Nature‐Inspired Functional Chromophores from Biomimetic o‐Quinone Chemistry

Abstract

Dedicated to Professor Franco Cozzi on the occasion of his 70th birthday.A concise highlight of the main types of chromophoric systems obtained in the authors' and other laboratories through biomimetic chemistry or synthetic manipulation of natureinspired o-quinones is the primary focus of this Minireview. Following oxidative conversion of a variety of natural catechol substrates like DOPA, dopamine, 5-S-cysteinyldopa and caffeic acid, in the presence of suitable additives, a remarkable variety of chromophoric systems can be produced, which display specific optical and electronic properties, e. g. acidichromism, solvatochromism or strong emission upon excitation. Such properties can be tailored for specific applications through rational synthetic manipulations and/or fine-tuning through non-covalent and supramolecular interactions. Practical access routes to the reported o-quinone-derived chromophoric systems are illustrated along with the main prospective applications.

Synthesis and Electronic Properties of Conjugated syn,syn‐Dithienothiazine Donor‐Acceptor‐Donor Dumbbells

“…[16] The iodinated precursors 2 are formed by monolithiation followed by quenching with molecular iodine at À 78 °C (Scheme 1). [13,14] With iodinated syn,syn-dithienothiazines 2 in hand and bisboronic acids or bisboronates 3 the stage is set for the Suzuki synthesis of syn,syn-dithieno [1,4]thiazine dumbbells 4, which are obtained after workup and purification in moderate to good yield (Scheme 2).…”

“…According to GP1 and after washing of the precipitated crude product with DME and n-hexane and drying in vacuo compound 4 a (107 mg, 66 %) was obtained as a red solid, Mp 197 °C (dec.), R f (n-hexane/ethyl acetate 20 : 1) = 0.36. 1 (11), 686 (32), 685 (41), 684 ([M] + , 100), 654 (13), 652 (17), 618 (13), 342 ([C 17 H 9 FN 3 ], 15), 310 (10), 287 (10), 278 (13), 272 (10), 256 (11), 193 (13). IR ṽ [cm À 1 ]: 3059 (w), 3043 (w), 2916 (w), 2852 (w), 1597 (w), 1568 (m), 1559 (m), 1497 (s), 1435 (m), 1404 (m), 1373 (m), 1339 (w), 1285 (w), 1260 (w), 1211 (s), 1192 (w), 1148 (w), 1103 (w), 1088 (w), 1057 (w), 1028 (w), 999 (m), 947 (w), 935 (w), 837 (m), 808 (s), 775 (m), 762 (m), 737 (w), 710 (s), 644 (w), 617 (w).…”

“…According to GP1 and addition of water and dichloromethane to the reaction mixture, extraction of the aqueous phase with dichloromethane (3 × 20 mL), drying of the combined organic layers (anhydrous magnesium sulfate), evaporation of the solvents, absorption of the crude product on Celite®, chromatography on silica gel (n-hexane/acetone 30 : 1, 0.5 % triethylamine) and trituration of the product with acetone (3 mL) under ultrasonication for 5 min and drying in vacuo compound 4 d (87 mg, 37 %) was obtained as an orange solid, Mp 128-129 °C, R f (nhexane/acetone 30 : 1) = 0.45. 1 H NMR (500 MHz, acetone-d 6 /CS 2 5 : 1): δ 0.90-0.97 (m, 9 H), 1.35-1.47 (m, 18 H), 1.71-1.77 (m, 6 H), 2.73-2.76 (m, 6 H), 6.10 (d, 3 J HH = 5.5 Hz, 3 H), 6.39 (s, 3 H), 7.11 (d, 3 J HH = 5.4 Hz, 3 H), 7.18 (s, 3 H), 7.29-7.39 (m, 15 H). 13 C NMR (125 MHz, acetone-d 6 /CS 2 5 : 1): δ 14.8 (CH 3 ), 23.7 (CH 2 ), 30.1 (CH 2 ), 32.4 (CH 2 ), 32.7 (CH 2 ), 36.5 (CH 2 ), 103.9 (C quat ), 105.4 (C quat ), 117.3 (CH), 120.8 (CH), 121.7 (CH), 124.5 (CH), 129.0 (CH), 131.1 (CH), 135.9 (C quat ), 140.8 (C quat ), 142.0 (C quat ), 143.3 (C quat ), 144.5 (C quat ), 145.3 (C quat ).…”

“…IR ṽ [cm À 1 ]: 3030 (w), 2961 (w), 2916 (w), 2901 (w), 1504 (s), 1472 (m), 1435 (m), 1417 (m), 1381 (w), 1366 (w), 1339 (w), 1285 (w), 1213 (s), 1150 (w), 1138 (w), 1099 (w), 1090 (w), 1061 (w), 1026 (w), 997 (w), 966 (w), 943 (w), 935 (w), 907 (w), 839 (m), 820 (m), 810 (w), 773 (w), 764 (w), 741 (w), 696 (s), 679 (w), 660 (w), 638 (w According to GP2 using 20 mol % bis(dibenzylideneacetone)palladium and 24 mol % tri-tert-butylphosphanetetrafluoroborate as a catalyst system and after trituration of the crude product first with n-hexane under ultrasonication for 15 min and then with hot ethanol and drying in vacuo compound 4 k (161 mg, 68 %) was obtained as a beige solid, Mp 170-174 °C (dec.), R f (n-hexane/ ethyl acetate 20 : 1) = 0.13. 1 H NMR (300 MHz, acetone-d 6 /CS 2 5 : 1): δ 0.92-0.97 (m, 6 H), 1.37-1.46 (m, 12 H), 1.70-1.76 (m, 4 H), 2.71-2.76 (m, 4 H), 6.10 (d, 3 J HH = 5.4 Hz, 2 H), 6.60 (s, 2 H), 7.12 (d, 3 J HH = 5.5 Hz, 2 H), 7.17 (d, 3 J HH = 7.9 Hz, 2 H), 7.32-7.35 (m, 4 H), 7.38-7.41 (m, 4 H), 7.55 (t, 3 J HH = 7.9 Hz, 1 H). 13…”

“…Donor π‐systems, i. e. electron‐rich carbo‐ and heterocycles, are functional chromophores, [1] which play a pivotal role in organic electronics, [2] in particular in the fields of molecule‐based photonics and photovoltaics [3] . As a consequence of their inherently reversible low oxidation potentials, di‐ and tri(hetero) arylamines perfectly fulfill electronic prerequisites as hole conducting molecules [4] .…”