Abstract
The electroluminescent properties of asymmetrically twisted phenanthrimidazole derivatives comprised of fluorescent anthracene or pyrene unit namely, 1-(1-(anthracen-10-yl)naphthalen-4-yl)-2-styryl-1H-phenanthro[9,10-d]imidazole (ANSPI), 1-(1-(pyren-1-yl) naphthalene-4-yl)-2-styryl-1H-phenanthro[9,10-d]imidazole (PNSPI), 4-(2-(4-(anthracen-9-yl) styryl)-1H-phenanthro[9,10-d]imidazol-1-yl)naphthalene-1-carbonitrile (ASPINC) and 4-(2-(4-(pyren-1-yl)styryl)-1H-phenanthro[9,10-d]imidazol-1-yl)naphthalene-1-carbonitrile (PSPINC) for blue OLEDs have been analyzed. The asymmetrically twisted conformation interrupt π-conjugation effectively results in deep-blue emission. The pyrene containing PSPINC based non-doped blue device (476 nm) shows maximium efficiencies (current efficiency (ηc)-4.23 cd/A; power efficiency (ηp)-2.86 lm/W; external quantum efficiency (ηex)-3.48%: CIE (0.16, 0.17) at 3.10 V. Among the doped blue devices, An(PPI)2:ASPINC shows high efficiencies (ηc-12.13 cd/A; ηp-5.98 lm/W; ηex-6.79%; L-23986 cd m−2; EL-458 nm) at 3.15 V with CIE (0.15, 0.17) than An(PPI)2:PSPINC based device which is inconsistent with non-doped device performances. The green and red PhOLEDs show higher efficiencies with Ir(ppy)3: ASPINC (ηc-50.6 cd/A; ηp-53.4 lm/W; ηex-17.0%; L-61581 cd m−2; EL-501 nm, CIE (0.31, 0.60) at 3.32 V and (bt)2Ir(dipba): ASPINC (ηc-15.2 cd/A; ηp-16.5 lm/W; ηex-14.5%; L-13456 cd m−2; EL-610 nm), CIE (0.63, 0.36) at 3.20 V, respectively. The complete energy transfer between the host and dopant molecules improved the efficiency of PHOLEDs.
Highlights
The bulky substituent at C-9 and C-10 of anthracene derivatives show blue emission due to rupturing of π-conjugation because of non-coplanar geometry leads[10,11]
The blue emitters ANSPI, PNSPI, ASPINC and PSPINC were purified by column chromatography and characterized by 1H, 13C NMR, mass and elemental analysis
The minimum energy conformation of ANSPI, PNSPI, ASPINC and PSPINC shows that the orthogonal dihedral angle (~83.0°) between the side chain at N 23 and substituent at C 25 i.e., 10-(4-vinylphenyl)anthracene (ASPINC) and 1-(4-vinylphenyl)pyrene (PSPINC)/styryl (ANSPI, PNSPI) and side coupling of naphthyl anthracene (ANSPI)/1-naphthylpyrene (PNSPI)/naphthonitrile (ASPINC and PSPINC) at N 23 reduces the intermolecular packing
Summary
The bulky substituent at C-9 and C-10 of anthracene derivatives show blue emission due to rupturing of π-conjugation because of non-coplanar geometry leads[10,11]. We have designed asymmetrically twisted phenanthrimidazole derivatives coupled with anthracene/pyrene units such as ANSPI, PNSPI, ASPINC and PSPINC exhibit high-energy emission and as employed a high-performance host material due to good carrier-transport ability.
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