Triplet BODIPY and AzaBODIPY Derived Donor‐acceptor Dyads: Competitive Electron Transfer versus Intersystem Crossing upon Photoexcitation
Triplet BODIPY and AzaBODIPY Derived Donor‐acceptor Dyads: Competitive Electron Transfer versus Intersystem Crossing upon Photoexcitation
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DOI：
10.1002/cptc.201900189
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发表时间：
2019
期刊：
影响因子：
3.7
通讯作者：
Shuai Shao;H. Gobeze;Venugopal Bandi;C. Funk;Brian Heine;M. J. Duffy;V. Nesterov;Paul A. Karr;F. D’Souza
中科院分区：
文献类型：
--
作者：
Shuai Shao;H. Gobeze;Venugopal Bandi;C. Funk;Brian Heine;M. J. Duffy;V. Nesterov;Paul A. Karr;F. D’Souza
合成了双碘β-吡咯取代的BF_2螯合二吡咯亚甲基(I_2BODIPY)及其结构类似物BF_2螯合氮杂二吡咯亚甲基(I_2ZAA_BODIPY)，并用不同的方法表征了它们。这些增敏剂进一步用富勒烯C60在中心硼原子上官能化，以建立供体-受体共轭化合物。利用光谱、电化学和计算等方法对这些共轭化合物进行了表征，并建立了它们的能级。在I2BODIPY和I2azaBODIPY的激发下观察到了系统间交叉来填充三重态，然而，测得的I2azaBODIPY(Kisc∼1011s−1)的kISC速率比I2BODIPY(Kisc∼109s−1)高近两个数量级。尽管I2BODIPY-C60和I2azaBODIPY-C60的供体-受体距离基本相同，但HOMO和LUMO能级的能级、KISC和位置控制了二联体进行电子转移的能力。自由能计算表明，光诱导电子转移过程在热力学上是可行的，仅从两个共轭中的单重态激发态。因此，在I2BODIPY-C60dyad的情况下，观察到从1I2BODIPY*与系统间交叉竞争的电子转移，而在I2azaBODIPY-C60dyad的情况下，azaBODIPY的激发导致了涉及邻苯二酚桥的短暂电荷转移状态，随后填充了低位的3I2azaBODIPY*状态，而没有促进涉及C60的电荷分离过程。在极性和非极性溶剂中，I2BODIPY-C60共轭化合物的电荷分离态的寿命都在ns范围内。
The bis‐iodo β‐pyrrole‐substituted BF2‐chelated dipyrromethene, I2BODIPY, and its structural analogue BF2‐chelated aza dipyrromethene, I2azaBODIPY, carrying a nitrogen at themeso‐position instead of carbon, were synthesized and characterized as new set of triplet sensitizers using different techniques. These sensitizers were further functionalized with fullerene, C60, at the central boron atom to build donor‐acceptor conjugates. Using spectral, electrochemical, and computational methods, these conjugates were characterized, and the energy levels were established. Intersystem crossing to populate the triplet state was observed upon excitation of I2BODIPY and I2azaBODIPY, however, the measured rates ofkISCwere found to be nearly two orders of magnitude higher for I2azaBODIPY (kISC∼1011s−1) compared to I2BODIPY (kISC∼109s−1). The energetics,kISC, and position of HOMO and LUMO levels was found to control the ability of the dyad to undergo electron transfer, although the donor‐acceptor distances were virtually the same in both I2BODIPY‐C60and I2azaBODIPY‐C60conjugates. Free‐energy calculations revealed that the photoinduced electron transfer process was thermodynamically feasible from only the singlet excited states in both conjugates. Consequently, electron transfer from the1I2BODIPY* in competition with intersystem crossing was witnessed in the case of I2BODIPY‐C60dyad while in the case of I2azaBODIPY‐C60dyad, excitation of azaBODIPY led to a short‐lived charge transfer state involving the catechol bridge followed by populating the low‐lying3I2azaBODIPY* state without promoting the process of charge separation involving C60. The lifetime of the charge‐separated states was in the ns range in the I2BODIPY‐C60conjugate both in polar and nonpolar solvents.