Integration of Cyanine, Merocyanine and Styryl Dye Motifs with Synthetic Bacteriochlorins

Abstract

Understanding the effects of substituents on spectral properties is essential for the rational design of tailored bacteriochlorins for light-harvesting and other applications. Toward this goal, three new bacteriochlorins containing previously unexplored conjugating substituents have been prepared and characterized. The conjugating substituents include two positively charged species, 2-(N-ethyl 2-quinolinium)vinyl- (B-1) and 2-(N-ethyl 4-pyridinium)vinyl- (B-2), and a neutral group, acroleinyl- (B-3); the charged species resemble cyanine (or styryl) dye motifs whereas the neutral unit resembles a merocyanine dye motif. The three bacteriochlorins are examined by static and time-resolved absorption and emission spectroscopy and density functional theoretical calculations. B-1 and B-2 have Qy absorption bathochromically shifted well into the NIR region (822 and 852 nm), farther than B-3 (793 nm) and other 3,13-disubstituted bacteriochlorins studied previously. B-1 and B-2 have broad Qy absorption and fluorescence features with large peak separation (Stokes shift), low fluorescence yields, and shortened S1 (Qy ) excited-state lifetimes (~700 ps and ~100 ps). More typical spectra and S1 lifetime (~2.3 ns) are found for B-3. The combined photophysical and molecular-orbital characteristics suggest the altered spectra and enhanced nonradiative S1 decay of B-1 and B-2 derive from excited-state configurations in which electron density is shifted between the macrocycle and the substituents.

Bacteriochlorin‐bis(spermine) conjugate affords an effective photodynamic action to eradicate microorganisms

“…A small Stokes shift for BCS indicated that the spectroscopic energies are similar to the relaxed energies of the lowest singlet excited state S 1 . This is in accordance with the planar and rigid structure of the tetrapyrolic macrocycle . Therefore, only a minor geometric relaxation takes place in the first excited state.…”

“…Each bacteriochlorin in the set contains a common scaffold and was derived by Suzuki coupling with BC‐Br 3,13 . In 2016, Yang et al synthesized two bacteriochlorins ( BC‐3 and BC‐4 ) bearing cationic groups at the 3‐ and 13‐positions of the macrocycle. The substituents of BC‐3 and BC‐4 have characteristics in common with cyanine dyes, which have terminal N ‐alkylated heterocycles at the ends of a polyene chain.…”

“…In this regard, a promising family of molecules for PDI is provided by bacteriochlorins, tetrahydroporphyrins containing alternating pyrrole and pyrroline rings . Bacteriochlorins differ from other tetrapyrrole macrocycle derivatives because they have an intense long‐wavelength absorption band ( ε ~10 5 M −1 cm −1 ), which is located in the near‐infrared (NIR) region . The characteristics of bacteriochlorins often meet the demands of valuable phototherapeutic agents.…”

Synthesis and photophysical characteristics of 2,3,12,13-tetraalkylbacteriochlorins

“…Two others (BC-MEs and BC-EEs) have alkyl (methyl or ethyl) groups at the 2,12-positions and carboethoxy groups attached directly to the 3,13-positions of the macrocycle. 44,45 The absorption spectrum of each bacteriochlorin consists of four major bands: B y , B x in the near ultraviolet, Q x in the greenyellow and Q y in the NIR region. (A) Absorption and fluorescence spectra.…”

Expanding π-Conjugation in Chlorins Using Ethenyl Linker

“…Enlarging the π-conjugated system in tetrapyrrolic macrocycles leads to significant alteration of their electronic, optical, and electrochemical properties. − Expansion of the conjugated systems can be achieved in several ways, which include attachment of conjugated substituents on the periphery of the macrocycle − or assembling the macrocycle into strongly conjugated arrays, i.e., arrays where the linker allows for significant electronic communication between macrocycles. ,,− Both approaches lead to derivatives with interesting properties, such as panchromatic absorbance, , high quantum yield of near-IR fluorescence, improved two-photon cross-section, high excited state absorptivity, and large hyperpolarizability . Accordingly, resulting derivatives found applications, for example, as near-IR fluorophores, fluorescent probes, , two-photon excitable singlet oxygen photosensitizers, , models for natural light-harvesting antenna, and photosensitizers for dye-sensitized solar cells. , The extent to which extended conjugation affects the properties of tetrapyrrolic macrocycles depends on the strength of electronic interaction between substituents and macrocycles or between individual macrocycles in dyads.…”