A photochemical study was performed by means of femtosecond time-resolved absorption spectroscopy on novel polymorphs of thin crystalline oxotitanium(IV) phthalocyanine (OTiPc) n (n ) 2-4), β-OTiPc-L (phase I) and R-OTiPc-S (phase II), where the letters "L" and "S" mean "lying" molecular orientation and "standing" molecular orientation, respectively. A rapid change of the well time-resolved absorption spectrum in a range of 420-620 nm revealed that a part of the intrinsic exciton of β-OTiPc-L with the absorption maximum around 550 nm was in a lifetime of 0.5 ps converted to a charge-separated pair on the excitation of the 400 and 800 nm laser. The absorption bands at 430, 510, and ∼860 nm were left for a lifetime of 3 ps. The formation of the cationic π-radical inferred to be 2 (OTiPc) n-1 + is responsible for the absorption bands at 510 nm and that of the anionic species of 2 (OTi III Pc)is responsible for the band at 430 nm instead of the characteristic bands of the anionic π-radical of metallophthlocyanine around 600 nm. While the chargeseparated pair disappeared in 10 ps, another transient absorption at 490 nm was survived on the excitation of the 400 nm laser, which is assigned to the triplet exciton formed via intersystem crossing from higher state(s) of the singlet exciton. The time-correlated single photon counting technique revealed that a novel fluorescence of R-OTiPc-S with a peak at 10 420 cm -1 decaying biexponentially with a short (48-64 ps) lifetime and a long (101-416 ps) lifetime is assigned to the trapped excitons. A 10-fold increase in the initial intensity of the fluorescence at 77 K compared with at 298 K indicates that the yield of long-lived and fluorescent exciton is smaller than 0.1 on the excitation of R-OTiPc-S at 298 K.

Emission decays of triplet metal-to-ligand charge transfer states in anisotropic crystals of [Ru(1 - x)Os(x)(bpy)(3)]X(2) (bpy = 2,2'-bipyridine, X = PF(6)-, ClO(4)-, SbF(6)-, and 0.115 > x > 0.001) at approximately 300 K were measured by means of time-correlated single-photon counting. Rates of excitation hopping calculated on the basis of an interaction between transition dipoles of a donor cation and an acceptor cation are insufficient to simulate the single-exponential decays (x = 0.0099) and the multiexponential decays (x = 0.060 and 0.115) of the PF(6)- salt crystals. A limiting rate of excitation hopping to an imaginary cation at the van der Waals distance via a super-exchange interaction between d orbitals through the bpy ligands was determined to be 0.83 x 10(10) s(-1) on average by means of a step-by-step Monte Carlo simulation, assuming an distance-attenuation factor, beta, of the exchange interaction of 10 nm-1. The total rate of excitation hopping via both a dipole-dipole mechanism and a super-exchange mechanism to the neighboring sites of the cation was calculated to be 5.4 x 10(9) s(-1) for the PF(6)- crystal. Anisotropic diffusion constants estimated from the hopping rates and lengths in the PF(6)- crystal are 9.3 x 10(-6), 9.1 x 10(-6), and 1.4 x 10(-6) cm(2)s(-1) along the a axis, the b axis, and the c axis, respectively, which are compared with an isotropic diffusion constant, 1.3 x 10(-6) cm(2) s(-1), estimated from the pseudo-bimolecular rate constant of excitation transfer to [Os(bpy)(3)](2+), using an isotropic Smoluchowski equation. A multiexponential emission decay of [Ru(0.885)Os(0.115)(bpy)(3)](PF(6))(2) was also simulated to determined the limiting rate of excitation transfer to [Os(bpy)(3)](2+) at the van der Waals distance (2.6 x 10(11) s(-1)). The magnitude of beta determined is 6.5 and 11.5 nm(-1) for the ClO(4)- and the SbF(6)- salt crystals, respectively, on reference to that of beta (10 nm(-1)) for the PF(6)- salt crystal.