A Molecular Rotor Based on an Unhindered Boron Dipyrromethene (Bodipy) Dye

Alamiry, Mohammed A. H.; Benniston, Andrew C.; Copley, Graeme; Elliott, Kristopher J.; Harriman, Anthony; Stewart, Beverly; Zhi, Yong‐Gang

doi:10.1021/cm800702c

Cited by 102 publications

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“…We now report on internal conversion in two boron dipyrromethene dyes for which the meso-phenyl ring is either constrained (Bodipy) or free to rotate (Robod), the latter class of dye being popular rheology probes. [14] Our particular interest lies with understanding the effect of nuclear motion on the ultrafast dynamics of upper-lying excited states. Earlier work has concluded that deactivation of the higher-lying (i.e., S 3 and/or S 2 ) excited states and the simultaneous population of the S 1 states of such dyes occur on timescales of a few hundreds of femtoseconds while vibrational cooling of the S 1 state occurs over approximately 20 ps.…”

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“…This structural change has an important effect on the photophysical properties of the S 1 state in that rotation of the phenylene ring distorts the dipyrrin backbone and thereby promotes nonradiative decay of the excited state; this being the origin of the rotor effect. [14] The absorption (n MAX ) and fluorescence (n FLU ) maxima recorded in toluene solution are given in Table 1, together with the measured fluorescence quantum yields (F F ) and excited-singlet-state lifetimes (t S ). Also given are the molar absorption coefficients measured at the peak maximum.…”

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“…The upward curvature of the PES presents a barrier for such one-dimensional diffusion. To account for the rotor effect observed with Robod, but not Bodipy, it has been proposed [14] that the S 1 PES for Robod contains areas which are close in energy to the S 0 PES, denoted as local pinhole sinks, that are strongly coupled to the S 0 surface, [19] enabling fast nonradiative relaxation. These pinholes, which funnel the excited-state population down to the ground state, are situated on the PES in such a way that frictional forces with surrounding solvent molecules affect the frequency with which they are accessed.…”

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Conformational Effects on the Dynamics of Internal Conversion in Boron Dipyrromethene Dyes in Solution

et al. 2011

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Electronic energy transfer plays a crucial role in many natural processes, ranging from self-protection [1] to repair mechanisms [2] and energy transduction. [3] One of the primary reasons for employing such indirect excitation is that ideal reagents for inducing chemical change, such as electron transfer or conformational exchange, rarely possess optimal light-absorbing properties.[4] This simple strategy of equipping an elaborate photochemical device with an ancillary photon collector, programmed to absorb over a broad spectral range and to emit at a discrete wavelength, is also relevant to artificial photosynthetic systems. Indeed, such strategies may have relevance to the design of dye-sensitized solar cells [5] and certain organic light-emitting diodes.[6] Similar processes also appear relevant to conducting polymers [7] and solar concentrators.[8] A further, and possibly important, role for lightharvesting units is to promote the harmless dissipation of ultraviolet (UV) photons, arising from increased UVB radiation at the Earths surface because of stratospheric ozone depletion that would otherwise initiate photo-degradation. The latter realization has led to the recent investigation of cases where an upper-lying excited state (e.g., S 2 ) of a strongly fluorescent dye functions as the energy acceptor for high-energy photons while the lowest-energy excited state acts as sensitiser for the photonic device.[9] Complementary reports have shown that the S 2 states of certain dyes, notably carotenes [10] and metallo-porphyrins, [11] can be used as energy donors.In terms of protective mechanisms and device efficacy, it is essential that the S 2 state formed through energy transfer undergoes rapid electronic relaxation (i.e., internal conversion) to the corresponding S 1 state, without opening new routes for deleterious or antagonistic chemical steps. Although the S 2 states of most organic molecules tend to be very short-lived, there are notable exceptions [12] and few rules other than the generic Englman-Jortner energy-gap law [13] by which to predict their lifetimes. Even less is understood about how the internal conversion dynamics depend on the molecular structure and the local environment. We now report on internal conversion in two boron dipyrromethene dyes for which the meso-phenyl ring is either constrained (Bodipy) or free to rotate (Robod), the latter class of dye being popular rheology probes. [14] Our particular interest lies with understanding the effect of nuclear motion on the ultrafast dynamics of upper-lying excited states. Earlier work has concluded that deactivation of the higher-lying (i.e., S 3 and/or S 2 ) excited states and the simultaneous population of the S 1 states of such dyes occur on timescales of a few hundreds of femtoseconds while vibrational cooling of the S 1 state occurs over approximately 20 ps. [15] The two dyes, Robod and Bodipy (Scheme 1), differ by virtue of the substitution pattern at the pyrrole units. This structural change has an important effect on the photophysical p...

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Conformational Effects on the Dynamics of Internal Conversion in Boron Dipyrromethene Dyes in Solution

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“…2,3 Recent examples of the applications of BODIPY include biological tags with visible/near IR emission, 4,5 mechanical rotors, 6 lasing, 7-9 dye sensitized solar cells, 10 electroluminescence (EL), 11 and electrogenerated chemiluminescence (ECL). …”

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New Redox Stable Low Band Gap Conjugated Polymer Based on an EDOT−BODIPY−EDOT Repeat Unit

et al. 2009

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The compound 4,4-difluoro-4-borata-3a-azonia-4a-aza-sindacene, more commonly known as BODIPY, has enjoyed a high and rapidly escalating level of interest over the past decade.1 This dye-type material, which can be likened to a porphyrin subunit, has been studied mainly in applications related to its strong absorption and fluorescence properties. 2,3 Recent examples of the applications of BODIPY include biological tags with visible/near IR emission, 4,5 mechanical rotors, 6 lasing, 7-9 dye sensitized solar cells, 10 electroluminescence (EL), 11 and electrogenerated chemiluminescence (ECL). 12The incorporation of the BODIPY unit into conjugated polymers (CPs) is a fascinating prospect. In particular, the strong absorption/emission and tunable color characteristics 13 of BODIPY derivatives mark them as ideal components in copolymers for electrochromic, optoelectronic, and organic solar cell devices. To the best of our knowledge, BODIPY has not been studied as a main chain component in conjugated macromolecular structures, although an organoboronpolymer 14 andaBODIPY-quaterthiophene-BODIPY triad have been reported 15 and a series of BODIPY dyes have been used in blends with CPs for organic solar cell devices. 16In addition to their electronic properties, BODIPY derivatives also exhibit variable redox chemistry, and they have been used as electron donors 17 and acceptors. 18 In the latter case, BODIPY comonomers have the potential of lowering the band gap of CPs (and stabilizing their reduced states), since donor and acceptor units within conjugated structures are able to bring the HOMO/LUMO energy levels closer together. For organic solar cell applications low band gap CPs are highly desirable, but the stability of doped states is often poor in such materials. A recent and appropriate example is given by poly(acenaphtho [1,2-b]19 which has a remarkably low band gap of approximately 0.5 eV but demonstrates very poor reversibility upon p-doping.In this work, we report the synthesis of a conjugated polymer containing the BODIPY structure as a main chain component. The material has a low band gap of approximately 0.8 eV, and the reversibility of both n-and p-doping processes in this polymer is outstanding. The synthesis of the monomer unit (3) is summarized in Scheme 1. Functionalization of the BODIPY unit with 3,4-ethylenedioxythiophene (EDOT) was chosen because of the wellknown facile electropolymerizability of the EDOT unit and its derivatives.20 A mixture of 3,5-dichloro-8-(4-nitrophenyl)-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene 1, 21 2-(trimethyltin)-3,4-ethylenedioxythiophene 2, 22 and tetrakis(triphenylphosphine)palladium(0) was reacted in anhydrous DMF over 2 h at 160°C via microwave assisted heating. The product was purified by column chromatography and recrys-

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“…12 In this context, probes reporting predictably on both polarity and viscosity are a desirable tool in the field of fluorescence molecular sensors, since they may allow for thorough physicochemical characterization of their local environment.…”

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A fluorescent molecular rotor showing vapochromism, aggregation-induced emission, and environmental sensing in living cells

et al. 2016

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Among the plethora of recently proposed molecular sensors, those belonging to the class of fluorescent molecular rotors (FMRs) have attracted much attention owing to their peculiar photophysical properties that enable an unprecedented sensitivity towards environmental microviscosity. The usual FMR synthetic design prescribes chromophores characterized by an intramolecular rotation between two well-defined excited states, a locally excited state and a twisted internal charge transfer (TICT) state, where the sensing capabilities arise from a dual competition of the corresponding radiative/non-radiative decay processes. However, we have recently demonstrated a different modus operandi of a new subclass of solvatochromic FMRs, which exploit a solvent-independent, barrier-free intramolecular rotation of the excited dye. The rotational dynamics is modulated by local viscosity and, in turn, manifested through a variable spectral signal. In order to translate the same rotational mechanism in a versatile sensor of polarity and viscosity, we designed and thoroughly characterized a novel FMR, namely 4-(triphenylamino)-phthalonitrile (TPAP). Remarkably, in addition to a high sensitivity versus solvent polarity and viscosity, TPAP is also able to form stable fluorescent nanoparticles characterized by aggregation-induced emission, via a simple sonochemical treatment. Such peculiar features are tested in different applications aiming at illustrating its capability to report on solvatochromic and vapochromic effects, as well as to provide detailed intracellular information through bioimaging studies.

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A Molecular Rotor Based on an Unhindered Boron Dipyrromethene (Bodipy) Dye

Cited by 102 publications

References 73 publications

Conformational Effects on the Dynamics of Internal Conversion in Boron Dipyrromethene Dyes in Solution

Conformational Effects on the Dynamics of Internal Conversion in Boron Dipyrromethene Dyes in Solution

New Redox Stable Low Band Gap Conjugated Polymer Based on an EDOT−BODIPY−EDOT Repeat Unit

A fluorescent molecular rotor showing vapochromism, aggregation-induced emission, and environmental sensing in living cells

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