Tunable Luminescence of Bithiophene-Based Flexible Lewis Pairs

Abstract

Bithiophene-based flexible Lewis pairs with P(O)R2 (R = phenyl, isopropyl) and BMes2 (Mes = 2,4,6-trimethylphenyl) functionalities are able to toggle between closed, Lewis adduct and open, unbound Lewis pair structures. The open structure is favored in strong hydrogen bond donating solvents or at higher temperatures giving rise to an intense charge-transfer (CT) luminescence, while the closed structure without this emission dominates in non-hydrogen bond donating solvents or at lower temperatures. Intermediate solvents result in an equilibrium mixture of both structures, which shows unusual mixed emission that is dependent on excitation wavelength.

4,7‐Bis[3‐(dimesitylboryl)thien‐2‐yl]benzothiadiazole: Solvato‐, Thermo‐, and Mechanochromism Based on the Reversible Formation of an Intramolecular B−N Bond

“…Wang and co‐workers reported another type of boron‐containing compounds that exhibited chromic behavior based on reversible structural changes through the formation/cleavage of intramolecular C−C and C−B bonds upon photoirradiation and heating . An example of a “flexible” Lewis pair, containing intramolecular B−O coordination bonds between boron atoms and phosphine oxides was reported by Wolf and co‐workers . The equilibrium between nonbonded and bonded forms was sensitive to temperature and solvents, and compounds with such flexible Lewis pairs exhibited thermo‐ and solvatochromism.…”

“…Chromic materials, that is, materials that exhibit color changes in response to external stimuli, such as light, temperature changes, redox reactions, solvents, and mechanical forces, have attracted much attention in the context of a variety of applications, including colorimetric chemosensors, memory devices, and light‐control glass . Such chromic phenomena can be induced by structural isomerization; phase transitions in liquid crystals; or changes in the intermolecular interactions, for example, in hydrogen‐bond networks, π‐stacking alignments, metal–metal interactions, molecular aggregation, redox state, or the reversible formation/cleavage of coordination bonds …”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] Such chromic phenomena can be induced by structural isomerization; [2] phase transitions in liquid crystals; [3,4] or changes in the intermolecular interactions, for example, in hydrogen-bond networks, [5,6] p-stacking alignments, [4,7,8] metal-metal interactions, [6,9] molecular aggregation, [8,10] redox state, [11] or the reversible formation/cleavage of coordination bonds. [12][13][14][15][16] Boron-containing p-conjugated molecules are of interest because they can form reversible coordination bonds between the vacant po rbitalo ft he Lewis acidic boron center and the electron pairo fL ewis basic species, which results in significant changes to the electronic structure of the p-conjugated system. [12,17] The group of Ta mao and Yamaguchir eported that trianthrylborane derivativesc ould be used as colorimetric sensors for fluoride ions based on the formation of BÀFc oordina-tion bonds.…”

“…[18] An example of a" flexible" Lewis pair,c ontaining intramolecular BÀOc oordination bonds between boron atoms and phosphine oxidesw as reported by Wolf and co-workers. [16] The equilibrium between nonbonded and bondedf orms was sensitive to temperature and solvents, and compounds with such flexible Lewis pairs exhibited thermo-a nd solvatochromism.…”

Biological Imaging with Medium‐Sensitive Bichromatic Flexible Fluorescent Dyes

“…Our bichromatic fluorescent dye system is based on the shape‐shifting structure shown in Figure . The fluorescent bithiophene core is in equilibrium between the closed and open forms, which respectively give rise to bright‐blue and yellow emission under UV light . The open form is predominant in strong hydrogen‐bond (HB) donating environments such as water, while the closed form is favored in weak HB donors such as lipids.…”