

1212

-588

0.96

3

7087

164

-8896

1099

-383

0.96

5

8086

-502

-11631

10

218

0.92

6

8016

-245

-11643

1058

-944

0.98

2

Jo

υem

bSB

-p

Δυ

aSA

re

υem

Y0

na

υa

Sample

ur

Eq. (1)

lP

(2).

23

Journal Pre-proof

CRediT author statement Alina Nicolescu: Methodology, Investigation; Anton Airinei: Conceptualization, Methodology, Investigation, Writing - Review & Editing; Emilian Georgescu: Conceptualization, Methodology, Investigation, Writing - Review & Editing; Florentina Georgescu: Conceptualization, Writing - Original Draft, Writing - Review &

of

Editing;

ro

Radu Tigoianu: Investigation;

-p

Florin Oancea: Methodology, Resources, Funding acquisition; Calin Deleanu: Conceptualization, Methodology, Investigation, Resources, Writing - Review

Jo

ur

na

lP

re

& Editing, Funding acquisition.

24

Journal Pre-proof

Declaration of interests X The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper (“Synthesis, photophysical properties and solvatochromic analysis of some naphthalene-1,8dicarboxylic acid derivatives”).

of

☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:

Jo

ur

na

lP

re

-p

ro

Alina Nicolescu, Anton Airinei, Emilian Georgescu, Florentina Georgescu, Radu Tigoianu, Florin Oancea, Calin Deleanu

25

Journal Pre-proof



Multinuclear NMR chemical shift assignments



Application of Catalan and Laurence solvatochromic models



Substituent impact on the photophysical properties of naphthalene-1,8-dicarboxylic acid derivatives



The presence of piperidine moiety leads to high fluorescence in solution

Jo

ur

na

lP

re

-p

ro

of



Highlights Novel 1,8-naphthalic anhydride and 1,8-naphthalimide derivatives have been synthesized

26

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10