Single-photon upconversion via hot-band absorption and assessment of the laser cooling effect of tricarbocyanine dyes

“Awakening” of the S2 Emission of Tricarbocyanine Dyes Stimulated by Interaction with Carbon Quantum Dots

“…Furthermore, a modest suppression of the S 1 absorption upon the dye immobilization onto CQD agrees well with a similar effect upon polymethine dye binding to other carbon particles, nanodiamond colloid . Second, the dependence of the spectral properties of tricarbocynine dyes on the solvent used is well-known, and the increasing S 0 → S 2 absorption band near 440 nm is consistent with a similar effect observed in high-viscosity solvents due to suppression of low-frequency molecular vibrations, as was reported by Laboe et al Suppression of the low-frequency vibrations both in the ground and excited states can be concluded, on one hand, from the reduced QY of the dye anti-Stokes photoluminescence (ASPL) assisted by the hot band absorption (HBA) (Figure d), where the low-frequency vibrations of the ground state play a major role in promoting the HBA-assisted ASPL and, on the other hand, from the narrowing S 0 → S 1 absorption band near 840 nm via reduced contribution of the high-energy vibronic tail (Figure a). Third, dilution of the composite solution leads to recovery of the initial spectral shape of the absorption of the free dye (Figure S4), which indicates there is a weak physisorption of the dye molecules on the surface of CQD.…”

“…27 Therefore, increasing solution concentration should facilitate bending of the dye backbone that bears sulfonic groups, which is evident from activation of the vibronic sideband in dye 3 at ∼775 nm in the absorption spectrum (Figure 6b), corresponding to low-energy (∼1000 cm −1 ) bending deformations of the dye chromophore. 24 The distorted geometry of these molecules leads to further suppression of the S 2 emission (Figure 6c). However, increasing solution concentration of 1 with neutral terminal groups which do not have electrostatic attraction with counterions gives no remarkable effect in both absorption and emission spectra (Figure 6b,c).…”

“…The increasing solution concentration facilitates association of the cation and anion moieties, whereas dilution leads to their decoupling . Therefore, increasing solution concentration should facilitate bending of the dye backbone that bears sulfonic groups, which is evident from activation of the vibronic sideband in dye 3 at ∼775 nm in the absorption spectrum (Figure b), corresponding to low-energy (∼1000 cm –1 ) bending deformations of the dye chromophore . The distorted geometry of these molecules leads to further suppression of the S 2 emission (Figure c).…”

Dynamics of Excitons in Conjugated Molecules and Organic Semiconductor Systems

“…For example, it was shown that activation energy in tricarbocyanine dyes is relatively low (∼55 meV), which corresponds to the low-energy skeletal CNC in-plane bending deformation of the chromophore chain, whereas HBA can proceed from a relatively high vibrational level corresponding to the CN stretch as well. 580 According to eq 30b, the relative population ratio for the CNC bending level (670 cm −1 ) is about 4%, that for the CH bending (910 cm −1 ) is 1.2%, and that for the CN stretch (1360 cm −1 ) is only 0.14%. This leads to the fact that HBA-assisted ASPL should be more effective by 1 order of magnitude when it is assisted by lowenergy bending than when it is assisted by high-energy stretching vibrations (Figure 69).…”

“…707 The only exclusion is known for tricarbocyanine dyes, which demonstrate QY up to 15% with emission wavelength above 830 nm. 580 Combination of eqs 39 and 40a leads to the conclusion that the measured lifetime of the exciton should increase with increasing band gap of the molecule. This was particularly demonstrated experimentally by Dimitrov et al by comparing 16 conjugated polymers with different band gaps 708 (Figure 85).…”