untitled European Journal of Chemistry 5 (3) (2014) 463‐468 European Journal of Chemistry ISSN 2153‐2249 (Print) / ISSN 2153‐2257 (Online)  2014 Eurjchem Publishing ‐ Printed in the USA http://dx.doi.org/10.5155/eurjchem.5.3.463‐468.973 European Journal of Chemistry Journal homepage: www.eurjchem.com Oxonium heterocyclic quinone in the synthesis of some cyanine dyes and their antimicrobial activity Maha Mobaruk Gomaa Chemistry Department, Faculty of Science, Aswan University, Aswan, 81528, Egypt *Corresponding author at: Chemistry Department, Faculty of Science, Aswan University, Aswan, 81528, Egypt. Tel.: +2.097.2305300. Fax: +2.012.2811224. E‐mail address: mahamobarak81@yahoo.com (M.M. Gomaa). ARTICLE INFORMATION ABSTRACT DOI: 10.5155/eurjchem.5.3.463‐468.973 Received: 17 November 2013 Received in revised form: 01 March 2014 Accepted: 10 March 2014 Online: 30 September 2014 KEYWORDS The motivation of the synthetic process of new heterocyclic cyanine dyes is to improve the specific characterization, photosensitization behavior, and probable application in the field of biology, medical science and physics. New heterocyclic compounds having oxonium nuclei were prepared and employed for the synthesis of some new photosensitizers cyanine dyes (monomethine, trimethine and styryl cyanines). The electronic visible absorption spectra of all the synthesized cyanines were investigated in 95% ethanol to attempt and throw some light on the influence of such new heterocyclic nuclei and to compare or evaluate spectral behaviors. Antimicrobial activity of selected compounds against some bacterial strains was tested. Structural identification was carried out via elemental analysis, IR and 1H NMR. Oxonium Synthesis Cyanine dyes Visible spectra Photosensitizers Antimicrobial activity 1. Introduction Cyanine dyes have found various applications in different fields, such as antimicrobial agents [1‐4], photographic sensiti‐ zers, heat developable photosensitizing materials [5‐7], and color photography [8]. Cyanine dyes also used as optical recording materials [9‐15], in manufacturing of blue filter to laminate of an organic electroluminescent element, and color filter showed highly pure light emission [16] and antioxidants [17]. Cyanine dyes are colorant compounds used in staining of internal limiting membrane (ILM) [18] and used as fluorescent dyes in DNA detection [19‐23]. Quinone derivatives are widely used as fungicides [24,25], and antibacterial agent [25‐29]. This paper reports the synthesis and characterization of a series of new monomethine, trimethine and styrylmethine cyanine dyes, and also their structure‐property relationship of these dyes from their visible absorption spectra. 2. Experimental 2.1. Instrumentation All melting points are uncorrected. Elemental analysis was carried out at the Micro Analytical Center (Cairo University). The IR (KBr) spectra were determined with Perkin‐Elmer Infrared 127B Spectrophotometer (Cairo University). 1H NMR spectra were recorded with a Bruker AMX‐250 spectrometer. The electronic absorption spectra were recorded within the wavelength range (350‐700 nm) on 6405 UV‐Visible recording spectrophotometer, Faculty of Science, Aswan, Egypt. Mass spectra were recorded on an HPMs 6988 spectrometer (Cairo University). 2.2. Synthesis of 2‐acetyl‐3‐amino‐1,4‐naphthoquinone (2) This compound was prepared according to references described earlier (Scheme 1) [30,31]. 2.3. Synthesis of N‐(3‐acetyl 1,4‐dioxo‐1,4‐dihydro naphthalen‐2yl)acetamide (3) A pure sample of compound 2 was dissolved in acetic anhydride and the reaction mixture was refluxed for 3‐5 h, filtered, concentrated and cooled. The product 3 was precipitated on dilution with water and crystallized from ethanol (Scheme 1). Color: Red. Yield: 80%. M.p: 258‐260 °C. FT‐IR (KBr, , cm‐1): 3400‐3100 (NH), 1713‐1620 (Acyclic C=O), 1650 (Quinone ring), 1355 (C‐N). 1H NMR (400 MHz, DMSO‐d6, δ, ppm): 7.89‐7.26 (m, 4H, Ar‐H), 6.97 (s, 1H, NH), 2.54 (m, 6H, 2CH3). MS (El, m/z): 257, 59. Anal. calcd. for C14H11NO4: C, 65.36; H, 4.28; N, 5.44. Found: C, 65.36; H, 4.27; N, 5.66%. 464 Gomaa / European Journal of Chemistry 5 (3) (2014) 463‐468 O O CH3CONH2 NaOH O O NH2 O CH3 O O O CH3 N H O CH3 EtOH N O O O CH3 CH3 MeI EtOHN O O O CH3 CH3 CH3 I N I EtOH/Pip EtOH/Pip EtOH/Pip N I N N O O O CH CH3 CH3 I N O O O CH CH3 CH3 I N O O O CH CH3 CH3 I N N NI (1) (2) (3) (4)(5) (6a) (6b) (6c) ClCl Ac2O HCl N O O O CH3 CH3 CH3 I (5) Cl I I I Scheme 1 2.4. Synthesis of 2,4‐dimethyl‐5,10‐dioxo‐5,10‐dihydro naphtho[2,3‐d][1,3]oxazin‐3‐ium chloride (4) A pure sample of compound 3 was dissolved in ethanol (30 mL), and then hydrochloric acid (1 mL) was added. The reaction mixture was refluxed for 2 h; filtered hot, concentrated and cooled. The product 4 was precipitated on dilution with water and crystallized from ethanol (Scheme 1). Color: Brownish red. Yield: 75%. M.p: 217‐ 220 °C. FT‐IR (KBr, , cm‐ 1): 2921 (Chloride salt), 1634 (Quinone ring), 1480 (C=N), 1350 (C‐N), 1150 (C‐O‐C cyclic). 1H NMR (400 MHz, DMSO‐d6, δ, ppm): 8.01‐6.93 (m, 4H, Ar‐H), 1.69 (s, 3H, CH3 at C4), 1.31 (s, 3H, CH3 at C2). MS (El, m/z): 275.5, 132. Anal. calcd. for C14H10NO3Cl: C, 60.98; H, 3.62; N, 5.08. Found: C, 60.99; H, 3.62; N, 5.09%. 2.5. Synthesis of 1,2,4‐trimethyl‐5,10‐dioxo‐5,10‐dihydro naphtho[2,3‐d][1,3]oxazine‐1,3‐diium chloride iodide (5) A pure sample of compound 4 was suspended in excess of ethyl (methyl) iodide and heated in a sealed tube at 140 °C for 3 h. The sealed tube was cooled, opened and the product 5 was collected, washed with ether and crystallized from ethyl alcohol to give brown crystals (Scheme 1). Color: Dark black. Yield: 70% M.p.: 188‐190 °C. FT‐IR (KBr, , cm‐1): 1155 (C‐O‐C cyclic), 1489 (C=N),1633 (C=O, Quinone), 2917 (quaternary salt ), 1360 (C‐N). 1H NMR (400 MHz, DMSO‐d6, δ, ppm): 1.10 (s, 3H, CH3 (Methyl iodide)), 3.53 (s, 6H, 2CH3), 7.43‐8.52 (m, 4H, Ar‐ H). MS (El, m/z): 417.5, 156. Anal. calcd. for C15H13NO3ClI: C, 43.11; H, 3.11; N, 3.35. Found: C, 43.10; H, 3.12; N, 3.35%. 2.6. Synthesis of compound 6a‐c dyes An ethanolic solution of equimolar amount of compound 5 and 1‐ethyl‐[pyridinium, quinolinium and/or iso‐quinolinium] salts (0.01 mol) were refluxed for 7‐8 h, in the presence of piperidine (3‐5 drops), filtered hot, concentrated and acidified with acetic acid. The precipitated products after dilution with water filtered off and crystallized from ethanol to give the corresponding products (Scheme 1 and 2). 4‐((1‐Ethylpyridin‐1‐ium‐4‐yl)methylene)‐1,2‐dimethyl‐5,10‐ dioxo‐5,10‐dihydro‐4H‐naphtho(2,3‐d)(1,3)oxazin‐1‐ium iodide (6a): Color: Red. Yield: 70%. M.p: 223‐225 °C. MS (El, m/z): 614, 77. Anal. calcd. for C22H20N2O3I2: C, 43.02; H, 3.28; N, 4.56. Found: C, 42.93; H, 3.20; N, 4.43%. Gomaa / European Journal of Chemistry 5 (3) (2014) 463‐468 465 Scheme 2 4‐((1‐Ethylquinolin‐1‐ium‐4‐yl)methylene)‐1,2‐dimethyl‐5,10 ‐dioxo‐5,10‐dihydro‐4H‐naphtho(2,3‐d)(1,3)oxazin‐1‐ium iodide (6b): Color: Deep red. Yield: 75%. M.p: 203‐205 °C. FT‐IR (KBr, , cm‐1): 1650 (Quinone ring), 1487 (C=N), 1360 (C‐N), 2800 (N‐C2H5 of heterocyclic group), 2950 (quaternary salt). 1H NMR (400 MHz, DMSO‐d6, δ, ppm): 1.02 (s, 3H, CH3 (methyl iodide)), 1.13 (t, J = 6.9 Hz, 3H, CH3), 3.10 (q, 2H, CH2), 3.52 (s, 3H, CH3), 6.50‐8.83 (m, 11H, 10Ar‐H+=CH). MS (El, m/z): 664, 156. Anal. calcd. for C26H22N2O3I2: C, 47.01; H, 3.34; N,4.22. Found: C, 46.90; H, 3.39; N, 4.27%. 4‐((2‐Ethylisoquinolin‐2‐ium‐1‐yl)methylene)‐1,2‐dimethyl‐ 5,10‐dioxo‐5,10‐dihydro‐4H‐naphtho(2,3‐d) (1,3)oxazin‐1‐ium‐ iodide (6c): Color: Deep red. Yield: 85%. M.p: 177‐ 180 °C. MS (El, m/z): 664, 297. Anal. calcd. for C26H22N2O3I2: C, 47.01; H, 3.34; N, 4.22. Found: C, 46.95; H, 3.30; N, 4.23%. 2.7. Synthesis of 4‐(2,2‐diethoxyethyl)‐1,2‐dimethyl‐5,10‐ dioxo‐5,10‐dihydronaphtho(2,3‐d)(1,3)oxazine‐1,3‐diium chloride iodide (7) A mixture of the quaternary compound 5 (0.01 mol) and (0.01 mol) of triethyl‐ortho‐formate was dissolved in ethanol (50 mL) containing piperidine (3‐5 drops) and refluxed for 4 h, filtered hot to remove unreacted materials, concentrated to one half its initial volume, cooled, acidified with acetic acid, and precipitated by cold water, filtered off and crystallized from ethanol to give the corresponding product 7 (Scheme 3). Color: Brown. Yield: 68%. M.p: 193‐195 °C. FT‐IR (KBr, , cm‐1): 1155‐ 1018 (C‐O‐C cyclic), 1227 (C‐O ether), 1490 (C=N), 1634 (C=O Quinone), 2919 (quaternary salt). 1H NMR (400 MHz, DMSO‐d6, δ, ppm): 1.22 (s, 3H, CH3 (Methyl iodide)), 3.54 (s, 3H, CH3), 1.25 (t, J = 6.5 Hz, 6H, 2CH3 of diethoxy ethyl), 3.85 (q, 4H, 2CH2 diethoxy ethyl), 4.65 (t, J = 6.9 Hz, 1H, CH of diethoxy ethyl), 3.65 (d, J = 6.7 Hz, 2H, CH2 of diethoxy ethyl), 7.15 ‐ 8.53 (m, 4H, Ar‐H). MS (El, m/z): 519.5, 156. Anal. calcd. for C20H23NO5ClI: C, 46.22; H, 4.46; N, 2.69. Found: C, 46.00; H, 4.40; N, 2.54%. 2.8. Synthesis of compound 8a‐c dyes Equimolar amounts of compound 7 and 2‐methyl quaternary salts (α(γ)‐picoline and\or quinaldine) ethyl iodide (0.01 mol) were dissolved in ethanol (30 mL) then piperidine (3‐5 drops) was added. The reaction mixture was refluxed for 8 h, filtered hot, concentrated, cooled and acidified with acetic acid. The precipitated products (8a‐c) after dilution with water were collected and crystallized from aqueous ethanol (Scheme 3). 4‐((Z)‐3‐(1‐Ethylpyridin‐1‐ium‐2‐yl)allylidene)‐1,2‐dimethyl‐ 5,10‐dioxo‐5,10‐dihydro‐4H‐naphtho [2,3‐d] [1,3] oxazin‐1‐ium iodide (8a): Color: Red. Yield: 65%. M.p: 208‐210 °C. MS (El, m/z):640, 170. Anal. calcd. for C24H22N2O3I2: C, 45.02; H, 3.46; N, 4.38. Found: C, 45.20; H, 3.45; N, 4.33%. 4‐((Z)‐3‐(1‐ethylquinolin‐1‐ium‐2‐yl)allylidene)‐1,2‐dimet‐ hyl‐5,10‐dioxo‐5,10‐dihydro‐4H‐naphtho[2,3‐d][1,3]oxazin‐1‐ium iodide (8b): Color: Violet. Yield: 70%. M.p: ˃300 °C. FT‐IR (KBr, , cm‐1): 1151‐1052 (C‐O‐C cyclic), 1359 (C‐N), 1488 (C=N), 1595 (C=C), 1632 (C= O Quinone), 2917 (quaternary salt). 1H NMR (400 MHz, DMSO‐d6, δ, ppm): 1.30 (s, 3H, CH3 (Methyl iodide)), 3.33 (s, 3H, CH3), 0.88 (t, J = 7.1 Hz, 3H, CH3), 4.25 (q, 2H, CH2), 6.54‐8.90 (m, 13H, 10Ar‐H + ‐CH=). MS (El, m/z):690, 369. Anal. calcd. for C28H24N2O3I2: C, 48.72; H, 3.50; N, 4.06. Found: C, 48.60; H, 3.42; N, 4.09%. 466 Gomaa / European Journal of Chemistry 5 (3) (2014) 463‐468 Scheme 3 4‐((Z)‐3‐(1‐ethylpyridin‐1‐ium‐4‐yl)allylidene)‐1,2‐dimethyl‐ 5,10‐dioxo‐5,10‐dihydro‐4H‐naphtho [2,3‐d] [1,3] oxazin‐1‐ium iodide (8c): Color: Red. Yield: 75%. M.p: 128‐130 °C. MS (El, m/z):640, 297. Anal. calcd. for C24H22N2O3I2: C, 45.02; H, 3.46; N, 4.38. Found: C, 45.11; H, 3.45; N, 4.40%. 2.9. Synthesis of compound 9a‐c dyes An equimolar amounts of heterocyclic quaternary salt (5, 0.01 mol) and aromatic aldehydes (benzaldehyde, p‐nitro benzaldehyde and/or N‐dimethyl benzaldehyde (0.01 mol) were dissolved in absolute ethanol (30 mL), then piperidine (1 mL) was added. The reaction mixture was refluxed for 8‐10 h, filtered hot, concentrated, acidified with acetic and then diluted with water. The precipitated styrylcyanines (9a‐c) were filtered, washed several times with cooled water and then crystallized from the appropriate solvent (Scheme 3). 1,2‐Dimethyl‐5,10‐dioxo‐4‐styryl‐5,10‐dihydronaphtho[2,3‐ d][1,3]oxazine‐1,3‐diium chloride iodide (9a): Color: Red. Yield: 70%. M.p.: 218‐220 °C. MS (El, m/z): 505.5, 156. Anal. calcd. for C22H17NO3ClI: C, 52.25; H, 3.39; N, 2.77. Found: C, 52.40; H, 3.39; N, 2.73%. 1,2‐Dimethyl‐4‐(4‐nitrostyryl)‐5,10‐dioxo‐5,10‐dihydro naphtho(2,3‐d)(1,3)oxazine‐1,3‐diium chloride iodide (9b): Color: Pale red. Yield: 82%. M.p.: ˃300 °C. FT‐IR (KBr, , cm‐1): 1160‐1030 (C‐O‐C cyclic), 1350 (C‐N), 1484 (C=N),1595 (C=C), 1650 (C=O Quinone), 2957 (quaternary salt). 1H NMR (400 MHz, DMSO‐d6, δ, ppm): 1.19 (s, 3H, CH3 (Methyl iodide)), 3.35 (s, 3H, CH3), 8.20‐7.21 (m, 8H, Ar‐H), 5.04‐4.05 (m, 2H, HC=CH). MS (El, m/z): 550.5, 369. Anal. calcd. for C22H16N2O5ClI: C, 47.98; H, 2.93; N, 5.09. Found: C, 47.89; H, 2.88; N, 5.20%. 4‐(4‐(Dimethylamino)styryl)‐1,2‐dimethyl‐5,10‐dioxo‐5,10‐ dihydronaphtho[2,3‐d][1,3]oxazine‐1,3‐diium chloride iodide (9c): Color: Brownish red. Yield: 63%. M.p: 177‐180 °C. MS (El, m/z): 548.5, 504. Anal. calcd. for C24H22N2O3ClI: C, 52.52; H, 4.04; N, 5.10. Found: C, 52.70; H, 4.15; N, 5.22%. 2.10. Antimicrobial studies The tested compounds (3, 4, 5, 6a, 6b, 6c, 8a, 8b, 9a and 9b) were dissolved in DMSO to give a final concentration (1 mg/mL). Susceptible sterile discs were impregnated by the tested substance (50 µg/disc) via a means of micropipette. The biological activity for each substance was tested on surface‐ seeded nutrient agar medium with the prepared susceptible discs. Bacterial strains and the biological effect are shown in Table 1. 3. Results and discussion 3.1. Synthesis Reaction of equimolar ratio of 1,2,4‐trimethyl‐5,10‐dioxo‐ 5,10‐dihydronaphtho [2,3‐d] [1,3] oxazine‐1,3‐diium chloride iodide (5) with heterocyclic quaternary salts of pyridinium, quinolinium and isoquinolinium ethyl iodide in the presence of piperidine as basic catalysis afforded the desired compound 6a‐c dyes (Scheme 1). Gomaa / European Journal of Chemistry 5 (3) (2014) 463‐468 467 Table 1. Biological activity of some newly synthesized compounds. Compound Mean diameter inhibition zone (mm) Bacillus subtillus Escherichia coli Staphylococcus aureus Pseudomonas aeruginosa Candida albicans Aspergillus niger 3 16 17 17 18 19 17 4 ‐ 11 ‐ 14 15 15 5 20.5 20 15 16 19.5 12 6a 19 15 17 17 22.5 14.5 6b 21.5 21 20 19.5 22 15 6c 20 17 22 15.7 18.5 15.5 8a 15 11 16 ‐ 12 18 8b 19 17 21 14 15 ‐ 9a 20 19 18 16.5 15 15 9b 18 18 16 17 17 19 Standard * 31.5 30 32 37.5 25 23 * Standard which is Miphinicol at conc. 1 mg/mL for Gram positive bacteria, while Keflex was used as standard for Gram negative bacteria at concentration 1 mg/mL. Flucorai was used as standard for fungi at concentration 1 mg/mL. Amikacin was tested as standard at concentration 1 mg/mL for Canadida albicans. Table 2. The electronic absorption spectra of new synthesized cyanine dyes (6a‐c), (8a‐c) and (9a‐c) in 95% EtOH. Monomethine cyanine dyes (6a‐c) 6a 6b 6c max, nm 450 465 460 εmax, mol‐1.cm‐1 1871 1727 2250 Trimethine cyanine dyes (8a‐c) 8a 8b 8c max, nm 460 605, 565, 520 465 εmax, mol‐1.cm‐1 1200 1100, 1650, 1200 1440 Styryl cyanine dyes (9a‐c) 9a 9b 9c max, nm 445 405 460 εmax, mol‐1.cm‐1 1377 1770 1990 Treating on the latter compound 6a‐c by conc. H2SO4 resulted in liberating iodine vapor on warming. This is due to that the above reaction between the compound 5 and heterocyclic quaternary salts of pyridinium, quinolinium and/or isoquinolinium ethyl iodide was suggested to proceed through liberation of hydrogen chloride (dehydrohalogenation) and hydrogen molecule. Additionally, interaction of equimolar ratios of compound 5 with triethyorthoformate in ethanol containing few drops of piperidine as a basic catalysis achieved the corresponding intermediate compound 7 (Scheme 3). Further, reaction of intermediate compound 7 with active methyl heterocyclic quaternary salts (α(γ)‐picoline and /or quinaldine) ethyl iodide gave the corresponding compound 8a‐ c dyes (Scheme 3). Treatment on the latter compound 8a‐c by conc. H2SO4 resulted in liberating iodine vapor on warming. This is due to that the above reaction between the compound 7 and heterocyclic quaternary salts of (α(γ)‐picoline and /or quinaldine) ethyl iodide was suggested to proceed through elimination two molecules of ethanol and liberation of hydrogen chloride molecule. Condensation reaction of equimolar ratios of compound 5 and benzaldehyde, p‐nitrobenzaldehyde and/or N‐dimethyl benzaldehyde between the active methyl group of the former compound and formyl group of the latter ones in the presence of piperidine as basic catalyst and ethyl alcohol as solvent gave the corresponding compound 9a‐c dyes (Scheme 3). The newly synthesized cyanine dyes (6a‐c), (8a‐c) and (9a‐ c) are highly colored compounds, easily soluble in polar organic solvents given green fluorescence but sparingly soluble in non‐ polar solvents and soluble in conc. H2SO4 liberating iodine vapor on warming. 3.2. Spectral behavior The electronic absorption spectrum features (λmax and εmax values) of the newly synthesized cyanine dyes (6a‐c), (8a‐c) and (9a‐c) in ethanol solution are depicted in Table 2. The visible absorption spectra of compound 6a‐c dyes in 95% ethanol undergo bathochromic or hypsochromic shifts depending on the nature of the quaternary salts residue and their linkage position. Thus, the electronic absorption spectra of compound 6a which incorporating a heterocyclic of N‐ethyl pyridin‐4‐ium, showed λmax at 450 nm. Substitution of a heterocyclic of N‐ethyl pyridin‐4‐ium in compound 6a by a heterocyclic of N‐ethylquinolin‐4‐ium in compound 6b resulted in a bathochromic shift of λmax = 15 nm, so compound 6b, exhibited λmax = 465 nm. This is due to the more extensive π‐ delocalization and extra conjugation within the extra phenyl ring in quinolinium ring in compound 6b [32,33]. Additionally, changing the linkage position from 4‐ium in compound 6b which incorporating a heterocyclic N‐ethyl quinolin ‐4‐ium to 1‐ium in compound 6c which incorporating a heterocyclic of N‐ethyl isoquinolin‐1‐ium causes a hypso‐ chromic shift of λmax = 5 nm, so compound 6c showed λmax = 460 nm. This is due to the more extensive π‐delocaliza‐ tion within 4‐ium rather than 1‐ium linkage position (Table 2). The visible absorption spectra of compound 8a‐c dyes in 95% ethanol showed absorption band undergo batho(hypso) chromically shifted depending upon the heterocyclic quaternary residue, and their linkage position. Thus, the absorption spectra of compound 8a quaternary heterocyclic residue of 1‐ethyl pyridin‐2‐ium ethyl iodide showed λmax = 460 nm. Substituting of heterocyclic quaternary residue 1‐ethyl pyridin‐2‐ium ethyl iodide in compound 8a by quaternary heterocyclic residue of 1‐ethyl quinolin‐2‐ium ethyl iodide in compound 8b resulted in strong bathochromic shift of λmax = 60 nm concomitant with the increasing number of absorption bands, 8b λmax = 520, 565, and 605 nm. This is due to the more extensive π‐delocalization within the extra phenyl ring in compound 8b. Additionally, changing the linkage position from 2‐ium linkage position in compound 8a, quaternary heterocyclic residue of 1‐ethyl pyridin‐2‐ium ethyl iodide to 4‐ium in compound 8c, quaternary heterocyclic residue of 1‐ethyl pyridin‐4‐ium ethyl iodide resulted in a remarkable bathochromic shift of λmax = 5 nm, if compared with compound 8a, (8c, λmax= 465 nm). This is due to the increasing of the extension conjugation of 4‐linkage pyridine moiety better than 2‐linkage analogous (Table 2). Finally, the visible absorption spectra of compound 9a‐c dyes in 95% ethanol showed absorption bands influenced by aryl substituents [34]. Thus, styryl cyanine dye 9a show single absorption band located at λmax = 445 nm. Substituting benzaldehyde in dye 9a by p‐nitro benzaldehyde in dye 9b resulted in a hypsochromic shift of λmax = 40 nm (9b, λmax = 405 468 Gomaa / European Journal of Chemistry 5 (3) (2014) 463‐468 nm). This is due to the strong electron withdrawing effect of p‐ NO2 group. Also, substituting p‐nitro‐benzaldehyde in dye 9b by N‐dimethyl benzaldehyde in dye 9c causes a bathochromic shift of λmax = 55 nm, (9c, λmax = 460 nm). This is due to the electron donating effect of two methyl groups (Table 2). 3.3. Antimicrobial activity Structure‐antimicrobial activity relation‐ship for some selected newly synthesized quinone compounds 3, 4, 5, 6a‐c, 8a, 8b, 9a and 9b were studied and determined against some bacterial and fungi strains (Table 1). The data obtained are expressed as size (mm) of inhibition zone. Diameter of the inhibition zones were high (22‐18 mm), moderate (17‐12 mm), slight (11‐1 mm), no response (‐). The final conclusion from this work is that these novel compounds showed significant antibacterial activity according to the following factors: (i) Increasing and/or decreasing conjugation in the dye molecule; (ii) Increasing and/or decreasing the number of the methine group; (iii) The presence of either electron donating and/or accepting group. 4. Conclusion New unsymmetrical cyanine dyes have been prepared incorporating heterocyclic quinone and were identified by chemical and spectroscopic evidences (Elemental analysis, UV‐ Vis, IR, 1H NMR and MS spectra). 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