Crystallographic, Photophysical, NMR Spectroscopic and Reactivity Manifestations of the “8-Heteroaryl Effect” in 4,4-Difluoro-8-(C₄H₃X)-4-bora-3a,4a-diaza-s-indacene (X = O, S, Se) (BODIPY) Systems

Abstract

We have synthesized and fully characterized three novel, yet closely related, heterocyclically meso-substituted (BODIPY) fluorophores 4,4-difluoro-8-(C(4)H(3)X)-4-bora-3a,4a-diaza-s-indacene (X = O, 2-/3-furyl (7/10); Se, 2-selenenyl (9)) through the use of 2-D NMR (COSY, HSQC, and HMBC), single crystal X-ray diffraction, mass spectrometry, elemental analysis, UV-vis spectroscopy, and fluorescent decay lifetimes, for comparison to the previously reported thienyl species (X = S, 2-/3-thienyl (8/11)). Specifically, 7-11 differ formally by chalcogen (O, S, or Se) or chalcogen placement. Solid state comparisons reveal major effects stemming from subtle structural differences which allows for insights into fluorescent crystal engineering. For the 2-heteroatom substitution, an increase in molecular weight (7 < 8 < 9) correlates with an increasing unit cell-volume, a greater orthogonality for the C(4)H(3)X group, and a lower value for Phi(F). Solution and density functional theory (DFT) results reveal interesting platforms for potential in fluorescent studies for neurology. 2-Heterocyclic species show larger lambda(abs,max/em,max) values relative to 3-heterocyclic ones, based on electron withdrawing effects. 10 has the greatest Phi(F) value herein (0.25, toluene). Fluorescence lifetimes were found to be 2.60 (7), 0.74 (8), 0.27 (9), 4.26 (10), and 1.86 ns (11); lambda(em,max) decay was studied for 8. Heterocyclic differences give rise to somewhat different pyrrolic NMR spectroscopic shifts as well. These compounds resist decomposition as seen from titrations with H(2)O(2), and uniformly undergo lambda(abs,max) red-shifting and lowered Phi(F) values as they become brominated with Br(2).

Synthesis and studies of covalently linked meso-furyl boron-dipyrromethene-ferrocene conjugates

“…In particular, for the compound 1, the meso-2-furyl ring retains much of orbital coefficient as compared to phenyl ring of compound IV. This is in total contrast to the orbital coefficient pattern of simple meso-2-furyl BODIPY [25] and meso-4-phenyl BODIPY [28] derivatives where the orbital coefficients are majorly located in BODIPY core.…”

“…The structures of the Compounds 1 and IV (Chart 1) were generated in silico by attaching ferrocene moiety to meso-phenyl [28] and meso-2-furyl [25] BODIPY moieties. The structures were energy optimized using quantum mechanics with density functional theory (DFT) [31] and B3LYP [32] gradient corrected correlation functional method in conjugation with ccdzpv**þ basis set [33] and parameters.…”

“…However, the compound IV is failed to act as redox fluorescent switch because of phenyl spacer which prevented better communication between ferrocene and BODIPY units. Recently, it is showed that the electronic properties of meso-furyl BODIPYs are significantly altered compared to meso-phenyl BODIPYs which is attributed to more inplane orientation of meso-furyl group with BODIPY core [25]. Thus, we thought that if we use furyl group as spacer instead of phenyl group, the communication between BODIPY and ferrocene would be better and such conjugates can act as redox fluorescent switches.…”

Rationalizing the photophysical properties of BODIPY laser dyes via aromaticity and electron-donor-based structural perturbations

“…Changing the substituent at the 8-position offers another useful method for modifying the absorption and fluorescence properties of BODIPYs. An example of this is the work of Kim et al, detailing the changes in these characteristics observed upon altering the atomic number and position of the chalcogen atom of a heterocyclic substituent [24].…”

Theoretical Study of Terminal Vanadium(V) Chalcogenido Complexes Bearing Chlorido and Methoxido Ligands

“…The study of complexes with terminal metal-oxo, sulfido, seleno, and related ligands is an interesting area of inorganic chemistry. This is partly because they are used as reagents and precatalysts [2,3] for organic synthesis and also as models for the active sites in heterogeneous processes. A search in the Cambridge Structural Database (version 5.38, November 2016, plus one update) reveals that the occurrence of terminal chalcogenido complexes diminishes rapidly in the sequence O ≫ S > Se > Te making the oxo complexes the most prevalent.…”