【摘要】 采用TD-DFT的最优Hartree-Fock(HF)交换方法,计算以1,8-萘酰亚胺为受体(A),9,9-二甲基-9,10-二氢吖啶、吩噁嗪等为给体(D)构建的12种分子内电荷转移化合物的最低激发单重态和最低激发三重态的能级差(ΔEST),并探寻降低ΔEST的方法.结果表明:D-A型分子比相应的D-苯桥-A型分子具有更低的ΔEST.增加D与A间的扭曲二面角(空间位阻)和提高D的给电子能力能够有效地降低D-A型分子的ΔEST.计算发现4-(9,9-二甲基-9,10-二氢吖啶)-N-苯基-1,8-萘酰亚胺(4b)和4-(吩噁嗪)-N-苯基-1,8-萘酰亚胺(5b)的ΔEST分别为0.01和0.02 e V,它们的起始荧光波长分别为575 nm和621 nm,垂直激发的振子强度分别是0.0002和0.0025.这两种化合物有望成为发橙红光和红光的热激活延迟荧光材料.更多还原

【Abstract】 Thermally activated delayed fluorescence(TADF) materials are promising for the next generation of organic light-emitting diodes. To realize reverse intersystem crossing(RISC) effectively for TADF molecules requires basically small energy gap(ΔEST) between the lowest singlet(S1) and triplet(T1) excited states. In this work, 1,8-naphthalimide was selected as a fixed acceptor(A) because of its large rigid conjugate structure with a high radiative decay rate. Twelve naphthalimide-based intramolecular charge transfer(ICT) compounds were constructed by the conjunction of naphthalimide moiety with each of donors(D) including 9,9-dimethyl-9,10-dihydroacridine, phenoxazine, etc. Their energy gaps were calculated with the Gaussian 09 package at TD-DFT level using the optimal Hartree-Fock exchange method reported by Huang Shuping recently. The results show that D-A structure of naphthalimide-based ICT compounds has smaller ΔEST and longer starting fluorescence emission wavelengths(λ) than those for corresponding D-phenyl-A type. However, strong electron donor like 9-(9H-carbazol-3-yl)-9H-carbazole(DCZ) seems to have no significant effect on ΔEST and λ at high CT amount. To achieve small ΔEST of these naphthalimide-based ICT compounds, increasing the twisting angle between D and A, together with enhancing electron donating ability of D is found to be a practical strategy to stabilize the energy of the lowest locally-excited triplet state(3LE) and substantially lower the energy of its lowest CT triplet excited state(3CT). As a result, 4-(9,9-dimethyl-9,10-dihydroacridine)-N-phenyl-1,8-naphthalimide(4b) and 4-(phenoxazine)-N-phenyl-1,8-naphthalimide(5b) show small ΔEST of 0.01 e V and 0.02 e V, respectively. Their λ and oscillator strengths of vertical absorption from ground state(S0) to S1 are 575 nm and 0.0002 for 4b, while 621 nm and 0.0025 for 5b, respectively. In addition, the λ of compound 5b obtained from its photoluminescence curve is 600 nm, which consists with the computed one with an error of 0.07 e V. Therefore, compounds 4b and 5b can be expected to be potential reddish-orange and red TADF emitters.更多还原