Synthesis and characterization of photoresponsive diphenylaminofluorene chromophore adducts of [60]fullerene
作者:Prashant A. Padmawar、Taizoon Canteenwala、Sarika Verma、Loon-Seng Tan、Long Y. Chiang
DOI:10.1039/b515055h
日期:——
A class of acceptor–keto–donor structures as hindered 9,9-di(3,5,5-trimethylhexyl)-2-diphenylaminofluoreno-methano[60]fullerene C60(>DPAF-C9) and the related bisadducts C60(>DPAF-C9)2 and C60(>DPAF-C2)2 were synthesized. They are derivatives of multiphoton absorptive C60(>DPAF-C2) showing enhanced cross-sections of simultaneous two-photon absorption under laser excitation at 800 nm in nanosecond region. Molecular synthesis of these C60–DPAF conjugates involved the covalent attachment of a diphenylaminofluorene moiety to methano[60]fullerene via a keto linkage for increasing molecular acceptor–donor polarization of the chromophore in conjunction with the fullerene cage. Preparation of 7-(1,2-dihydro-1,2-methanofullerene[60]-61-carbonyl)-9,9-dialkyl-2-diphenylaminofluorene C60(>DPAF-Cn) involved cyclopropanation of C60 with a key synthon 7-α-bromoacetyl-9,9-dialkyl-2-diphenylaminofluorene. Synthesis of this synthon was achieved by a three-steps procedure starting from 2-bromofluorene via dialkylation at C9 of the fluorene ring, attachment of a diphenylamino group at C2 of dialkylfluorene, and Friedel–Craft acylation of the α-bromoacetyl group at C7 of diphenylaminofluorene. All C60–DPAF derivatives were fully characterized with the chemical structures confirmed by various spectroscopic analyses and validated by the single-crystal structural analysis data of C60(>DPAF-C2). Strong solvent-sensitive fluorescence quenching phenomena of C60(>DPAF-C2), C60(>DPAF-C9), and C60(>DPAF-C9)2 were noticed, showing no fluorescence band above 700 nm in more polar solvents, such as DMF, PhCN, and THF, while in less polar solvents (toluene, CHCl3, and CS2) a fullerenyl fluorescence band at 700–710 nm was observed. It was attributed to the occurrence of electron transfer via the singlet excited state of the fullerene moiety 1C60*(>DPAF-Cn) in the former group of the solvents. On the contrary, energy transfer processes from DPAF-Cn moiety to the fullerene cage are favored in the latter group of the solvents.
合成了一类接受体-酮-供体结构,包括受阻的9,9-二(3,5,5-三甲基己基)-2-二苯胺氟烯-美琅[60]富勒烯C60(>DPAF-C9)及相关的双加合物C60(>DPAF-C9)2和C60(>DPAF-C2)2。它们是多光子吸收C60(>DPAF-C2)的衍生物,在激光激发下800 nm的纳秒区域显示出增强的同时两光子吸收截面。这些C60-DPAF共轭物的分子合成涉及通过酮联结将二苯氨基氟烯部分共价连接到美琅[60]富勒烯上,以增加分子的接受体-供体极性,与富勒烯笼体结合。7-(1,2-二氢-1,2-美琅富勒烯[60]-61-羰基)-9,9-二烷基-2-二苯胺氟烯C60(>DPAF-Cn)的制备涉及用关键合成单元7-α-溴乙酰-9,9-二烷基-2-二苯胺氟烯对C60进行环丙烷化。该合成单元的合成通过三步法实现,起始于2-溴氟烯,通过对氟烯环的C9位的双烷基化,在双烷基氟烯的C2位上连接二苯胺基团,以及在二苯胺氟烯的C7位对α-溴乙酰基进行弗riedel-Craft酰化。所有C60-DPAF衍生物均经过全面表征,化学结构通过各种光谱分析确认,并通过C60(>DPAF-C2)的单晶结构分析数据进行验证。观察到C60(>DPAF-C2)、C60(>DPAF-C9)和C60(>DPAF-C9)2的强溶剂敏感荧光猝灭现象,在更极性溶剂(如DMF、PhCN和THF)中未观察到700 nm以上的荧光带,而在较少极性的溶剂(如甲苯、CHCl3和CS2)中观察到700-710 nm的富勒烯荧光带。这归因于在前一组溶剂中,通过富勒烯部分的单态激发态1C60*(>DPAF-Cn)发生电子转移。相反,在后者溶剂组中,DPAF-Cn部分向富勒烯笼体的能量转移过程更加有利。