29 Femtosecond Pump-Probe Microspectroscopy …
511
dependence was in good agreement with temperature dependence. Therefore, we can
safely conclude that transient local heating in a ps time scale owing to the nonradiative
vibrational relaxation from higher vibrational level to lower ones in the S 1 state will
accelerate the triplet state formation through the TAF.
29.5 Conclusion
We described the novel femtosecond pump-probe confocal microspectroscopic
system and its application to single organic crystals having the size of nm to μm. By
using normal transmitted light as a probe light, we demonstrated the excited-state
dynamics of individual μm-sized crystals such as CT complex and rubrene [29]. On
the other hand, back-scattering light detection made it possible to observe transient
signals of single organic nanocrystals which size was smaller than the diffraction limit
of the visible light. We succeeded in the measurement of the excimer formation of
α-phase perylene single nanocrystal and found out the size-dependent excimer formation dynamics in a ps time scale [13]. We expect our microspectroscopic system can
open new photophysical processes with nanometer size and picosecond time scale
for organic solids.
Acknowledgements This work was supported by JSPS KAKENHI Grant Number JP26107011 to
T. A. in Scientific Research on Innovative Areas “Photosynergetics”, and 19K05211 to Y. I. The
authors would like to thank Mr. O. Udaka, Mr. Y. Inoue, Mr. R. Kawasaki, Mrs. M. Murakami, and
Mr. R. Kihara who helped us directly in obtaining our experimental results in this project.
References
1. Asahi T, Sugiyama T, Masuhara H (2008) Laser fabrication and spectroscopy of organic
nanoparticles. Acc Chem Res 41:1790–1798
2. Mei J, Leung NL, Kwok RT, Lam JW, Tang BZ (2015) Aggregation-induced emission: together
we shine, united we soar! Chem Rev 115:11718–11940
3. Asahi T, Suzuki M, Masuhara H (2002) Cooperative photochemical reaction in molecular
crystal induced by intense femtosecond laser excitation: photochromism of spironaphthooxazine. J Phys Chem A 106:2335–2340
4. Suzuki M, Asahi T, Masuhara H (2005) Cooperative photochemical reaction mechanism of
femtosecond laser-induced photocoloration in spirooxazine microcrystals. Chem Phys Chem
6:2396–2403
5. Doan SC, Kuzmanich G, Gard MN, Garcia-Garibay MA, Schwartz BJ (2012) Ultrafast spectroscopic observation of a quantum chain reaction: the photodecarbonylation of nanocrystalline
diphenylcyclopropenone. J Phys Chem Lett 3:81–86
6. Itoh T, Asahi T, Masuhara H (2001) Femtosecond light scattering spectroscopy of single gold
nanoparticles. Appl Phys Lett 79:1667–1669
7. Cating EEM, Pinion CW, Christesen JD, Christie CA, Grumstrup EM, Cahoon JF, Papanikolas
JM (2017) Probing intrawire, interwire, and diameter-dependent variations in silicon nanowire
surface trap density with pump-probe microscopy. Nano Lett 17:5956–5961
511
dependence was in good agreement with temperature dependence. Therefore, we can
safely conclude that transient local heating in a ps time scale owing to the nonradiative
vibrational relaxation from higher vibrational level to lower ones in the S 1 state will
accelerate the triplet state formation through the TAF.
29.5 Conclusion
We described the novel femtosecond pump-probe confocal microspectroscopic
system and its application to single organic crystals having the size of nm to μm. By
using normal transmitted light as a probe light, we demonstrated the excited-state
dynamics of individual μm-sized crystals such as CT complex and rubrene [29]. On
the other hand, back-scattering light detection made it possible to observe transient
signals of single organic nanocrystals which size was smaller than the diffraction limit
of the visible light. We succeeded in the measurement of the excimer formation of
α-phase perylene single nanocrystal and found out the size-dependent excimer formation dynamics in a ps time scale [13]. We expect our microspectroscopic system can
open new photophysical processes with nanometer size and picosecond time scale
for organic solids.
Acknowledgements This work was supported by JSPS KAKENHI Grant Number JP26107011 to
T. A. in Scientific Research on Innovative Areas “Photosynergetics”, and 19K05211 to Y. I. The
authors would like to thank Mr. O. Udaka, Mr. Y. Inoue, Mr. R. Kawasaki, Mrs. M. Murakami, and
Mr. R. Kihara who helped us directly in obtaining our experimental results in this project.
References
1. Asahi T, Sugiyama T, Masuhara H (2008) Laser fabrication and spectroscopy of organic
nanoparticles. Acc Chem Res 41:1790–1798
2. Mei J, Leung NL, Kwok RT, Lam JW, Tang BZ (2015) Aggregation-induced emission: together
we shine, united we soar! Chem Rev 115:11718–11940
3. Asahi T, Suzuki M, Masuhara H (2002) Cooperative photochemical reaction in molecular
crystal induced by intense femtosecond laser excitation: photochromism of spironaphthooxazine. J Phys Chem A 106:2335–2340
4. Suzuki M, Asahi T, Masuhara H (2005) Cooperative photochemical reaction mechanism of
femtosecond laser-induced photocoloration in spirooxazine microcrystals. Chem Phys Chem
6:2396–2403
5. Doan SC, Kuzmanich G, Gard MN, Garcia-Garibay MA, Schwartz BJ (2012) Ultrafast spectroscopic observation of a quantum chain reaction: the photodecarbonylation of nanocrystalline
diphenylcyclopropenone. J Phys Chem Lett 3:81–86
6. Itoh T, Asahi T, Masuhara H (2001) Femtosecond light scattering spectroscopy of single gold
nanoparticles. Appl Phys Lett 79:1667–1669
7. Cating EEM, Pinion CW, Christesen JD, Christie CA, Grumstrup EM, Cahoon JF, Papanikolas
JM (2017) Probing intrawire, interwire, and diameter-dependent variations in silicon nanowire
surface trap density with pump-probe microscopy. Nano Lett 17:5956–5961