Several important photophysical properties of the cyanine dye Cy3 have been determined by laser flash photolysis. The triplet-state absorption and photoisomerization of Cy3 are distinguished by using the heavy-atom effects and oxygen-induced triplet --> triplet energy transfer. Furthermore, the triplet-state extinction coefficient and quantum yield of Cy3 are also measured via triplet-triplet energy-transfer method and comparative actinometry, respectively. It is found that the triplet --> triplet (T1-->Tn) absorptions of trans-Cy3 largely overlap the ground-state absorption of cis-Cy3. Unlike what occurred in Cy5, we have not observed the triplet-state T1-->Tn absorption of cis-Cy3 and the phosphorescence from triplet state of cis-Cy3 following a singlet excitation (S0-S1) of trans-Cy3, indicating the absence of a lowest cis-triplet state as an isomerization intermediate upon excitation in Cy3. The detailed spectra of Cy3 reported in this paper could help us interpret the complicated photophysics of cyanine dyes.

To explore the effect of intertrimer Cu...Cu interactions on the phosphorescent properties of trimeric copper(I) pyrazolates, three new complexes with identical core cluster structures and different substituents, {[3,5-(Me)(2)-4-(Ph)Pz]Cu}(3) (MPC-P), {[3,5-(Me)(2)-4-(1-Naph)Pz]Cu}(3) (MPC-N), and {[3,5-(Me)(2)-4-(9-Anthr)Pz]Cu}(3) (MPC-A), were synthesized. The intertrimer Cu...Cu distances of the three complexes were obtained from X-ray crystallographic data or molecular dynamics simulations. The phosphorescent properties of the three complexes were investigated at various pressures. At ambient pressure, the emissions of the three complexes were dramatically different from each other. For MPC-P, the main emission band was identified as phosphorescence and MPC-N gave a predominant emission of fluorescence and a weak emission of phosphorescence. When the substitutent was replaced by an anthryl group in MPC-A, no phosphorescence was observed, except for a strong fluorescence band. The phosphorescence of the trimer copper(I) pyrazolates was assigned to the excited-state dimer/polymer *[Cu(3)](n) with LMCT characteristics. Under higher external pressures, only phosphorescent intensities of MPC-P showed considerable enhancement at pressures up to 2 GPa. External pressure reduced the intertrimer Cu...Cu distances of MPC-P and enhanced the phosphorescence intensities, providing a direct evidence to support the assignment of phosphorescence.

SummaryMolecules containing polarized NH fragments that behave as anion-binding motifs are widely used as receptors for recognition and sensing purposes in aprotic solvents. We present here a new example of a receptor, 3-amino-5-(4,5,6,7-tetrahydro-1H-indol-2-yl)isoxazole-4-carboxamide (receptor 1), which contains pyrrole, amide and amino subunits. This receptor shows both changes in its UV–vis absorption and fluorescence emission spectra upon the addition of F−, resulting in highly selectivity for fluoride detection over other anions, such as Cl−, Br−, I−, HSO4 −, H2PO4 − and AcO− in CH3CN. 1H NMR titration, time-dependent density functional theory (TDDFT) calculations and other experiments confirm that the sensing process is brought about by deprotonation of the pyrrole-NH in receptor 1.