Synthesis and Optical and Electroluminescent Properties of Novel Conjugated Copolymers Derived from Fluorene and Benzoselenadiazole

Abstract

A novel series of light-emitting copolymers derived from 9,9-dioctylfluorene (DOF) and 2,1,3benzoselenadiazole (BSeD) is prepared by means of palladium-catalyzed Suzuki coupling reaction. The feed ratios of DOF to BSeD were 50:50, 85:15, 92:8, and 98:2, respectively. All of the copolymers are soluble in common organic solvents and highly fluorescent in solid state. Devices from such copolymers emit orange-red light with λmax ) 570-600 nm. The maximal EL emissions of the devices slightly redshifted gradually with increasing BSeD's contents. The maximal external quantum efficiency of the polymer light-emitting devices (PLED) reaches 1.0%, which indicates that this new seleno-containing EL polymer based on fluorene and benzoselenadiazole is a promising candidate for fabricating PLEDs.

High‐Efficiency White‐Light Emission from a Single Copolymer: Fluorescent Blue, Green, and Red Chromophores on a Conjugated Polymer Backbone

“…The compounds used in this study, 2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9,9-dioctylfluorene (1), 2,7-dibromo-9,9-dioctylfluorene (2), 4,7-bis(5-bromo-2-thienyl)-2,1,3-benzothiadiazole (3), and 4,7-dibromo-2,1,3-benzothiadiazole (4), were synthesized according to the procedure described in our previous studies [17,[19][20][21][22]. benzothiadiazole (DBT) and 2,1,3-benzothiadiazole (BT) in the copolymers is too low to be detected by 1 H NMR and elemental analysis, the actual ratios of DBT and BT can be assumed to be equal to the feed ratios.…”

“…The UV absorption of the copolymer PFO-R005 (others are identical and therefore omitted here) and photoluminescence (PL) spectra of the four different copolymers in solid films are shown in Figure 1a. It can be seen that the absorption spectra of the copolymers are practically identical to those of PFO-DBT x -BT y the PFO homopolymer [17,19] because of the very low content of DBT and BT units. In the PL spectra of the copolymers (Fig.…”

“…PFO was chosen as the blue-light-emitting polymer, with BT and DBT as the greenand red-light-emitting units, respectively. [17][18][19] We have previously reported that in the copolymer PFO-DBT, a full-energy transfer in the PFO-DBT devices is observed when the DBT content is equal to or greater than 0.05 mol % relative to the fluorene unit. [18] A similar situation was observed for PFO-BT copolymers.…”

“…We note that, because of the extremely low dopant content (less than 0.05 mol %) in the polymer main chain, it is almost impossible to determine an actual composition of the copolymers. Based on comparative studies of the initial monomer feed ratio and the elemental analysis of the resulting copolymers with higher heterocycle content in our previous studies, [16,17,[19][20][21][22] it is natural to postulate that the actual composition of copolymers with a very small heterocycle content is also very close to the feed ratio. The UV absorption of the copolymer PFO-R005 (others are identical and therefore omitted here) and photoluminescence (PL) spectra of the four different copolymers in solid films are shown in Figure 1a.…”

“…PFO-R005-G010, PFO-R010-G018, and PFO-R015-G025 copolymers show three emission peaks, which cover a wide range of the visible region, and the intensities of the green-and red-emission bands increases with increasing amount of green-and red-light-emitting units in the copolymer. From our previous studies, [16][17][18][19] the three distinguishable PL peaks of the copolymers PFO-R005-G010, PFO-R010-G018, and PFO-R015-G025 can be attributed to the individual emissions originating from the three chromophores (PFO, DBT, and BT) as a result of the incomplete energy transfer from the blue-emitting unit to the green-and red-emitting units. The PL quantum efficiencies of copolymers with small BT and DBT content (< 0.05 %) measured in the integrating sphere under 325 nm excitation (He:Cd laser) increased up to 60 % (Table 1) with increasing BT and DBT content, compared to 47 % for PFO homopolymers.…”