Photophysics of cyanine dyes: Subnanosecond relaxation dynamics in monomers, dimers, and H- and J-aggregates in solution
Photophysics of cyanine dyes: Subnanosecond relaxation dynamics in monomers, dimers, and H- and J-aggregates in solution
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DOI：
10.1021/jp9621134
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发表时间：
1997-04-03
影响因子：
3.3
通讯作者：
Serpone, N
中科院分区：
文献类型：
--
作者：
Khairutdinov, RF;Serpone, N
用皮秒激光光解方法研究了三种花菁染料(I)1，1‘-二乙基-2，2’-花菁(PIG)，(II)3，3‘-二硫-2，2’-碳菁溴(染料1)，(III)3，3‘-二乙基二硫-2，2’-碳菁(染料2)在水和甲醇-水介质中的光物理性质。在中等浓度下，PIC在5M氯化钠/水中的溶液含有单体、II-聚集体和J-聚集体；染料1的水/甲醇溶液主要由单体和H-聚集体(二聚体和较高的n-MERS)组成；染料2的水溶液只含有单体和二聚体。H-和/或J-聚集体在PIC和染料1-花菁溶液中的光解导致相应聚集体吸收带的光漂白，随后以两相动力学的方式衰减。讨论了激发态聚集体失活的两种机制。在第一种情况下，激发的单重态的非辐射衰变导致聚集体及其周围的溶剂层的相当大的加热，使得在泵浦-探测实验中的探测激光在激发后被强烈衰减(例如，参见J.Phys。化学。1995年、99、11952)。这种加热也可以由另一种机制引起，这种加热随后导致聚集体的部分溶解(解聚)，随后在冷却时缓慢重塑。也就是说，II聚集体的单重态激发态的驰豫也可以部分地通过激子-激子湮没发生，就像在高激光泵浦强度下J聚集体中所发生的那样。在这种情况下，与J-聚集体相比，II-聚集体的激发单重态寿命更长，这可能是由于II-聚集体中激子-激子湮没过程效率较低(较慢)，这意味着与J-聚集体中普遍存在的强耦合相比，激子耦合较弱。对于染料单体，单重态激发态寿命(I)随染料分子上脂肪残基长度的增加而增加，(Ii)随染料分子的二聚化而增加。二聚作用限制了染料多亚甲基链的扭转动力学，并减少了非辐射失活通道。这项工作的一个重要结论是，在皮秒激光激发后的短时间内，聚集在聚集体中的热能，以及随后对周围溶剂壳的加热，导致溶解成较小的聚集和单体，为S-1-S-1在激发的染料聚集体的失活中提供了另一条湮灭途径。这可以为卤化银颗粒的J-聚集体敏化中净效率的降低(即电荷注入效率的降低)提供附加/替代途径(见例如Lanzafame等人)。化学。太棒了。1996、210、79)。
The photophysics of three cyanine dyes (i) 1,1'-diethyl-2,2'-cyanine iodide (pseudoisocyanine, PIG), (ii) 3,3'didodecyldithia-2,2'-carbocyanine bromide (dye 1), and (iii) 3,3'-diethyldithia-2,2'-carbocyanine iodide (dye 2) have been examined by picosecond-laser photolysis in aqueous and methanolic-aqueous media. At moderately high concentration, solutions of PIC in 5 M NaCl/water contain monomers, II-aggregates, and J-aggregates; dye 1 water/methanol solutions consist mostly of monomers and H-aggregates (dimers and higher n-mers); aqueous dye 2 solutions contain only monomers and dimers. Photolysis of H- and/or J-aggregates in PIC and dye 1 cyanine solutions leads to photobleaching of the respective aggregate absorption bands and subsequently decays by biphasic kinetics. Two mechanisms are discussed for the deactivation of excited aggregates. In the first, nonradiative decay of the excited singlet states results in considerable heating of the aggregates together with their surrounding solvent shells causing the probe laser light in a pump-probe experiment to be strongly attenuated after excitation (see, e.g., J. Phys. Chem. 1995, 99, 11952). This heating, which subsequently leads to partial dissolution of the aggregates (deaggregation), later reformed slowly on cooling, can also arise from another mechanism. That is, relaxation of singlet excited states of II-aggregates can also occur, in part, by exciton-exciton annihilation as occurs in J-aggregates at high laser pump intensities. In this case, the longer lived excited singlet states of II-aggregates, relative to those of J-aggregates, are Likely due to a less efficient (slower) exciton-exciton annihilation process in II-aggregates which would infer a weaker exciton coupling in comparison to the strong coupling known to prevail in J-aggregates. For dye monomers, singlet excited state Lifetimes increase (i) with an increase in the length of the aliphatic residues attached to the dye molecule and (ii) with dimerization of the dye molecules. Dimerization restricts torsional dynamics along the dyes polymethine chain and diminishes the nonradiative deactivation channel. An important conclusion from this work is that the thermal energy stored in the aggregates in a short time after picosecond-laser excitation, and the subsequent heating of the surrounding solvent shells, leading to dissolution to smaller aggregates and monomers, provides another pathway to S-1-S-1 annihilation in the deactivation of excited dye aggregates. This could provide an added/alternative path for the decrease of net efficiency (i.e., decrease in charge injection efficiency) in J-aggregate sensitization of silver halide grains (see, e.g., Lanzafame et al. Chem. Phys. 1996, 210, 79) in laser-imaging technologies.