The unquenched triplet excited state of the fluorescent OFF/ON Bodipy-derived molecular probe based on photo-induced electron transfer

Abstract

Fluorescent molecular probes based on photo-induced electron transfer (PET) are well-known for which fluorescence is efficiently tuned OFF/ON by a PET process. Now we demonstrate that the triplet excited state of the probes is unable to be quenched by PET, which is in stark contrast to the singlet excited state (fluorescence). This conclusion was proved by the preparation of a fluorescent molecular probe BDP-DPA, which shows enhanced fluorescence upon addition of a Zn(ii) salt. With fluorescence spectroscopy, nanosecond transient absorption spectroscopy and electrochemical studies, we found that the triplet excited state of BDP-DPA was not quenched by any PET process, although the singlet excited state (fluorescence) of BDP-DPA was quenched. The results are useful for the study of the triplet excited states of organic chromophores and for designing external stimuli-activatable triplet photosensitizers for triplet-triplet annihilation upconversion and photodynamic therapy.

Unexpected Nucleophilic Substitution Reaction of BODIPY: Preparation of the BODIPY–TEMPO Triad Showing Radical‐Enhanced Intersystem Crossing

“…According to previous reports, the preparation of the triad from meso ‐chloro‐BODIPY should be a rather straightforward substitution reaction at the 8‐chloromethyl site (see DBT′, expected structure, Scheme ) . However, after the reaction, the 1 H NMR spectrum of the product indicated that the four methyl groups on the BODIPY chromophore are inequivalent (see Figures S3 and S4 in the Supporting Information for the spectrum).…”

“…However, after the reaction, the 1 H NMR spectrum of the product indicated that the four methyl groups on the BODIPY chromophore are inequivalent (see Figures S3 and S4 in the Supporting Information for the spectrum). Single‐crystal XRD diffraction gave the molecular structure, which is drastically different to the expected “normal” molecular structure . Indeed, following single‐crystal XRD and 1 H NMR analyses, the molecular structure was unambiguously assigned to DBT, not the initially expected DBT′ (Scheme ).…”

“…For instance, an amine moiety can be introduced to construct fluorescent molecular probes, for example, for the selective detection of metal cations,, pH sensing, or as fluorophores , . However, through the preparation of new derivatives by using this “established” substitution reaction, and after careful examination of the 1 H NMR spectral patterns of the new compounds (Scheme ) as well as a comparison with those reported in the literature, we found that the previous assignments of the molecular structures of the products of this kind of substitution reaction on BODIPY were inaccurate . The correct structures were unambiguously established for the present compounds (Scheme ) through single‐crystal XRD molecular structure determination.…”

Tuning the Triplet Excited State of Bis(dipyrrin) Zinc(II) Complexes: Symmetry Breaking Charge Transfer Architecture with Exceptionally Long Lived Triplet State for Upconversion

“…The thermodynamic feasibility of SBCT was also estimated employing the Rehm–Weller analysis, which further confirmed the occurrence of SBCT in bis(dipyrrin) complexes under study (Table 2). [41, 42] …”

“…[30] The thermodynamic feasibility of SBCT was also estimated employing the Rehm-Weller analysis, which further confirmed the occurrence of SBCT in bis(dipyrrin) complexes under study (Table 2). [41,42] Femtosecond/nanosecond transient absorption spectra: symmetry charge transfer and intersystem crossing…”