Benefits of using BODIPY–porphyrin dyads for developing deep-red lighting sources

Abstract

Neutral free-base and metallo-porphyrins have been successfully used in organic light-emitting diodes (OLEDs) and solar cells. [1][2][3][4][5] This field is mainly driven by their ease of modification to enhance light-harvesting and photoluminescence (PL) properties based on an efficient energy and/or electron transfer process from moieties attached at the periphery to the porphyrin core.This feature of dyad-like porphyrins is of utmost relevance for lighting schemes, since it could open a new avenue to decouple charge transport and emission processes by only using one active compound. This is more critical in light-emitting electrochemical cells (LECs) than in OLEDs, in which the charge transport is not performed by the emitter, but by a multilayered device architecture. 6,7 In LECs, the presence of mobile ions in the active singlelayer assists the charge injection process, while the charge transport, electron-hole recombination, and emission processes occur via the emitter. 8-10 Thus, to define clear guidelines to design LEC materials that are intrinsically able to decouple charge transport and emission is a challenge in the field. 8-10As an alternative, the host-guest approach by (i) using OLED-host materials doped with ionic liquids, 11 (ii) mixtures of iTMCs, 12-14 and (iii) using ionic-based small-molecule charge transporters, 15 has been explored in LECs to date. All these approaches show the typical problem of the host-guest strategy, that is, to determine the optimum doping level and effective doping range, which are typically very low and narrow, respectively. Here, a low doping level causes an inefficient energy transfer (ET) from the host to the guest, resulting in a poor color purity and device performance, while a high concentration of the guest leads to the a strong self-quenching of its emission and a prominent phase separation in thin films. The latter are paramount in determining the overall device performance. Herein, we report on a new concept to decouple charge transport and emission in small-molecule LECs by using only one active compound mixed with an ionic electrolyte. To this end, we took advantage of our mature experience in the synthesis of BODIPYporphyrin dyads and their implementation in solar cells [16][17][18][19] to further expand their application to lighting schemes, in which the above-mentioned drawbacks of the host-guest approach are circumvented. In detail, two BODIPY-porphyrin dyads have been designed -Scheme 1. On one hand, these dyads fulfill all of the key requirements, such as (i) the energy alignment of the electronic levels between the BODIPY and the porphyrin evokes in a chargeScheme 1 Synthesis of BODIPY-porphyrin dyads 1 and 2.

Light-Emitting Electrochemical Cells: A Review on Recent Progress

“…It should, however, be acknowledged that a vast majority of the subsequent research on iTMC-LECs have employed an additional electrolyte (often an ionic liquid) in order to attain a reasonably fast turn-on time [4,5]. The LEC field has up until now been dominated by these two principal classes of compounds, although new groups of functional materials, in the form of non-ionic luminescent small molecules [6][7][8][9][10][11][12][13][14], ionic fluorescent small molecules [15][16][17], quantum dots [18,19], and perovskites [20,21], have emerged more recently. Figure 1c presents the chemical structures of a CP, an iTMC, and a luminescent small molecule, as well as a number of electrolytes that have been utilized in recent high-performance LEC devices.…”

A theoretical and experimental NMR study of BODIPY 493/503: difluoro{2‐[1‐(3,5‐dimethyl‐2H‐pyrrol‐2‐ylidene‐N)ethyl]‐3,5‐dimethyl‐1H‐pyrrolato‐N}boron

“…Compound 1 is bright, green fluorescent dye with similar excitation and emission to fluorescein with several uses in biochemistry, for staining lipids, membranes and other lipophilic compounds, because they exhibit narrow emission bandwidths, they have high extinction coefficient and fluorescence quantum yields and they are photostable. [1] Other applications of these dyes are related to fluorescent probes, [2][3][4] deep-red lighting sources, [5] bioactive CO-releasing molecules [6] and solar cells, [7] amongst many others. [8][9][10] Concerning BODIPY NMR properties, there are several compounds with reported data (Scheme 1) especially related to [11] ; 4, 1 J 11B19F = 33.4 Hz [12] ; 5, 11 B = 0.28, 1 J 11B19F = 28.7 Hz [13] ; 6, 11 B = 0.…”

Cunning metal core: efficiency/stability dilemma in metallated porphyrin based light-emitting electrochemical cells

“…7 Recently, we have demonstrated that an efficient energy transfer process from peripheral BODIPY units to the zinc porphyrin core in dyad-like compounds can be exploited to decouple charge transport and emission processes in LECs. 11 This leads to very stable deep-red emitting devices, but with a moderate efficiency. The latter might be limited by the spin statistics that indicate the formation of excitons with a 1 : 3 spin distribution of singlets and triplets upon electron-hole recombination.…”

“…Metallated porphyrins have been successfully applied to develop deep-red lighting sources based on the organic lightemitting diode (OLED) [1][2][3][4][5][6][7][8][9][10] and the light-emitting electrochemical cell (LEC) 11 concepts. One of the most important advantages of porphyrins is the mature control of their photophysical features by means of a proper molecular design, namely (i) the expansion of the π-conjugation of the pyrrole unit to red-shift the emission to the near-infra red region, 3 (ii) the use of substituents at the meso position in order to enhance the photoluminescence quantum yields (ϕ), 4 to promote self-assembling, 8,10 and/or to open up the preparation of porphyrin dyads with efficient energy/electron transfer processes, 2,6,9,[11][12][13][14] and (iii) the use of different metal cores to provide new photoluminescence (PL) mechanisms like phosphorescence 2,5,6,8 and thermally activated delayed fluorescence (TADF).…”

“…One of the most important advantages of porphyrins is the mature control of their photophysical features by means of a proper molecular design, namely (i) the expansion of the π-conjugation of the pyrrole unit to red-shift the emission to the near-infra red region, 3 (ii) the use of substituents at the meso position in order to enhance the photoluminescence quantum yields (ϕ), 4 to promote self-assembling, 8,10 and/or to open up the preparation of porphyrin dyads with efficient energy/electron transfer processes, 2,6,9,[11][12][13][14] and (iii) the use of different metal cores to provide new photoluminescence (PL) mechanisms like phosphorescence 2,5,6,8 and thermally activated delayed fluorescence (TADF). 7 Recently, we have demonstrated that an efficient energy transfer process from peripheral BODIPY units to the zinc porphyrin core in dyad-like compounds can be exploited to decouple charge transport and emission processes in LECs.…”