Conformational Restrictions in meso‐(2‐Thiazolyl)–BODIPYs: Large Stokes Shift and pH‐Dependent Optical Properties

Abstract

Design, synthesis and characterization of a series of thiazole appended BODIPY derivatives 1-4 reported. The fluorescence emission colors of 1-4 were fine-tuned by modulating the dihedral angle between BODIPY and thiazole by judiciously varying the number of methyl substituents on both BODIPY and thiazole moieties. Compounds 1 and 2 with less number of methyl substituents on BODIPY core showed large Stokes shift (~ 110 nm) compared to the derivatives 3 and 4 with more number of methyl substituents. In addition, the optical properties of 1 and 2 are sensitive to pH of the medium. The experimentally observed results were corroborated with theoretical calculations.

A Solution‐Processable meso‐Phenyl‐BODIPY‐Based n‐Channel Semiconductor with Enhanced Fluorescence Emission

“…Therefore, BDY‐4T‐BDY fluorescence seems to originate only from a twisted intramolecular charge transfer (TICT) state. These observations clearly indicate that highly emissive locally excited (LE) state becomes more effective in the new molecule while non‐radiative decay pathways are minimal as a result of increasing D‐A dihedral angle (∼66° for meso ‐phenyl vs. ∼49° for meso ‐thienyl), reducing π‐donor strength (Ph‐2T‐Ph vs. 4T), and restricting intramolecular D‐A rotations (higher rotational barrier for meso ‐phenyl vs. meso ‐thienyl) . However, note that higher polarity medium is still found to facilitate LE‐state→TICT‐state transition in the new molecular structure, and concurrent emissions from both emissive states could be observed in relatively polar solvents (Figures B and 4 C) .…”

“…These observations clearly indicate that highly emissive locally excited (LE) state becomes more effective in the new molecule while non-radiative decay pathways are minimal as a result of increasing D-A dihedral angle (~66°for mesophenyl vs.~49°for meso-thienyl), reducing π-donor strength (Ph-2T-Ph vs. 4T), and restricting intramolecular D-A rotations (higher rotational barrier for meso-phenyl vs. meso-thienyl). [35,36] However, note that higher polarity medium is still found to facilitate LE-state!TICT-state transition in the new molecular structure, and concurrent emissions from both emissive states could be observed in relatively polar solvents ( Figures 4B and 4 C). [34] The fluorescence quantum yield (Φ F ) and lifetime (τ F ) measurements point to improved fluorescence characteristics in the new molecular design, and they align well with the proposed fluorescence mechanisms.…”

“…4T in BDY‐4T‐BDY) and (iii) increasing D‐A dihedral angle/rotational barrier (BODIPY‐Ph vs . BODIPY‐T in BDY‐4T‐BDY) to minimize non‐radiative decays and the formation of twisted intramolecular charge‐transfer (TICT) . The new semiconductor shows a large dihedral angle (∼66°) between BODIPY and meso ‐phenyl units and large local dipoles (μ=3–4 D); both provide good solubility in common organic solvents.…”

“…The molecular design rationales used here are: (i) attaching BODIPY end units to the πdonor unit through meso-positions to facilitate electron-transport, (ii) decreasing π-donor strength (Ph-2T-Ph vs. 4T in BDY-4T-BDY) and (iii) increasing D-A dihedral angle/rotational barrier (BODIPY-Ph vs. BODIPY-T in BDY-4T-BDY) to minimize nonradiative decays and the formation of twisted intramolecular charge-transfer (TICT). [33][34][35][36] The new semiconductor shows a large dihedral angle (~66°) between BODIPY and meso-phenyl units and large local dipoles (μ = 3-4 D); both provide good solubility in common organic solvents. This solution processability enables convenient purification and thin-film fabrication for the new semiconductor.…”

A Strongly Fluorescent Molecular Material Responsive to Physical/Chemical Stimuli and their Coupled Impact

“…[6][7][8][9][10][11][12] pH control of the fluorescencer esponse is of significant interest in terms of chemical sensing applications. [13][14][15][16][17][18] There are severale xamples where temperaturei su sed as a facile stimulus to alter the fluorescencer esponse. [19][20][21][22][23][24] It would be interesting to explore new supramolecular systemst hat show sensitivef luorescence emission variations in response to multiple stimuli, as individual and combination effects.…”